chapter 03 periodicity

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CHAPTER 3

70

c o r e

Te reaonsp beween eecronc srucure and

cemca properes o e eemens s one o e key

conceps n cemsry. hs es a e ear o e periodic

table wc s a mos vauabe arrangemen o e eemens

o wc cemca properes can be reaed. he usua

orm o e perodc abe s a sown dagrammacay

n Fgure 301, bu n many paces n s caper (e.g. Fgure

302) e “sor orm” o e perodc abe, n wc e

ranson meas are omed (aso sown n Fgure 301),s used or cary.

In e perodc abe, e eemens are arranged n order

o ncreasng aomc number, readng rom et o rg,

op o boom (as n readng Engs). hs means a

knowng e aomc number, e poson o an eemen

can be ound by counng down e squares n s way. Try

, usng e perodc abe n Fgure 302, or posporus

(Z=15).

A group s a verca coumn conssng o eemens w e

same number o eecrons n e ouer energy eve, wc

gves ese eemens smar cemca properes. heseare numbered above e coumn and orgnay ey were

numbered rom 0 o 7, bu receny e sysem as been

canged o 0 o 17 o ncude e d–bock eemens. hs

s ess ambguous, oug bo are sown. I s en ound

a gong across a orzona row (known as a perod)

e cemca properes graduay cange rom ose o

reacve meas o ose o reacve non–meas, w e

nobe gases n e na group a e ar rg. Consder s

or e rs weny eemens sown n Fgure 302.

Vaence eecrons are eecrons n e ouermos energy

eve (e ges energy eve) o an aom. hese are

usuay e eecrons a ake par n a cemca reaconand deermne e pysca and cemca properes o e

eemen. I s ereore no surprsng a e poson

o an eemen n e perodc abe s cosey reaed o

s eecronc srucure, so s can be used as a memory

ad. A perod s a seres o eemens arranged accordng

o ncreasng aomc number, wc begns w e rs

eemen avng one eecron n a new man energy eve,

n wc e same eecron energy eve (or se) s beng

ed. Perod 1 s e n = 1 eve, perod 2 e n = 2 eve

ec. Hence e perod an eemen s n gves e number

3.1thePeriodic

table

3.1.1 Describe the arrangement of elements in

the periodic table in order of increasing

atomic number.

3.1.2 Distinguish between the terms group and

period.

3.1.3 Apply the relationship between the

electron configuration of elements and

their position in the periodic table up to

Z = 20.

3.1.4 Apply the relationship between the

number of electrons in the highest

occupied energy level for an element andits position in the periodic table.

© IBO 2007

Figure 302 The first twenty elements in the periodic

table and their electronic structures

Group

Period

1 2 3/13 4/14 5/15 6/16 7/17 0

1 1

H1

2

He2

2 3

L i2,1

4

Be2,2

5

B2,3

6

C2,4

7

N2,5

8

O2,6

9

F2,7

10

Ne2,8

3 11

Na2,8,1

12

Mg2,8,2

13

Al2,8,3

14

Si2,8,4

15

P2,8,5

16

S2,8,6

17

Cl2,8,7

18

Ar2,8,8

4 19

K2,8,8,1

20

Ca2,8,8,2

G r o u p s 1 &

2

Transition metals

Groups3/13 to 0

G r o u p s 1 &

2

Groups3/13 to 0

Usual (long) formof the periodic table Short formof the periodic table

Figure 301 Forms of the periodic table

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Periodicity

71

The predictive power of Mendeleev’s periodic table

can be seen as an example of a “scientist” as a “risk

taker”. ©IBO 2007

There is no doubt at all that when he proposed his

periodic table Mendeleev put his neck on the line. Not

only did he predict that there were some elements still

to be found, he also made many detailed predictions

about their properties, for example his predictions

with regard to Germanium (which Mendeleev referred

to as eka-silicon) are given below, along with the

properties it was found to have after its discovery in

1886, about 15 years after it had been predicted by

Mendeleev.

Whether being a risk-taker is a good thing or not isalso worth some thought, and probably evolution,

through survival of the fittest, is the final arbiter.

Having a long tail is obviously a risk for a male

peacock when trying to escape from a fox, so do the

extra peahens he attracts compensate for this risk?

Will he survive long enough to mate with them? In

scientific terms it could be argued there is now less

risk attached to proposing a new theory than there

once was as a result of Karl Popper, a 20th Century

Austrian philosopher. Popper said “Our belief in

any particular natural law cannot have a safer basis

than our unsuccessful critical attempts to refute it.”,

in other words science progresses by people trying

to disprove existing theories. About a century ago

it would have been a major disgrace in the scientific

world to have had a theory disproved, but now it

would be seen as valuable because it stimulated the

work that eventually disproved the theory which led

(hopefully) to the proposal of a better theory. Now a

real risk-taker would set out to disprove the theory of

gravity by bungee jumping without the cord!

Propery Mendeeev’s

predcon

Acua

propery

Reave

aomc mass

72.0 72.6

Densy 5.5 g cm-3 5.35 g cm-3

Appearance Lg grey sod Dark grey sod

Reacon w

ar

W reac o

orm a doxde

Reacs o orm

GeO2

Reacon w

waer

Reacs ony

w dicuy

Reacs ony

red o

Reacon w

acds

Sg reacon Does no reac

w common

acds

Reacon w

akas

No reacon Does no reac

w common

akas

Properes o

s oxde

Hg meng

pon; densy

4.7 g cm–3;ew acd base

reacons

Mes a

1115 oC;

densy 4.23g cm–3; very

weak base

Properes o

s corde

W orm

a qud

eracorde

wc bos a

under 100 oC

GeC4

s a

qud a room

emperaure

and bos a

84 oC

o energy eves a conan eecrons. On e oer and,

e group number (or e group number mnus 10 n e

modern numberng o groups 13 o 17) gves e number

o eecrons n e vaence se. hs s aso sown n

Fgure 302. Posporus, or exampe s n e rd perod,

so as eecrons n e rs ree energy eves, and n e

t group, so as ve eecrons (or 5-10) n e vaence

eve. Is eecronc srucure s ereore 2,8,5.

he rs eemen n eac perod (suc as sodum, Na)

ereore as ony one eecron n s ouer se. he

eemens n s rs group are known as e aka meas.

he as bu one eemen n eac perod (suc as corne,

C) requres one more eecron o compee s ouer se.

he eemens n s as bu one group are known as e

aogens. he na eemen n eac perod (suc as argon,

Ar) as a s eecron ses ed. hese eemens ave

e cemca reacvy and are known as e nobe gases.

Perodcy s e reguar repeang o properes accordng

o e arrangemen o eemens n e perodc abe (ey

occur a reguar nervas). I s ound a cemca andpysca properes o eemens sow perodcy e

eemens are arranged n order o ncreasng aomc

numbers and ese are dscussed n secons 3.2 and 3.3

respecvey.

TOK Risk-taking and science

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CHAPTER 3

72

c o r e

Gong down a group o e perodc abe, or successve

eemens ere are more energy eves ed w eecrons,

so e ouer eecrons are n ger energy eves and

arer rom e nuceus. he exra carge on e nuceus

s approxmaey canceed ou by addona ed ses

o eecrons, so e carge acng on e vaence eecrons

(e Efective Nuclear Charge) s approxmaey esame or eac eemen. As a resu e vaence eecrons

are urer rom e nuceus and e radus o e aoms

and e ons ormed rom ese aoms, bo ncrease. he

eecrons are aso ess srongy aaced by e nuceus

so a e ionisation energy (e mnmum amoun o

energy requred o remove an eecron rom one moe o

gaseous aoms,) and e electronegativity (a measure o

ow srongy e aom aracs e eecrons n a covaen

bond) bo decrease gong down e group. hese rends

are usraed n Fgure 303 usng as exampes, or aomc

and onc radus, e aka meas (Group 1), or onsaon

energy e nobe gases (Group 0) and e aogens (Group

7/17) or eecronegavy.

Gong across a perod o e perodc abe, e number

o proons n e nuceus and ence e carge on e

nuceus ncreases. hs means a gong across e

perod e eecrons, wc are a n e same energy

eve, are more srongy araced and ence move coser

o e nuceus causng e aomc and onc rad (or

soeecronc ons, .e. ose w e same eecronc

srucure) o bo decrease. he onzaon energy and e

3.2Physical

ProPerties

3.2.1 Define the terms first ionization energy

and electronegativity.

3.2.2 Describe and explain the trends in atomic

radii, ionic radii, first ionization energies,

electronegativities and melting points

for the alkali metals (Li→ Cs) and the

halogens (F→ I).

3.2.3 Describe and explain the trends in atomic

radii, ionic radii, first ionization energies

and electronegativities for elements

across period 3.

3.2.4 Compare the relative electronegativityvalues of two or more elements based on

their positions in the periodic table.

© IBO 2007

1. In e perodc abe, readng rom et o rg and

op o boom, e eemens are arranged n order o

A e number o proons n er nuceus.

B e number o neurons n er nuceus.

C ncreasng reave aomc mass.

D ncreasng mass number.

2. An eemen as 13 eecrons orbng e nuceus. In

wc group o e perodc abe w be ound?

A Group 1

B Group 2

C Group 3D Group 4

3. Fnd e eemen corne n e perodc abe.

a) How many eecrons w ave n s ouer

se?

b) How many uy ed eecron ses does

ave?

c) Gve e symbo o anoer eemen n e

same perod as corne.

d) Gve e symbo o anoer eemen n e

same group as corne.

e) Wa name s gven o e eemens n sgroup?

