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Learning outcomes

Describe the periodicity of elementsacross period 3 and down groups 1and 17 for the following physical

properties:i. metallic character

ii. melting point

iii. boiling point

Describe and explain the acid-basecharacter of oxides of elements inperiod 3.

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Physical Properties

down the Groups 1 and 17

i) Metallic character (group 1 & 17)

Metallic character is closely related to

atomic radius and ionization energy.

The easier it is to remove electrons from anatom, the more metallic the element.

Easy removal of electrons corresponds to

large atomic radius and low ionizationenergy.

Metallic character increases down a group

and decreases across a period of the

periodic table.

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General properties of group 1

elements

All elements in group 1 are reactive

metals

Melting and boiling points of group 1:

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Going down the group, the melting

and boiling points of the elements

decrease.

-As we go down the group, the size

of atoms increases; which causedthe electron to be less attracted to

the nucleus. Therefore the metallic

bond is weaker as we go down thegroup.

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GROUP 1 Common pyhsical properties :

High lustre, good thermal and

electrical conductivity. Soft

Relatively low density

Low melting points

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Element Ionic

radius/pm

First IE

(kJ/mol)

Melting

point (oC)

Boiling

point (oC)

Li 60 520.1 180 1327

Na 95 495.8 97.8 883

K 133 418.8 63.7 756

Rb 148 402.9 39 688

Cs 169 375.6 28.6 690

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Down the group: IE decrease

Size of atom increase

Metallic character increase

Oxidation state = +1

Good reducing agent

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Properties of Halogens

All the halogens exist as diatom, X2.

They have valence electrons with the

configuration of ns2np5. This allows them to form covalent

bond between atoms in order to

achieve noble gas configuration.

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Their physical properties change gradually aswe go down the group.

Descending a group, the melting and boiling

points increase.

This is related to the increasing strength of vander Waals forces with increasing size or relative

molecular mass.

Thus, F and Cl are gases, Br is a liquid and I is a

solid

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GROUP 17

Exists as covalent non-polar molecules

Molecular formula, X2

Element Physical state at room

temperature

Boiling

point (oC)

Melting

point (oC)

F2 Light green-yellow gas -188 -233

Cl2 Green gas -35 -103

Br2 Dark red-brown liquid 59 -7.2

I2 Steel-grey solid,

sublimes to a violet

vapour

184.4 113

VIDEO 3
http://localhost/var/www/apps/conversion/tmp/scratch_10/4L6%20V3E.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_10/3L6%20V3.SWFhttp://localhost/var/www/apps/conversion/tmp/scratch_10/4L6%20V3E.htmhttp://localhost/var/www/apps/conversion/tmp/scratch_10/3L6%20V3.SWF

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6) Periodic trends in the melting /

boiling point

The melting / boiling point of a

substance depends greatly on thetype of intermolecular forces or

bondings involved.

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Melting and boiling point of

elements in period 3

Element Na Mg Al Si

Melting

point (oC)

97.8 651 660 1410

Boiling

point (oC)

892 1107 2467 2680

P S Cl Ar44 119 -101 -189

280 445 -34.5 -186

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Variation of melting and

boiling point of elements in

period 3 can be discussed in 3 parts:

a) Metallic structure (Na to Al)

Metallic crystals have positive metal ions

attracted by electrons in a cloud -metallic

bonding.

VIDEO 1

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The more

valence

electrons,

the stronger

the metallic

bonding andthe

melting /

boiling point

Strength of metallic bonding is

proportional to the number of valence

/ delocalized electrons.

Na-1 valence electron

Mg-2 valence electronsAl- 3 valence electrons

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Each silicon is tetrahedrally bonded to other 4

silicon atoms with stong covalent bond.

The result is a crystal that is essentially one

gigantic / network molecule.

Melting and boiling point of Si is very high

because of the strong attractions between

covalently bonded atoms. High energy is needed to break the strong

covalent bonding in melting or boiling.

b) Gigantic molecular structure (Si)

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Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

Si

Covalent bond

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These are mainly the non-metal that existas molecules of P4, S8, Cl2 and Ar

(monoatom).

The covalent bond between the atoms isvery strong but the intermolecular force,that is, London dispersion force (Van derWaals), is very weak.

c) Simple molecular structure ( P to Ar)

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S

S

S

S

S

S

S

S

S8 (m.p = 119 C)

P

P

PP

P4

m.p = 44Cb.p = 280C

ArCl2 Cl2

Weak Van Der Waals forces

Cl2

(m.p= -101 C)

Ar (m.p = -180 C)

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van der Waals force is proportional

to molecular size (relative molecular

weight)

Molecular size:

Ar < Cl2 < P4 < S8

therefore melting / boiling point :

Ar < Cl < P < S

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Acid-base behavior of oxides

of Period 3

For Period 3:

Na Mg Al Si P S Cl Ar

basic amphoteric acidic

VIDEO 2

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Na react with oxygen to form basic oxide.

The oxide will produce base when react

with water.

4Na (s) + O2 (g) 2Na2O (s)

Na2O (s) + H2O (l) 2NaOH (aq)

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Mg burn in oxygen to form basic oxide,MgO.

2Mg (s) + O2

(g) 2MgO (s)

MgO (s) + 2HCl (aq) MgCl2 (aq) + H2O (l)

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Al forms amphoteric oxide, oxide

that can react with either an acid ora base.

Al2O3 (s) + 6HCl (aq) 2AlCl3 (aq) + 3 H2O (l)

base acid

Al2O3 (s) + 2NaOH (aq) + 3H2O (l) 2NaAl(OH)4 (aq)

acid base sodiumaluminate

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Silicon burn in oxygen to form acidic

oxide.

Si (s) + O2 (g) SiO2 (s)

SiO2 (s) + 2OH- (aq) SiO3

2- (aq) + H2O (l)

acidic

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P4 (s) +3O2 (g) P4O6 (s)

P4O6 (g) + 6H2O (l) 4H3PO3 (aq)

phosphorus acid

P4O10 (g) + 6H2O (l) 4H3PO4 (aq)

phosphoric acid

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S (s) + O2 (g) SO2 (g)

SO3 (g) + H2O (l) H2SO4 (aq)

SO2 (g) + 2NaOH (aq) Na2SO3(aq)+H2O(l)

acid base

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Cl2O7 (g) + H2O (l) 2HClO4 (aq)hypochloric acid

Halogens react indirectly with oxygen

to form oxides. Oxides of chlorine existin the compounds of Cl20, ClO2 and Cl207

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The properties of oxides of Period

3 elements

Element Na Mg Al Si P S Cl

Formula

of oxides

Na2O MgO Al2O3 SiO2 P4O6P4O10

SO2SO3

Cl2O

ClO2

Cl2O7

Chemical

Props.

Basic oxides Amph

oteric

Unrea

ctive

Acidic oxides

Molecularstructure

Ionic compounds Giantnetwor

k

Molecular covalentcompounds

m.p High High Relatively low

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Conclusion

Physical properties of elements Metallic character

Melting point

Boiling pointDown a group 1 and 17

Across a period 3

Behavior of oxide in period 3-metal, amphoteric and non-metal

4.6 pt

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