Exercise 3.1

070821 Chem Chap 3.indd 72 6/12/2007 10:51:4



Periodicity

73

Figure 303 a, b, c Some trends in various atomic

properties on going down different groups of the

periodic table

Figure 304 a,b,c Variations in some atomic properties

on going across the third period of the periodic table

(a) Variation in atomic radius across the third period

Na Mg Al Si P S Cl0

50

100

150

200

A t o m i c r a d i u s / p m

(b) Variation in ionization energy across the third period

Na Mg Al Si P S Cl I o n i z a t i o n

e n e r g y k J m o l – 1

400

600

800

1000

1200

(c) Variation in electronegativity across the third period

Na Mg Al Si P S Cl

E l e c

t r o n e g a t i v i t y

0

1

2

3

4

A t o m i c r a d i u s / p m

0

100

200

300

Li Na K Rb Cs

(a) The trend in atomic radius going down Group 1

atomic radius

He Ne Ar Kr Xe

0

5001000

1500

2000

2500

I o n i z a t i o n

e n e r g y k J m o l –

1

(b) The trend in ionization energy going down Group 0

(c) The trend in electronegativity going down Group 17

F Cl Br I At

0

1

2

3

4

E l e c t r

o n e g a t i v i t y

FDecreasing atomic & ionic radiusIncreasing electronegativityand ionization energy

Decreasing atomic & ionic radiusIncreasing electronegativity andionization energy

I

Li

Figure 305 Periodic trends

in some atomic properties

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CHAPTER 3

74

c o r e

A e et o e perod e eemens (L, Na, K) are meac

and gong across e perod e sreng o e meac

bondng ncreases as ere s an ncrease n nucear carge.

As a resu bo e number o mobe vaence eecrons

ncreases and e aomc radus decreases, gvng rse o

an ncrease n e meng pons (as e mea caons are

ed coser and more gy). A e cenre o eac perod

(C, S) gan covaeny bonded srucures occur n wcevery aom s joned o a e oers by very srong covaen

bonds, ence ave very g meng pons. Foowng s

e meng pons suddeny drop (N, P) as e eemens

ere ave non-poar, smpe moecuar srucures and ony

weak van der Waals’ orces exs beween e moecues.

Meng pons are ow, and depend on mass and sze o e

moecues P4, S

8, and C

2. hs s urer empassed w

e nobe gases (He, Ne, Ar), wc exs as snge aoms

w very weak van der Waas’ orces and ence very ow

meng pons. I mus be remembered a e meng

pon s ony a measure o e dference n e sreng o

e orces beween parces beween e sod and qud

sae, raer an a measure o e absoue magnude o suc orces, as bong pon represens.

eecronegavy bo ncrease overa gong across e

perod as e aracon o e nuceus or e eecrons

ncreases, aoug e cange n onzaon energy s

by no means smoo. hese rends are usraed or e

cemcay reacve eemens o perod 3 (Na → C) on e

graps n Fgure 304. Noe a ese varaons are muc

greaer an ose ound wn a group.

he overa rends n aomc radus, onzaon energy and

eecronegavy are summarsed n Fgure 305.

he sze o an aom aways decreases wen s convered

no a posve on (caon). hs may be because e woe

o an ouer se o eecrons as been os (e.g. wen Cs

urns no Cs+, see o Fgure 306) or because e oss o e

eecron resus n ess eecron–eecron repuson beween

e vaence eecrons (e.g. wen Mg urns no Mg+, n

wc 12 proons are now pung on ony 11 eecrons).

Conversey e sze o an aom aways ncreases wen s convered no a negave on (anon), because e

addona eecron resus n an ncrease n repuson

beween e vaence eecrons (e.g. wen F urns no F–,

n wc 10 eecrons repe eac oer more an e 9

eecrons n e F aom, see Fgure 306).

Amos every common caon (.e. posve on) s smaer

an any anon (.e. negave on), e converse ony beng

rue or e exremes suc as Cs+ and F-, usraed n

e scae drawngs sown n Fgure 306. H- s aso que

sma.

Pysca properes, suc as meng pon, bong ponand densy aso depend on e naure o e bondng

beween e parces o e eemen. hs s dea w n

muc greaer dea n Caper 4, wc soud be read n

conjuncon w s secon. Cear perodcy paerns

are vsbe n a grap o e meng pons o e eemens

agans aomc number, sown n Fgure 307.

Figure 307 The melting points of the first twenty elements

0

1000

2000

3000

4000

H He B C N O F NeLi Be Na Mg Al Si P S Cl Ar K Ca

M e l t i n g p

o i n t ( K )

Figure 306 Atom and ion sizes

CsCs

+

FF

–

070821 Chem Chap 3.indd 74 6/12/2007 10:51:4



Periodicity

75

1. Wc one o e oowng as e owes

eecronegavy?

A Boron

B Beryum

C Magnesum

D Carbon

2. Wc one o e oowng as e smaes radus?

A K

B K+

C Ca

D Ca2+

3. he crces beow represen e reave szes o e

F–, Na+, Mg2+, K+ and ons, bu no necessary n a

order. Wc one o e oowng woud gve em

n s order?

A II, I, III, IVB III, I, II, IV

C I, II, III, IV

D III, II, I, IV

Exercise 3.2

4. Gong across a gven sor perod, n wc group are

you mos key o nd e eemen w e ges

meng pon?

A Group 0

B Group 2

C Group 4

D Group 6

5. Arrange e oowng n order o ncreasng aomc

radus

Mg Cs Ca A Ba

6. For eac o e oowng properes, sae ow you

woud expec o cange n e drecon ndcaed

and gve reasons or e cange based on conceps

suc as nucear carge, sedng, eecron–eecron

repuson and aomc/onc radus.

a) he eecronegavy gong down a group.b) he aomc radus gong across a perod.

c) he radus o an anon compared o s paren

aom.

d) he rs onzaon energy gong down a

group.

e) he radus o a seres o soeecronc speces

(.e. speces avng e same eecronc

srucure, suc as C–, Ar, Na+) w

ncreasng aomc number.

Eemen Na Mg Al Si

Group 1 2 13 14

e– arrangemen1s2 2s2 2p6 3s1

2.8.1

1s2 2s2 2p6 3s2

2.8.2

1s2 2s2 2p6 3s2 3p1

2.8.3

1s2 2s2 2p6 3s2 3p2

2.8.4

# Vaence e– 1 2 3 4

1s I.E. (n eV) 5.1 7.6 6.0 8.1

2nd IE 47.3 15.0 18.8 16.3

3rd IE 71.7 80.1 28.4 33.5

4 IE 98.9 109.3 120.0 45.1

5 IE 139 141 154 167

Figure 308 IE data for some elements

I II III IV

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CHAPTER 3

76

c o r e

thealkaliMetals

he alkali metals L, Na, K, Rb and Cs (Fr as no been

ncuded because o s scarcy and nucear nsaby)

are sot maeabe meas w ow meng pons and ow

denses. he ow densy s a resu o e aoms o e

aka meas beng e arges aoms n er perod o e

perodc abe, and e sotness and ow meng ponsresu rom e ac a eac aom can ony conrbue

one eecron o e meac bondng, so s s ess srong

an or many oer meas. he meas become soter and

e meng pon decreases (reer o Fgure 310) gong

down e group as e aracon beween e nuceus and

e ouer eecrons becomes ess, as a resu o e ncrease

n e sze o e aoms.

Aka meas are cemcay very reacve and arns

rapdy on exposure o ar. he meas a ave jus one

eecron n er vaence eecron se. hs eecron s very

easy os and s s e major reason wy ey are very

reacve meas. hey aways orm ons w a snge posvecarge n er compounds. hey combne drecy w

reacve non–meas suc as oxygen, corne, bromne

and odne o orm oncay bonded compounds:

4L (s) + O2

(g) 2L2O (s) (2 × L+ and O2–)

(Na and K orm more compex oxdes)

2Na (s) + C2 (g) 2NaC (s) (Na+ and C–)

2K (s) + Br2 () 2KBr (s) (K+ and Br–)

2Cs (s) + I2 (s) 2CsI (s) (Cs+ and I–)

Gong down e group, as e aomc radus ncreases, e

onzaon energy o e eemens decreases, e reacvy

o e eemens ncreases. hs s bes usraed by e

reacon o e eemens w waer. A o e meas

reac w waer o orm a souon o e mea ydroxde

and ydrogen gas, accordng o e equaon beow (M

represens e aka mea):

2M(s)+ 2H2O () 2M+ (aq) + 2OH– (aq) + H2 (g)

or exampe n e case o sodum:

2Na (s) + 2H2O () 2Na+ (aq) + 2OH– (aq) + H

2 (g)

W um, e reacon occurs sowy and seady. In

e case o sodum e reacon s vgorous, producng

enoug ea o me e sodum wc zzes around on

e surace que vgorousy. W poassum e reacon

s voen and e ea produced s enoug o gne e

ydrogen evoved, wc burns w a purpe lame. In a

cases e souon becomes srongy akane owng o eormaon o ydroxde ons.

3.3cheMical

ProPerties

3.3.1 Discuss the similarities and differences in

the chemical properties of elements in

the same group.

© IBO 2001

Figure 310 Properties of the alkali metals

Alkali Metals 3L

11Na

19K

37Rb

55Cs

Electronic Structure 2,1 2,8,1 2,8,8,1 2,8,8,18,1 2,8,8,18,18,1

Melting Point – K 454 371 336 312 302

Increasingatomic and ionic radius

Decreasing

ionization energy

Decreasing

electronegativity

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Periodicity

77

thehalogens

he halogens F, C, Br and I (A as no been ncuded

because o s scarcy and nucear nsaby) are very

reacve non–meas a occur n e penumae group o

e perodc abe, ence ey a requre jus one eecron

o compee er vaence se.

A o e eemens exs as daomc moecues (F2, C

2, Br

2,

I2) n wc e aoms are joned by snge covaen bonds.

Gong down e group er sae, a room emperaure

and pressure, canges as e sreng o e van der

Waas’ orces beween e moecues ncreases w moar

mass. Fuorne and corne are gases, bromne a qud

and odne a sod a orms a purpe vapour on eang.

he aogens are are a que eecronegave eemens.

hey requre jus one eecron o compee er vaence

se, ence ey ready gan eecrons o orm e sngy

carged ade ons (F

–

, C

–

, Br

–

, I

–

). he ease w wcey gan eecrons decreases gong down e group, as e

eecrons ganed are urer rom e nuceus and ence

ess srongy araced. hs means a, n conras o e

aka meas, e reacvy o e aogens decreases gong

down e group.

he aogens are ony sgy soube n waer as ey

are non–poar and ence can ony bond by weak van der

Waas’ orces o e poar waer moecues. Concenraed

souons o corne ave a green nge and ose o

bromne darken rom yeow roug orange o brown as

e concenraon ncreases. In non–poar sovens, suc

as exane, odne orms e voe souon a woud beexpeced, bu n poar sovens, suc as waer and eano,

e souon s a brown coour. In aqueous souon e

aogens dssocae sgy o orm an acdc souon:

X2 (aq) + H

2O () H+

(aq) + X– (aq) + HOX (aq) (were X s e aogen and HOX s a weak acd)

For exampe w corne:

C2 (aq) + H

2O () H+ (aq) + C– (aq) + HOC (aq)

he compound HOX can ready donae s oxygen o oer

subsances, so acs as an oxdan. Corc(I) acd (HOC)

w, or exampe, oxdse cooured dyes o coouress

producs. he second sage o e es or corne, n

wc urns mos bue mus paper rom bue o red

(e acdc souon) and en beaces o coouress,

depends on s reacon. As a resu corc(I)acd, and

s conjugae base e corae(I) on (OC–) are used as

beaces (e.g. or paper). hey are aso oxc o mcrobes,

ence ey are used as dsnecans and corne s usedn waer reamen.

he aogens combne w meas o gve oncay bonded

sas conanng e ade on. hese sas are usuay

we and soube n waer gvng coouress souons.

he common nsoube ades are ose o ead and

sver (oug e ead(II) sas are moderaey soube n

bong waer). hese nsoube sas can be precpaed by

addng souons conanng e ade on o a soube sa

conanng e mea on. Lead(II) odde (PbI2) s easy

recognsed because o s brg yeow coour and s

s a convenen es or e odde on. he usua es or

ade ons s owever o add due nrc acd (o prevencarbonaes ec. gvng a precpae) oowed by aqueous

sver nrae o a souon o e unknown subsance. he

Halogens 9F

17C

35Br

53I

Electronic Structure 2,7 2,8,7 2,8,8,7 2,8,8,18,7

Colour Pae yeow Yeow green Red brown Back/dark purpe

State at room T & P Gas Gas Lqud Sod

Increasing

atomic and ionic radius

Decreasing

ionization energy

Decreasing

electronegativity

Figure 311 Properties of the halogens

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CHAPTER 3

78

c o r e

ormaon o a precpae (see equaon beow) ndcaes

a a corde, bromde or odde on s presen (noe

a because AgF s soube, e luorde does no gve a

precpae). Sver corde (AgC) s we, bu rapdy

darkens roug purpe o back n sung roug

poodssocaon o sver and corne. Sver bromde

(AgBr) s an of–we (or cream) coour and sver odde

(AgI) a pae yeow.

Ag+(aq) + C–(aq) AgC(s);

we precpae, a darkens n g

Ag+(aq) + Br–

(aq) AgBr(s);cream precpae

Ag+(aq) + I–

(aq) AgI(s);pae yeow precpae

Bo e eecronegavy and oxdsng power o e

aogens decrease gong down e group as e sze o eaoms ncreases and e aracon beween e nuceus

and e eecrons becomes ess. As a resu, gong down

e group, e eemens become ess poweru oxdsng

agens. hs means a a ger aogen w dspace a

ower aogen rom s sas, or exampe, corne w

oxdse odde ons o odne and s may be deeced by

e souon cangng coour rom coouress o brown. A

ower aogen canno owever dspace a ger aogen

rom s sas, e.g. odne w no oxdse corde ons o

corne:

C2(aq) + 2 I–

(aq) I2(aq) + 2 C–

(aq)

I2(aq) + 2 C–

(aq) C2(aq) + 2 I–

(aq)

he resus o dspacemen reacons o s ype, and

precpaon reacons w aqueous sver ons, are

summarsed n Fgure 313.

Hade on

Reagen F– Cl– Br– I–

Aqueous Ag + No reacon

We precpae(urns back n

sung)

Ag++C– AgC

Cream precpae

Ag++Br– AgBr

Pae yeow precpae

Ag++I– AgI

Chlorine No reacon No reaconSouon urns yeow

en brown

C2+2Br– Br

2+2C–

Souon goes yeow

en back precpae

C2+2I– I

2+2C–

Bromine No reacon No reacon No reacon

Souon goes yeow

en back precpae

Br2+2I– I

2+2Br–

Iodine No reacon No reacon No reacon No reacon

Figure 313 Summary of some reactions of the halide ions

070821 Chem Chap 3.indd 78 6/12/2007 10:51:4



Periodicity

79

Gong across a perod o e perodc abe, e naure o

e eemens canges, as sown n Fgure 315. A e et

and sde e eemens (e.g. Na & Mg) ave reavey ow

onzaon energes and so ey bond o oer eemens oorm onc compounds n wc ey ave os er vaence

eecrons and exs as caons. hs s ypca meac

beavour. he oxdes o ese eemens are ereore onc

and conan e oxde on. he oxde on can orm a bond

o ydrogen ons and as a resu ese onc oxdes ac as

bases dssovng n waer o gve akane souons and

neurasng acds o produce a sa and waer:

trendsintheoXidesofthe

Period3eleMents

3.3.2 Discuss the changes in nature, from ionicto covalent and from basic to acidic, of

the oxides across period 3.

© IBO 2001 O2– (s) + H2O () 2OH–(aq)

O2– (s) + 2H+ (aq) H2O ()

W sodum oxde:

Na2O (s) + H

2O () 2Na+ (aq) + 2OH– (aq)

W magnesum oxde:and ydrocorc acd

MgO (s) + 2HC (aq) Mg2+ (aq) + 2C– (aq)

Aumnum oxde s ampoerc (a s, w reac w

and ence dssove n, bo acds and akas):

A2O

3 (s) + 6H+ (aq) 2A3+ (aq) + 3H

2O ()

A2O

3 (s) + 2OH– (aq) + 3H

2O () 2A(OH)4– (aq)

Perod 3 eemens Na Mg A S P S C Ar

Eecronc srucure 2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

Bong pon / K 1156 1380 2740 2528 553 718 238 87

Meac / non-meac Meac MeaodNon-

meac

Iner

gas

Decreasingatomic radius

Increasingionisation energy

Increasingelectronegativity

Decreasing

metallic character

Increasinghydrolysis of chlorides

Increasingacidic oxides

Figure 314 Trends across period 3

070821 Chem Chap 3.indd 79 6/12/2007 10:51:



CHAPTER 3

80

c o r e

I ereore dspays e properes o bo meac and

non–meac oxdes. Reer o Fgure 315.

Movng owards e mdde o e perodc abe e

onzaon energy becomes oo grea or caon ormaonand e eemens end owards non–meac beavour. In

s regon e eemens (e.g. C and S) bond by means

o covaen bonds. Carbon doxde reacs reversby w

waer o orm a weaky acdc souon

CO2

(g) + H2O

() H+

(aq) + HCO3–(aq)

Scon doxde as e acd–base acvy, bu does

sow weaky acdc properes by sowy dssovng n o

concenraed akas o orm scaes.

SO2

(s) + 2OH–(aq) SO

32–

(aq) + H2O ()

A e ar rg o e perod e eemens (excep or e

nobe gases) connue o be abe o orm covaen bonds

by sarng eecrons w oer non-meas, bu ganng

an addona eecron aso becomes energecay easbe.

hs means a ese eemens (e.g. S and C) aso ave e

opon o combnng w meas o orm onc compounds

n wc ey exs as anons (e.g. S2– and C–).

he oxdes o ese eemens reac compeey wen

dssoved n waer o orm acdc souons. For exampe

posporus(V) oxde reacs o orm a souon o

posporc(V) acd a weak acd and suur roxde reacs

o orm a souon o suurc acd, a srong acd:

P4O10(s) + 6H2O

() 4H+(aq) + 4H2PO4–

(aq)

SO3

(s) + H2O

() H+

(aq) + HSO4–(aq)

hese rends n e properes o e compounds o e

eemens on gong across e rd perod are dscussed n

consderaby more dea n e nex secon.

1. he reacvy o e aka meas ncreases n e

order

A Na, K, L

B K, Na, L

C L, Na, K

D L, K, Na

2. An aqueous souon o corne acs as a beac. hs

s because e souon

A acs as an oxdan and convers e

cooured dye o a coouress produc.B acs as a base and convers e cooured

dye o a coouress produc.

C acs as a reducan and convers e

cooured dye o a coouress produc.

D acs as an acd and convers e

cooured dye o a coouress produc.

3. Gong down e aogen group e sae o e

eemens, a room emperaure and pressure, canges

rom gas o qud o sod. he reason or s s a

A e sreng o e bonds beween e

aoms ncreases.B e sreng o e orces beween e

moecues ncreases.

C e poary o e moecues ncreases.

D e eecronegavy o e aoms

decreases.

Formua Na2O MgO A

2O

3SO

2P

2O

5SO

3C

2O

7

Rao o

Aoms2 : 1 2 : 2 2 : 3 2 : 4 2 : 5 2 : 6 2 : 7

Bondng Ionc IoncHgy poar

covaen

Poar

covaenPoar covaen

Poar

covaenPoar covaen

Acd-baseCaracer

Basc Basc Ampoerc Weaky acdc

Acdc Acdc Acdc

Oer Oxdes Na2O

2P

2O

3SO

2CO

2& C

2O

Figure 315 Some properties of the period 3 oxides

Exercise 3.3

070821 Chem Chap 3.indd 80 6/12/2007 10:51:



Periodicity

81

a) I s s e case, wre a baanced onc

equaon or e ormaon o e precpae.

A coeague suggess a s woud aso be e

expeced resu e souon ad conaned a

mxure o corde and odde ons.

b) How coud e expermener es scoeague’s ypoess? Descrbe wa s/e

soud do, and gve e resus you woud

expec or bo e bromde on and e

mxure o corde and odde ons. Wre

baanced equaons or any reacons a you

descrbe.

9. For eac o e oowng pars, sae weer a

reacon woud or woud no occur on mxng,

expanng your reasonng. In cases were a reacon

does occur, wre an onc equaon or e reacon

and sae any coour cange you woud expec osee.

a) corne and aqueous sodum bromde.

b) bromne and aqueous poassum luorde.

c) bromne and aqueous cacum odde.

d) odne and aqueous magnesum bromde.

10. Properes o e eemens and er compounds

oten sow reguar varaons w respec o er

poson n e perodc abe.

a) Descrbe e genera rend n acd–base

caracer o e oxdes o e eemens n erd perod (Na o Ar). Gve one exampe

eac o an acdc oxde and a basc oxde and

sow w equaons ow ese oxdes reac

w waer.

b) How does e oxdsng sreng o e

aogens vary down e group? Accoun or

s rend.

c) How does e reducng sreng (.e. e

aby o donae eecrons) o e aka

meas vary down e group? Accoun or s

rend.

4. On gong across a perod o e perodc abe, e

eemens end o become ess meac n caracer.

Wc one o e oowng s no an ndcaon o

s rend?

A here s an overa ncrease n moar

mass.

B here s an ncrease n eecronegavy.C here s an overa ncrease n onzaon

energy.

D here s a cange n bond ype rom

onc o covaen.

5. Wc one o e oowng s no rue o e aka

meas?

A hey ave a g densy.

B hey orm onc compounds.

C her cordes dssove n waer o orm

neura souons.D her oxdes dssove n waer o orm

akane souons.

6. a) Wre a baanced equaon or e reacon o

sodum w waer.

b) Wa woud be seen as s reacon

occurred?

c) To wa cass o cemca reacons does s

beong?

d) Descrbe ow e cange n e caracer

o s reacon can be used o compare e

reacvy o sodum w ose o um

and poassum.

7. Gve e coours o e oowng:

a) Iodne vapour.

b) he precpae nay ormed wen

aqueous barum corde reacs w aqueous

sver nrae.

c) he coour s canges o wen exposed o

sung or a ong me.

d) he coour o e souon wen corne s

bubbed roug aqueous sodum bromde.

e) he precpae ormed by e reacon o

aqueous souons o ead(II) nrae andpoassum odde.

8. Wen aqueous sver nrae s added o a coouress

aqueous bromde souon, n e presence o excess

nrc acd, an of–we precpae orms. he

expermener assumes a s sows e presence

o bromde ons n e souon.

070821 Chem Chap 3.indd 81 6/12/2007 10:51:



CHAPTER 3

82

a h l

he poson o e eemens n e perodc abe s reaed

o e ype o cemca bondng a occurs n er

compounds, wc n urn as an efec on e ormuas

and properes o e compounds. he pysca properes

a resu rom dferen ypes o cemca bondng are

more uy dscussed n caper 4 and s soud be

reerred o wen readng s secon.

oXidesofPeriod3

As e number o vaence eecrons ncreases, gong across

e perod ere s a seady ncrease n e number o eecrons avaabe or bond ormaon and ence n e

number o oxygen aoms a eac eemen bonds o. he

ormuas o e ges oxdes o e perod 3 eemens

dspay dsnc perodcy, w eac successve eemen

bondng o an exra a oxygen – Na2O, MgO, A

2O

3,

SO2, P

4O

10(equvaen o P

2O

5), SO

3, C

2O

7.(see Fgure

315 & 316) Oten a e rg o e perodc abe more

an one oxde exss and ese conan e eemen n

dferen oxdaon saes. For exampe posporus can

orm posporus(III) oxde (P4O

6; P n a +3 oxdaon

sae) as we as posporus(V) oxde (P4O

10; P n a +5

oxdaon sae). Smary suur orms suur doxde (SO2;

+4 sae) as we as suur roxde (SO3; +6 sae),wereascorne orms dcorne monoxde(C

2O; +1 sae) and

e exposve corne doxde (CO2

+4 sae), as we as

dcorne epoxde (C2O

7; +7 sae).

he oxdes o e eemens on e et o e perodc abe

(Na and Mg) are oncay bonded and ence are sods

w g meng and bong pons. In e cenre o e

perodc abe scon doxde exss as a gan covaen

ace n wc eac aom s joned o a e oers by

srong covaen bonds. As a resu s a sod w very

g meng and bong pons. To e rg o e

perod, moecuar covaen bondng occurs, so a e

compounds are gases, quds or ow meng pon sods

as a resu o e reavey weak orces a exs beween

e moecues. he moen oxdes o e rs wo eemens

(sodum and magnesum) can conduc owng o e

presence o mobe ons n e qud, bu e oxdes o enon-meas do no conduc n e qud sae. Aumnum

oxde sows caracerscs o bo onc and covaen

bondng. I as an exceponay g meng pon and s

a poor conducor o eecrcy n e qud pase.

he acd-base properes o e oxdes o perod 3 were

descrbed n e prevous secon.

chloridesofPeriod3

he ormuas o e ges cordes o e perod 3

eemens aso dspay a marked perodcy, oug s sno as compee as a dspayed by e oxdes (see Fgure

316). Gong across e perod eac eemen bonds o

one more corne – NaC, MgC2, AC

3(more correcy

wren as A2C

6n s gaseous sae), SC

4and PC

5.

Once agan a e rg and sde oer cordes exs

n wc e eemen as a dferen oxdaon sae, or

exampe PC3

(P n a +3 sae) exss as we as PC5

(P n

a +5 sae).

he cordes o meas, suc as sodum corde and

magnesum corde, are oncay bonded, crysane

sods w g meng pons. Wen added o waer

ese cordes dssove wou cemca reacon, ogve souons n wc e componen ons can beave

ndependeny.

NaC (s) Na+ (aq) + C– (aq)

Even oug aumnum s a mea e beavour o many

o s compounds, especay wen anydrous, s more

ypca o non–meas. hs s a resu o e sma sze and

g carge o e on a aumnum orms. Aumnum

corde or exampe, aoug a sod, submes a e

surprsngy ow emperaure o 178 °C o gve a vapour

conssng many o A2C

6moecues. Wen added o

waer, anydrous aumnum corde undergoes vgorousydroyss (a s spng by e acon o waer) n wc

e bonds beween aumnum and corne are broken

and a songy acdc souon s ormed.

AC3 (s)+ 3H

2O() A(OH)

3 (s)+ 3H+

(aq)+ 3C–(aq)

Even ydraed aumnum corde produces que acdc

souons owng o e dssocaon o e waer moecues

assocaed w e sma, gy carged, A3+ on.

13.1 trends

acrossPeriod3(ahl)

13.1.1 Explain the physical states (under

standard conditions) and the electrical

conductivity (in the molten state) of the

chlorides and oxides of the elements in

period 3 in terms of their bonding and

structure.

13.1 .2 Describe the reactions of chlorine and the

chlorides referred to in 13.1.1 with water.

© IBO 2007

waer

higherleVel

070821 Chem Chap 3.indd 82 6/12/2007 10:51:



Periodicity

83

he gan convaen srucure, ound or e oxdes o e

eemens n e mdde o e perod, s no generay ound

or e cordes because corne usuay orms ony

one bond, makng an exended ace mpossbe. he

cordes o non–meas, suc as scon eracorde and

e cordes o posporus, a ave moecuar covaen

srucures. As a resu o e weak orces beween er

moecues ese compounds ave ow meng and bongpons. Wen added o waer a ydroyss reacon occurs,

n wc e bonds beween e eemen and corne

are repaced by bonds beween e eemen and oxygen.

he resu s an acdc souon conanng ydrogen ons,

corde ons and e oxde, or an oxyacd o e eemen.

For exampe w scon eracorde:

SC4 () + 2 H

2O() SO

2 (s) + 4 H+

(aq) + 4 C–(aq)

In e case o e cordes o posporus, suc as

posporus rcorde (or posporus(III) corde), e

oxyacd ormed aso dssocaes:

PC3 ()+ 3 H

2O() P(OH)

3 (aq)+ 3 H+

(aq)+ 3 C–(aq)

P(OH)3

or H3PO

3s posporc(III) acd; a weak acd a

paray dssocaes as sown:

H3PO

3 (aq) H+

(aq) + H2PO

3–

(aq)

Smary w posporus penacorde (or

posporus(V) corde),

PC5 (s)+ 4H

2O() H

3PO

4 (aq)+ 5H+

(aq)+ 5C–(aq)

H3PO

4s posporc(V) acd; a srong acd a uy

dssocaes as sown beow.

H3PO

4 (aq) H+

(aq) + H2PO

4–

(aq)

Corne se (C2), wc may be regarded as “corne

corde”, s n w s paern o beavour, beng a

moecuar covaen subsance a reacs w waer n an

anaogous ydroyss reacon.

Because o e presence o mobe ons, sodum and

magnesum cordes conduc eecrcy wen moen

or n aqueous souon. he cordes o e remanng

eemens o perod 3 do no conduc eecrcy n e

moen sae, as woud be expeced or moecuar covaencompounds. In aqueous souon owever ey do conduc

eecrcy because o e ons ormed n e cemca

reacons above.

he rends n e properes o e eemens, cordes

and oxdes o e eemens rom sodum o corne are

summarsed n Fgure 316.

Element Na Mg Al Si P S Cl

Bonding MeacGan

covaenMoecuar covaen

Chloride

Formua NaC MgC2

AC3

SC4

PC5

PC3

Compex C2

Bondng Ionc Inermedae Moecuar covaen

Oxide

Formua Na2O MgO A

2O

3SO

2

P4O

10

P4O

6

SO3

SO2

C2O

7

C2O

Bondng Ionc InermedaeGan

covaenMoecuar covaen

Acd/base

properesSo. basc Inso . basc Ampoerc Inso . acdc Soube acdc

Figure 316 The period 3 elements, their chlorides and their oxides

070821 Chem Chap 3.indd 83 6/12/2007 10:51:



CHAPTER 3

84

a h l

1. Gong across e rd perod o e perodc abe,

ere s a seady cange n e ormuae o e oxdes

ormed. Wc one o e oowng oxdes s no anexampe o s rend?

A A2O

3

B Na2O

C SO2

D P4O

10

2. Hydroyss s a reacon n wc

A waer adds on o a moecue.

B waer sps up a moecue.

C waer s a produc.D waer acs as a caays.

3. a) Wen sodum corde s added o waer

e resung souon s a good eecrca

conducor. he same s rue o e souon

ormed wen posporus rcorde s added

o waer, bu or sgy dferen reasons.

Expan s beavour, wrng equaons or

any reacons nvoved.

b) Gven a sampe o e wo souons produced

by addng ese wo cordes o waer

descrbe, gvng e resus a woud beobserved,

a es o sow a bo conaned e

corde on.

a es a woud e wc souon was

ormed rom wc corde.

4. he oxdes o e eemens n e rd perod sow

a rend n acd–base properes gong across e

perod. Coose specc exampes o ree oxdes, one

basc, one ampoerc and one acdc, en use ese

exampes o usrae s rend, wrng baanced

equaons or any cemca reacons nvoved.

5. here s a rend n e cemca caracer o e

eemens n e rd perod (Na o Ar). Descrbe

s brely w respec o e bondng presen n e

eemen and s corde. Expan ese n erms o

rends a occur n aomc properes suc as nucear

carge, onzaon energy and eecronegavy.

Exercise 13.1

he d–block elements are ose a occur n e cenra

bock o e perodc abe, .e e groups eaded by e

eemens scandum o znc, n wc e d–subse o

an aom s beng ed w eecrons. A subse o ese

eemens, known as e transition elements, are ose nwc e eemen as a paray ed d–subeve n one

o s common oxdaon saes.

he eemens o e d–bock are a dense, ard meac

eemens. he eecronc srucures dfer by e addon

o one more d–eecrons or eac successve eemen,

bu noe e wo excepona eecronc srucures o

cromum and copper. In ese eemens ere s ony

one eecron presen n e 4s subeve, w e ‘mssng’

eecron beng presen n e 3d subeve so as o gan

e addona saby assocaed w a a ed and

uy ed d–subeve respecvey. hs agan sows ow

smar n energy e 3d and 4s subeves are.

Snce e 3d eecrons que efecvey sed e ouer 4s

eecrons, e rs onzaon energy remans reavey

consan. As a resu e d–bock eemens ave many

smar cemca and pysca caracerscs. he ease

w wc e 3d eecrons are os decreases as e

nucear carge ncreases, resung n a rend rom e

maxmum oxdaon sae beng e mos sabe a e sar

o e seres o e +2 oxdaon sae beng e mos sabe

a e end. As a resu o er paray ed d–subeve,

e ranson meas ave ceran properes n common,

wc are no generay sared by oer meas (ncudng

Sc and Zn), some o ese are:

• a varey o sabe oxdaon saes

• e aby o orm compex ons

• e ormaon o cooured ons

• caayc acvy

13.2firstrow

d–blockeleMents

(ahl)

13.2.1 List the characteristic properties of transition elements.

13.2.2 Explain why Sc and Zn are not considered

to be transition elements.

© IBO 2007

070821 Chem Chap 3.indd 84 6/12/2007 10:51:



Periodicity

85

VariableoXidationstateshe s–block metals, suc as sodum and cacum, ave

s–eecrons a are easy os, bu e onzaon energes

or e nner eecrons are so g a ese are never os

n cemca reacons, as sown n Fgure 319 or cacum.

For s reason ey aways ave e same oxdaon saes

n er compounds +1 or group 1 and +2 or group 2.

Transon meas ave sgy ger efecve nucear

carges and so er rs onzaon energes are a e

ger, bu ere s no sudden ncrease n successve

onzaon energes n e same way as ere s w e s–

bock eemens (un a e 3d and 4s eecrons ave beenos), as can be seen or cromum n Fgure 319. hs s

because e 3d and 4s eecrons ave smar energes. he

oxdaon sae o ranson meas ereore depends on

ow srongy oxdsng e envronmen s, wc depends

on e presence o speces a ready gan eecrons.

I can be seen by reerrng o Tabe 320, a one o e

mos commony ound oxdaon saes o ranson

meas s e +2 sae wc corresponds o e oss o ewo 4s eecrons. hs s a very sabe sae on e rg o

e d–bock were e g nucear carge ncreases e

dference n energy beween e 3d and 4s eecrons, bu

becomes an ncreasngy poweru reducan gong o e

et. T2+, or exampe, does no exs n aqueous souon

because reduces waer o ydrogen. he second commony

ound oxdaon sae, gong as ar as manganese, s a

wc corresponds o e oss o a e 3d and 4s vaence

eecrons (+3 or Sc; +4 or T ec.). hese are sabe on

e et o e d–bock, bu become ncreasngy poweru

oxdans gong across e perod as e energy requred

o produce ese saes becomes que g (see Fg. 319).

he ges oxdaon saes usuay occur as oxyanons,suc as dcromae(VI) (Cr

2O

72–) and permanganae (aso

reerred o as manganae(VII); (MnO4

–). here are aso a

ew oer commony encounered saes, suc as Cr3+ and

Fe3+, wc do no no s paern. hese common

oxdaon saes are summarsed n Tabe 320.

13.2.3 Explain the existence of variable

oxidation number in ions of transition

elements.

© IBO 2007

Eemen Sc T V Cr Mn Fe Co N Cu Zn

Eecronc

srucure

[Ar]

3d14s2

[Ar]

3d24s2

[Ar]

3d34s2

[Ar]

3d54s1

[Ar]

3d54s2

[Ar]

3d64s2

[Ar]

3d74s2

[Ar]

3d84s2

[Ar]

3d104s1

[Ar]

3d104s2

Decreasing

Increasing

stability of maximum oxidation state

stability of +2 oxidation state

Figure 318 Electronic structure and oxidation state stability of the d-block elements (first row)

I o n i s a t i o n E n e r

g y / M J m o l –

1

Number of electrons lost

1 2 3 4 5 6 7

0

5

10

15

CalciumChromium

Figure 319 The successive ionisation energies of calcium and chromium

070821 Chem Chap 3.indd 85 6/12/2007 10:51:



CHAPTER 3

86

a h l

TOK The historical development of the Periodic Table

Aoug e perodc abe, n s modern orm, s organsed n erms o aomc numbers and eecronc srucure,

orgnaed rom a sudy o e perodcy o cemca properes. No sooner ad eoreca cemsry been pu on a

sound oong n e eary 18 cenury by e recognon o e eemens as undamena budng bocks, roug

e work o Boye, Lavoser and Daon, and e deermnaon o e reave aomc masses o ese, especay by

Berzeus and Cannzzaro, an cemss sared o noce a ceran eemens ad very smar cemca properes.Döberener noced a ree eemens ad smar cemca properes en one eemen oten ad a reave aomc

mass approxmaey md–way beween e oer wo. Exampes o s are L (7), Na (23), K (39) and C (35), Br (80), I

(127). Döberener named ese groups ‘rads’. Newands en noced a every eg eemen, wen paced n order

o ncreasng reave aomc mass, sowed smar cemca properes and reerred o ese as ‘ocaves’. he exampes

gven above n w s as do many oers (noe e nobe gases ad no been dscovered a s dae). here were

owever s many anomaes, or exampe copper was n e same group as sodum and poassum!

he name mos cosey assocaed w e perodc abe s undoubedy a o Mendeéev. He exended and rearranged

Newand’s abe, separang groups no wo subgroups a gave beer correspondence w cemca properes. Anoer

nnovaon was a e et gaps n e abe o mprove e , and predced a eemens woud be dscovered o

ese gaps. he eary ones correspond o e eemens we now know as scandum, gaum and germanum. Mendeéev

gave deaed predcons o e pysca and cemca properes a e expeced ese undscovered eemens o aveand s predcons proved o be remarkaby accurae – a cassc exampe o scenc meodoogy n acon. Mendeéev’s

perodc abe s sown n Tabe 17 beow w s gaps marked by sars (*):

he modern perodc abe s smar o a o Mendeéev, excep a e eemens ave been re–ordered accordng

o aomc number (oerwse argon woud be cassed as an aka mea!), e nobe gases ave been added and e

d– and –bock meas ave been coeced ogeer as separae groups n e cenre o e abe.

Seres Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8

1 H

2 L Be B C N O F

3 Na Mg A S P S C

4 K Ca * T V Cr Mn Fe,Co,N

5 Cu Zn * * As Se Br

6 Rb Sr Y Zr Nb Mo * Ru,R,Pd

7 Ag Cd In Sn Sb Te I

8 Cs Ba Dy Ce * * *

9 * * * * * * *

10 * * Er La Ta W * Os,Ir,P

11 Au Hg T Pb B * *

12 * * * h * U

Figure 317 Mendeléev’s Periodic Table

070821 Chem Chap 3.indd 86 6/12/2007 10:51:



Periodicity

87

Noe a e varey o oxdaon saes ncreases o a

maxmum a manganese and n e second a o e

d–bock ar ewer oxdaon saes are ound because e

greaer nucear carge causes an ncrease n e onzaon

energes o e 3d eecrons. he saby o e a– ed

and uy ed 3d eve (encounered beore n e unusua

eecronc srucures o Cr and Cu) aso afecs e saby

o oxdaon saes. In manganese e +2 sae, wc as

a a ed se ([Ar]3d5), s muc more sabe an e

+3 ([Ar]3d4) sae and e +4 ([Ar]3d3) sae (usuay ony

encounered as manganese(IV) oxde, MnO2), wc are

ereore que srong oxdans. W ron owever ereverse s rue because s e +3 sae a as e a

ed se ([Ar]3d5) and e +2 sae ([Ar]3d6) s que

srongy reducng. In copper, e exsence o e +1 sae

s due o e saby o e ed se ([Ar]3d10). Noe

a because e Cu+ on as a u 3d sub–se, ke Zn2+,

s compounds are no cooured.

theforMationofcoMPleXions

13.2.4 Define the term ‘ligand’.

13.2.5 Describe and explain the formation of

complexes of d–block elements.

© IBO 2007

he ons o d–bock meas and ose n e ower secon

o e p–bock (suc as ead) ave ow energy uned

d– and p–orbas. hese orbas can accep a one par o

eecrons rom speces, known as gands, o orm a davebond beween e gand and e mea on. For exampe an

ammona moecue can donae s non-bondng eecron

par o a copper(II) on.

Sc T V Cr Mn Fe Co N Cu

+7 MnO4

-

+6CrO4

2-

Cr2O

72-

MnO4

2-

+5VO

2+

VO3

-

+4 Ti4+ VO2+ MnO2

+3 Sc3+ T3+ V3+ Cr3+ Fe3+

+2 V2+ Cr2+ Mn2+ Fe2+ Co2+ N2+ Cu2+

+1 Cu+

Increasing stability of +2 state

Increasing stability of maximum state

Figure 320 Common oxidation states of the d–block elements

070821 Chem Chap 3.indd 87 6/12/2007 10:51:



CHAPTER 3

88

a h l

hs beavour, n wc one speces donaes an eecron

par ws anoer acceps , s Lewis acid–basebeavour.

Speces wc conan gands bonded o a cenra mea

on are known as compex ons, a common exampe

beng e deep bue compex on [Cu(NH3)

4]2+ ormed

wen excess aqueous ammona s added o a souon o

a copper(II) sa. Noe a e compex on s wren n

square brackes. he carge s e sum o e carge on

e cenra mea on and e carges on e gands. Forexampe e carge on e [CoC4]2– on s e sum o e

+2 carge on e coba and e our –1 carges on e

corde ons (+2 − 4 = –2).

Ligands are speces a can donae a par o non-bondng

eecrons o e cenra mea on n e compex; e mos

common exampes are waer, ammona, corde on and

cyande on. Mos compex ons ave eer sx gands

arranged ocaedray around e cenra aom (usuay

ound w waer and ammona gands), or our gands

arranged eraedray (usuay ound w corde on

gands), oug some exampes o near compex ons

w a wo gands are ound. hese are usraed n

Fgure 321.

he number o gands around e cenra on s known as

e coordnaon number o e compex on, ence e

coordnaon number o e mea on n e ammne s 2,

n e coroanon s 4 and n e aqua on s 6. he erm

“coordnaon number” aso as a smar use n descrbngcrysa srucures.

Complex ions can ave eer a posve carge (∴ caons)

or a negave carge (∴anons) and ence orm sas w

ons o e oppose carge as usraed n Fgure 322

above. Bo compexes are waer soube and conduc

eecrcy n aqueous souon. Some compex ons are

owever neura because e carge on e mea on and

e gands cance. An exampe woud be [P(NH3)

2C

2].

Beng uncarged s s amos nsoube and beaves as

a moecuar speces. W aqueous sver nrae does

no orm a precpae sowng a n e compex on e

corde ons are srongy bonded o e cenra mea onand are no ree o reac w e sver ons (see aso e

cromum(III) speces n Fgure 324).

he ormaon o compex ons sabses ceran oxdaon

saes and ence afecs e Eo

vaue o e reaed redox

sysem. For exampe e vaue or e [Fe(H2O)

6]+/

[Fe(H2O)

6]2+ coupe s +0.77 V, wereas a or e

Fe(CN)6

3-/ Fe(CN)6

4- coupe s +0.36V, n oer words e

presence o e cyande gand sabses e ron(III) sae.

he ormaon o a compex on can aso ave a major

efec on e coour o a mea on n souon. Aqueous

coba(II) sas, or exampe conan e exaaquacoba(II)

on, wc s a pnk coour. I concenraed ydrocorcacd s added o s, e souon urns bue owng o e

ormaon o e eracorocoba(II) on:

[Co(H2O)

6]2+

(aq) + 4C–(aq) [CoC4]2–

(aq) + 6H2O ()

Pnk Bue

hs s an exampe o a gand excange reacon. For mos

ranson mea ons, suc as coba(II) and copper(II)

M

Cl

Cl

Cl

Cl

M

O O

O

O

H H

H

H H

HH

H

O

H

HO

H

H

Figure 321 Tetrahedral and octahedral complex ions

Compex Ion Carge on

Compex Ion

Oxdaon Sae o

Mea Ion

Smar o

[Cu(NH3)

4]C

2[Cu(NH

3)

4]2+ 2+ +2 CaC

2

[K2(CuC

4)] (CuC

4)2- 2- +2 K

2SO

4

Figure 322 Two compounds of complex ions

070821 Chem Chap 3.indd 88 6/12/2007 10:51:



Periodicity

89

Compex ons exb many ypes o isomerism anaogous

o ose ound w organc compounds. Frsy ere s

ormua somersm (anaogous o srucura somersm)assocaed w wc speces are acng as gands

and ence drecy bonded o e mea on. here are

or exampe ree orms o cromum(III) corde

exaydrae a vary n e way e corde ons are

bonded. Because e bondng o e gand o e mea

on s very sabe n s case, e number o corde ons

presen as ree corde ons can be ound by raon w

aqueous sver nrae. hese somers are summersed n

Fgure 324 beow:

Stereoisomerism aso occurs n compex ons. he smpes

exampes o geomerc somersm occurs n square panarranson mea compexes suc as P(NH3)

2C

2(noe a

as conans P2+, s s an eecrcay neura compex),

wc exss n bo cis– and trans– orms:

Geomerc somersm can aso occur n sx coordnae

ocaedra compexes suc as [Co(NH3)

4C

2]+ dependng

on weer e wo corde gands occupy adjacen (cis)

or oppose (trans) ses.

he gands consdered up o now can ony orm one

bond o e mea on, ey are monodenae gands.

W bdenae gands (.e. ose a can orm wo raer

an one bond o a mea on) suc as damnoeane

gand repacemen akes pace reey n aqueous souon,

bu or oers, suc as cromum(III) and coba(III) eres a sgncan acvaon energy barrer o s, ence

e compex on s unusuay sabe, as or exampe e

cromum(III) compex ons gven n Fgure 324.

Some exampes o common compex ons and er coours

are gven Fgure 323.

isoMerisMincoMPleXions

Formua Coour Amoun o cordeprecpaed by Ag+

(aq)

[Cr(H2O)

4C

2]+C–

•2H2O Dark green 1 mo

[Cr(H2O)

5C]2+(C–)

2•H2O Lg green 2 mo

[Cr(H2O)

6]3+(C–)

3Grey–bue 3 mo

Metal ionWaer

Ocaedra

Ammona

Ocaedra/Sq. panar

Corde on

Teraedra

Coba(II)Pnk

[Co(H2O)

6]2+

Sraw

[Co(NH3)

6]2+

Bue

[CoC4]2−

Ncke(II)Green

[N(H2O)

6]2+

Bue

[N(NH3)

6]2+

Yeow-green

[NC4]2−

Copper(II)Bue

[Cu(H2O)

6]2+

Deep bue

[Cu(NH3)

4]2+

Yeow

[CuC4]2−

Figure 323 Some common complex ions and their colours

Figure 324 Isomers of hydrated chromium(III) chloride hexahydrate

Pt

H3N Cl

NH3Cl

trans–complex

Pt

H3N Cl

H3N Cl

cis

–complex

Figure 325 cis- and trans- forms

070821 Chem Chap 3.indd 89 6/12/2007 10:51:



CHAPTER 3

90

a h l

In an soaed aom a o e d–orbas ave exacy

e same energy, bu an aom or on s surrounded by

carged ons or poar moecues, e efec o e eecrc

ed rom ese as a dferen efec on e varous d–

orbas. Because o er symmery e orbas are oten

sp up no wo dferen groups. For ocaedra compexons ree orbas are a ow energy and wo orbas a

ger energy. he dference n energy beween ese wo

groups o orbas vares sgy w e naure o e

speces surroundng e mea on, bu e requency o e

g correspondng o s (nked by e ormua ∆E = h.f )

occurs n e vsbe regon. hs means a wen we

g passes roug a compound o a ranson mea,

g o a parcuar requency s absorbed and an eecron

s promoed rom a ower energy orba o a ger energy

orba, as sown n e Fgure 327 beow.

he g a passes roug ereore appears cooured

because some o e requences ave been absorbed.

In e case o mos copper(II) compounds, red and

yeow g are absorbed so a ey ook a bue–green

coour, a s. we see e ransmed g wc s e

compemenary coour o e absorbed g. he exac

sade depends sgy on e speces surroundng e

copper, so a e exaaquacopper(II) on s g bue

bu e eraammnecopper(II) on s dark bue.

I ere are no eecrons n e d–orbas, as s e case

or Sc3+ and T4+, en ere are no d-eecrons o move

and e compounds are coouress. I e d–orbas are a

compeey ed, as s e case w Zn2+, en ere are

no vacan orbas or e eecrons o move no and agan

e compounds are coouress.

(H2N–CH

2–CH

2–NH

2sown as N N beow) non–

supermposabe mrror mage orms can occur, gvng

rse o enanomersm. An exampe s e compex on

[Co(H2N–CH

2–CH

2–NH

2)

3]3+, sown beow:

colouredions

13.2.6 Explain why some complexes of d–block

elements are coloured.

© IBO 2007

13.2.7 State examples of the catalytic action of

transition elements and their compounds.

13.2.8 Outline the economic significance of catalysts in the Contact and Haber

processes.

© IBO 2007

catalyticactiVity

he caayc beavours o transition metals and er

ons are many caused by a combnaon o wo properes

aready menoned. Frsy ey orm compex ons w

speces a can donae one pars o eecrons. hs resus

n cose conac beween e dferen gands, as we asbeween e mea and e gand. Secondy ranson

mea ons ave a wde varey o reavey sabe oxdaon

saes, so ey can ready gan and ose eecrons n redox

reacons.

d–bock eemen caayss can eer be eerogeneous

or omogeneous, oug e ormer are more common.

Many enzymes nvoved n caaysng redox reacons aso

conan ranson mea ons near e acve se (reer

o Caper 13). In a eerogeneous caays e surace

o e mea or compound provdes an acve surace on

wc e reacon can occur w a reduced acvaon

energy. A common exampe o eerogeneous caayss s

Co

N N

N N

N

N

Co

N N

N N

N

N

3+3+

Figure 326 The two enantiomers of the complex ion

[Co(H 2N–CH

2–CH

2–NH

2 )

3 ]3+

↑↓ ↑ ↑↓ Energy gapcorresponds to

visible lightfrequencies

Light absorbed

as electron promoted E n e r g y

↓↑↓↑ ↓↑ ↓↑↓↑ ↑

↓↑

Figure 327 The interaction between transition metal ions and light

070821 Chem Chap 3.indd 90 6/12/2007 10:51:



Periodicity

91

manganese(IV) oxde wc caayses e decomposon

o ydrogen peroxde o waer and oxygen.

2H2O

2(aq) 2H

2O() + O

2(g)

Anoer exampe s ncke caaysng e reacon beween

ydrogen and an akene o produce an akane.

C C H2

Ni

C

H

+ C

H

(g) (g)(g)

Figure 328 Production of an alkane

Here bondng o e mea surace no ony brngs e

moecues no cose conac, bu aso eecrons rom e

bonds are used o bond o e mea aoms. hs weakens

e bonds n e moecues and owers e acvaonenergy.

Panum and paadum are ound n e caayc

converers ed o e exaus sysems o cars o reduce

e emsson o pouans suc as carbon monoxde and

oxdes o nrogen, e.g.

2 CO + 2 NO 2 CO2

+ N2

Many oer mporan ndusra caayss nvove

ranson meas, suc as ron n e Haber process and

vanadum(V) oxde n e Contact process.

Haber process: N2(g) +3H

2(g) 2NH

3(g)

Conac process: 2SO2(g) + O

2(g) 2SO

3(g)

he economc mporance o e cemca ndusry ress

on e ood, coes, medcnes and e grea varey o

consumer arces a produces. One o e sgns o

e economc deveopmen o a counry s e sae o s

cemca ndusry because e cemca ndusry can ake

essenay smpe and oten ceap raw maeras and urn

em no muc more vauabe producs. For exampe, e

Haber process wc expos e ‘ree’ suppy o nrogen

( s coss money o exrac e nrogen) rom eamospere and convers no ammona and en no

exposves upon wc wars and conlcs ave become

dependen (e commercazaon o s process key

proonged Word War I by a eas one year). I s aso

va n e producon o erzers a are now va or

our suppy o ood. Nrogen s an eemen va or pan

grow, so e major use o ammona s n e manuacure

o erzers suc as ammonum sas and urea. I s aso

used n e manuacure o nrogen conanng poymers

suc as nyon.

Suluric acid s consdered e “kng o cemcas” and s

reavey easy o produce. Suurc acd as numerous uses

n e cemca ndusry – ndeed e onnage o used

annuay gves a good ndcaon o e exen o a counry’s

cemca ndusry. hese uses ncude manuacure o erzers (especay converng nsoube pospae rock

o soube ‘superpospae’), poymers, deergens, pans

and pgmens. I s aso wdey used n e perocemcas

ndusry and n e ndusra processng o meas. One

o s mnor, oug possby mos amar uses, s as e

eecroye n auomobe baeres.

In omogeneous caayss, e caays s n e same pase

as e reacans. In ese reacons a parcuar mea

on s oxdsed n one sage and en reormed by beng

reduced n a second sage. A good exampe s e roe

o ron(II)/(III) n caaysng e sow reacon beweenacded ydrogen peroxde and odde ons. he ron(II)

s oxdsed by e peroxde o ron(III).

H2O

2(aq) + 2H+

(aq) + 2Fe2+(aq) 2H

2O () + 2Fe3+

(aq)

hs s en reduced by e odde ons o reorm ron(II).

2I–(aq) + 2Fe3+

(aq) I2

(s) + 2Fe2+(aq)

hese reacons occur more rapdy an e drec reacon

because ey bo ave ower acvaon energes an e

drec reacon.

Exampes o enzymes conanng ranson meas

ncude e presence o ron n eme, e acve par o

aemogobn responsbe or carryng oxygen n e

bood, and o coba n vamn B12 wc s va acor

n e producon o red bood ces as we as avng oer

uncons. he srucures o ese wo enzymes are gven

n Fgures 329 and 330.

MnO2

Pd/P

Fe

V2O5

070821 Chem Chap 3.indd 91 6/12/2007 10:51:



CHAPTER 3

92

e X t e n s

i o n

Titanium as an eecronc srucure [Ar] 3d2 4s2.

Tanum s acuay a componen o a number o quecommon mneras. I s owever reavey dicu o

exrac rom ese, ence e g prce o e mea.

Nevereess because o s ow densy, g sreng

and corroson ressance nds wdespread use n e

aerospace ndusry. Is mos common oxdaon sae

n compounds s e +4 sae and, as anum doxde

(ound nauray as rue), nds wdespread use as a

we pgmen n pan and cosmec producs. he easy

ydroysed eracorde s empoyed as a caays n e

Zeger-Naa poymersaon o akenes. Tanum(III)

ons, produced by reducng anum(IV) compounds

w znc, are poweru reducans n aqueous souonand anum(II) s so poweruy reducng w reduce

waer o ydrogen.

Vanadium as an eecronc srucure [Ar] 3d3 4s2 and

can exs n a varey o oxdaon saes rom +2 o +5,

e ger ones exsng as varous oxy-ons. For exampe

vanadum(V) can exs as VO2

+ and VO3

–, as we as e

more amar vanadum(V) oxde (V2O

5, used as a caays

n e Conac process). I znc s added o an acdc

souon o e yeow vanadae(V) on (VO3

–) a noabe

seres o coour canges ake pace as s reduced rsy

o bue vanadum(IV), en o green vanadum(III) and

nay o e avender cooured vanadum(II). hese oweroxdaon saes are graduay more poweru reducans.

Chromium as an eecronc srucure [Ar] 3d5 4s1 (n.b.

ke copper an excepon n ony avng one 4s eecron).

Is common oxdaon saes are +3 and +6. Compounds o

cromum(III), suc as cromum(III) oxde, Cr2O

3, and

e exaaquacromum(III) on, [Cr(H2O)

6]3+, are usuay

a dark green coour. Dark green cromum(III) ydroxde

s precpaed wen aqueous aka s added o souons

o cromum(III) sas. Lke aumnum ydroxde, s

ampoerc and redssoves n g concenraons o

ydroxde ons o gve a dark green souon conanng

e cromae(III) on (aso caed crome):

Cr3+(aq) + 3OH–

(aq) Cr(OH)3(s)

Cr(OH)3

(s) + OH–(aq) Cr(OH)

4–

(aq)

he common compounds o cromum(VI) are e dark

red–brown oxde, CrO3

– wc n many ways resembes

SO3, as we as e yeow cromae(VI), CrO

42–, and

orange dcromae(VI), Cr2O

72–, ons derved rom .

thecheMistryofindiVidual

transitionMetaleleMents

eXtension

Figure 329 The structure of a heme group from

cytochrome oxidase

Figure 330 The structure of Vitamin B12

070821 Chem Chap 3.indd 92 6/12/2007 10:51:



Periodicity

93

2CrO3(s) + H

2O() 2H+

(aq) + Cr2O

72–

(aq)

he cromae(VI) and dcromae(VI) ons are n an acd–

base equbrum. I acd s added o e yeow cromae,

en e equbrum sts o e rg o gve e orange

dcromae. hs cange can be reversed by addng an

aka:

2 H+(aq) + 2 CrO

42–

(aq) Cr2O

72–

(aq) + H2O()

Yeow Orange

he dcromae(VI) on s a srong oxdan n acdc

souon, beng reduced o e green cromum(III) on:

Cr2O

72–

(aq) + 14 H+(aq) + 6 e– 2Cr3+

(aq) + 7 H2O()

Orange Green

Manganese as an eecronc srucure [Ar] 3d5 4s2. Is

common oxdaon saes are +2, +4, +6 and +7. he mos

common manganese(VII) compound s e permanganaeon (or manganae(VII) on), MnO4

–, wc as a very

nense purpe coour. I s a very poweru oxdan and

e oer common oxdaon saes can be ormed by s

reducon under varous condons, dependng on e

pH a wc e reacon occurs. In very srongy akane

condons, e dark green manganae(VI) on s e

produc:

MnO4

–(aq) + e– MnO

42–

(aq)

In approxmaey neura souon, a brown precpae o

manganese(IV) oxde orms:

MnO4–

(aq) + 4H+(aq) + 3e– MnO2

(s) + 2H2O ()

In acdc souon e amos coouress (n concenraed

souon, very pae pnk) manganese(II) on s e produc.

hs reacon s requeny used n raons o deermne

e concenraons o easy oxdsed speces, suc as

SO3

2−and Fe2+.

MnO4–

(aq) + 8H+(aq) + 5e– Mn2+

(aq) + 4H2O

()

Manganese(IV) oxde s se a poweru oxdan, or

exampe oxdsng concenraed ydrocorc acd o

corne:

MnO2(s) + 4 HC(aq) MnC2(aq) +2 H2O() + C2(g)

I s mos commony encounered because o s aby o

caayse e decomposon o ydrogen peroxde.

Wen aqueous aka s added o souons o manganese(II)

sas a les cooured precpae o manganese(II) ydroxde

s ormed. hs rapdy darkens n e presence o ar as

manganese(II) ydroxde s oxdsed o manganese(III)

ydroxde by oxygen n aqueous souon:

Mn2+(aq) +2OH–

(aq) Mn(OH)2

(s)

4Mn(OH)2(s)+ 2H2O

()+ O2(g) 4Mn(OH)3

(s)

Iron as an eecronc srucure [Ar] 3d6 4s2. Is wocommon oxdaon saes are +2 and +3. Iron(II)

compounds are usuay pae green n coour. Iron(III)

compounds usuay vary rom yeow o brown n coour.

he wo oxdaon saes are ready nerconvered

(Eѳ = 0.77 V) so a ron(II) acs as a md reducan and

ron(III) as a md oxdan:

Fe3+(aq) + e– Fe2+ (aq)

Oxygen n e ar w oxdse ron(II) o ron(III), e

ger e pH e aser e reacon. As a resu ron(II)

compounds are oten conamnaed w races o ron(III).

he oxdaon sae o ron n aqueous souon can be

ready deeced by addng aqueous aka un a precpae

o e ydroxde orms. Iron(II) ydroxde s green, oug

urns brown on sandng as a resu o aera oxdaon

(smar o a o manganese(II) ydroxde above oug

e reacon s raer sower), and ron(III) ydroxde s

red–brown:

Fe2+(aq) + 2OH–

(aq) Fe(OH)2

(s)

Green precpae

Fe3+(aq) + 3OH–

(aq) Fe(OH)3(s)

Red–brown precpae

Wen ocyanae (SCN–) ons are added o a souon

o an ron(III) compound an nense bood–red cooured

compex on s ormed. Iron(II) sas, pure, gve no

reacon. he major reacon s a sown beow, oug

urer gand excange s possbe and e precse produc

w depend on e concenraon o ocyanae ons.

[Fe(H2O)

6]3+ + SCN− [FeSCN(H

2O)

6]2+ + H

2O

Cobalt as an eecronc srucure [Ar] 3d7 4s2 and sused n a varey o sees. Is mos sabe oxdaon sae

s e +2 sae, wc n due aqueous souon exss as

e pnk [Co(H2O)

6]2+ on. Addng aqueous aka o s

souons precpaes ou e ydroxde, wc oug

nay bue, sowy canges o a pnk coour:

Co2+(aq) + 2OH–

(aq) Co(OH)2

(s)

Bue, en pnk precpae

070821 Chem Chap 3.indd 93 6/12/2007 10:52:



CHAPTER 3

94

e X t e n s

i o n

Wen concenraed ydrocorc acd s added o souons

conanng e exaaqua coba(II) on e coour graduay

canges rom pnk roug sades o purpe, evenuay

yedng e deep bue eracoro on:

[Co(H2O)6]2+(aq) + 4 C–(aq)

[CoC4]2–(aq)+ 6 H2O() Pnk

Bue

he coba(III) sae aso exss bu s generay a poweru

oxdan, oxdsng waer o oxygen n aqueous souon.

Ammona gands owever sabse e coba(III) sae

so a wen aqueous ammona s added o coba(II)

compounds e sraw cooured souon, ormed wen

e na green precpae redssoves, graduay darkens

as dssoved oxygen oxdses e coba(II) exammne

compex o e coba(III) exammne compex.

4 [Co(NH3)6)]2+ + O2 + 2 H2O

4 [Co(NH3)6)]

3+

+ 4 OH

−

In e presence o corde ons s aso possbe o produce

an neresng varey o somers, smar o ose gven n

Fgure 324 or compex ons conanng cromum(III)

w corde and waer gands, a are knecay sabe

o gand excange reacons.

Nickel as an eecronc srucure [Ar] 3d8 4s2 and s ony

sgncan oxdaon sae s e +2 sae ormed by e

oss o e wo 4s eecrons. he mea s wdey used n a

varey o sees and n aoys used o make cons. Ncke(II)

compounds are generay pae green and n aqueous

souon exs as e green exaaqua on, [N(H2O)6]2+

.hs precpaes ou e pae green ncke(II) ydroxde

wen aqueous aka s added:

N2+(aq) + 2 OH–

(aq) N(OH)2(s)

Pae green

I ammona s added e na precpae ready

redssoves o orm a a pae bue souon conanng e

exaammne compex:

[N(H2O)

6]2+

(aq) + 6 NH3(aq)

[N(NH3)

6]2+

(aq) + 6 H2O() Green

Pae bue

Copperas an eecronc srucure [Ar] 3d10 4s1 (agan noe

a s s an excepon, avng ony one 4s–eecron). he

mos common oxdaon sae o copper s e copper(II)

sae. Copper(II) compounds are usuay bue cooured

oug some, suc as e carbonae, are green and bo

copper(II) oxde and copper(II) sude are back. Mos

copper(II) compounds are waer soube ormng e pae

bue exaaquacopper(II) on, bu s s ready convered

no oer compex ons. Addng concenraed ydrocorc

acd produces e yeow eracorocopper(II) anon.

Addng aqueous ammona, nay produces a pae

bue precpae o copper(II) ydroxde, bu s ready

redssoves n excess o e reagen o gve a dark bue

souon conanng e eraammnecopper(II) caon:

[Cu(H2O)6]2+(aq) + 4 C–(aq) [CuC

4]2–

(aq) + 6 H2O() Pae bue

Yeow

[Cu(H2O)

6]2+

(aq) + 4 NH3(aq)

[Cu(NH3)

4(H

2O)

2]2+

(aq) + 4 H2O() Pae bue

Dark bue

he reacon o precpae bue copper(II) ydroxde aso

occurs wen oer aqueous akas are added o souons

o copper(II) sas:

Cu

2+

(aq) + 2OH

–

(aq) Cu(OH)2(s)

Copper can aso exs n a +1 oxdaon sae. hs sae as

a compeey ed d– subse (ke Ag+ and Zn2+), so a

mos o s compounds are coouress. he on s unsabe

n aqueous souon ormng copper mea and copper(II)

ons:

2 Cu+(aq) Cu(s) + Cu2+

(aq)

Noe a n s reacon e copper(I) s smuaneousy

oxdsed and reduced. Reacons o s ype are known as

dsproporonaon reacons.

Insoube copper(I) sas are sabe owever, e mos

common beng copper(I) odde, wc s a we sod

ormed by e reducon o copper(II) compounds w

odde ons. he odne, ormed a e same me, can be

removed by addng excess aqueous osuae.

2 Cu2+(aq) + 4 I–(aq) 2 CuI(s) + I2 (aq)

Copper(I) oxde s a red–brown sod a s ormed

wen copper(II) compounds are reduced under akane

condons, or exampe n Feng’s souon were arrae

ons compex e copper(II) ons o preven copper(II)

ydroxde precpang:

2Cu2+(aq) + 2OH–

(aq) + 2e– Cu2O (s) + H2O ()

Transon meas orm a number o reavey sma gy

carged ons, suc as Cr3+ and Fe3+. In aqueous souon

e waer gands o ese ydraed ons dssocae o make

e souon acdc, n a smar way o A3+.

[M(H2O)

6]3+

(aq) [M(H2O)

5OH]2+

(aq) + H+(aq)

070821 Chem Chap 3.indd 94 6/12/2007 10:52:



Periodicity

95

1. he oxdaon sae a occurs or e greaes

number o rs row ranson meas s

A +1B +2

C +3

D +4

2. he g oxdaon saes o ranson meas are

A usuay ound o e rg and sde o

e ranson seres.

B usuay ound o nvove smpe ons.

C usuay poweru oxdans.

D usuay coouress.

3. Transon mea ons are requeny cooured

because

A ey absorb nrared radaon and

re–em as vsbe g.

B o e vbraons o e gands

surroundng em.

C o e movemen o eecrons beween

d–orbas.

D g causes em o sponaneousy

cange er oxdaon sae.

4. he coour o e compex on ormed beweencoba(II) ons and excess corde ons s

A green.

B yeow.

C pnk.

D bue.

5. Wc one o e oowng eemens s no cassed

as a ranson mea?

A Cu

B Zn

C MnD T

Exercise

6. Expan brely wy

a) Poassum aways occurs as a +1 on n s

compounds and cacum as a + 2 on, bucompounds o manganese are known n

wc e oxdaon sae o e manganese

vares rom +2 o +7.

b) here s a sg cange n e sade o green

o an aqueous souon o ncke(II) suae,

wen concenraed ydrocorc acd s

added.

c) Ammona orms compex ons w coba(II)

ons, bu meane does no.

7. Descrbe wa woud be seen durng e oowng:

a) A ew drops o aqueous ammona are added

o aqueous copper(II) suae and en a arge

excess s added.

b) Suur doxde gas (a srong reducng agen)

s bubbed roug acded poassum

dcromae(VI).

c) Aqueous ron(II) suae s warmed w

excess aqueous ydrogen peroxde and en

aqueous sodum ydroxde s added o e

produc.

d) Sod manganese(IV) oxde s added o

aqueous ydrogen peroxde.

8. Caayss conanng ranson meas or er

compounds, are mporan n many ndusra

processes. Coose two exampes o s and n eac

case:

a) Name e caays.

b) Wre a baanced equaon or e reacon

a caayses.

Expan e dference beween omogeneous and

eerogeneous caayss and sae wc caegory

your cosen exampes beong o.

070821 Chem Chap 3.indd 95 6/12/2007 10:52:



CHAPTER 3

9. Gve e ormuaes o e compex on(s) or

oxyanon(s) o e rs row o d–bock eemens (Sc

o Zn) correspondng o eac o e oowng:

a) A bue souon a urns green en yeow

wen concenraed ydrocorc acd s

added.

b) he on ormed wen excess aqueousammona s added o aqueous copper(II)

suae.

c) A bue souon a urns pnk wen waer s

added o .

d) An orange souon a urns yeow wen

aka s added o .

e) A purpe souon a goes dark green wen

concenraed aka and a reducan are

added.

10. he cyande on (CN–) can orm wo compex ons

w ron ons. he ormuae o ese are Fe(CN)6

4–

and Fe(CN)6

3–.

a) Wa sape woud you expec ese o ave?

b) Wa s e oxdaon sae o e ron n e

wo compex ons?

c) Wa eaure o CN– aows o orm

compex ons w ranson meas?

11. Accoun or e oowng observaons:

a) T2+ w reduce waer o ydrogen, bu Ca2+

w no.

b) V3+ compounds are cooured bu Sc3+

compounds are no.

c) V3+ can ac as bo an oxdsng agen and a

reducng agen, ws Sc3+ s neer.d) Cu+ as coouress compounds bu Cu2+

compounds are cooured.

e) Co(NH3)

3C

3exss n a number o somerc

orms.

12. he compex on [Co(H2NCH

2CH

2NH

2)

2C

2]+ s

ocaedra and exss as wo dferen geomerc

somers.

a) Draw ese somers so as o usrae ow e

geomerc somersm arses.

One o ese wo somers can aso exs n wo

enanomerc orms.

b) Draw ese somers so as o usrae ow

e enanomersm arses and expan wy.

enanomers o e oer geomerc somer

do no occur.

c) Name a vamn a conans coba and sae

a meaboc uncon o s vamn.

chapter 03 periodicity

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