Chapter 7

7.2 Effective Nuclear Charge

7.3 Size of Atoms & Ions

7.4 Ionization

7.5 Electron Affinity

7.1 PERIODIC TRENDS

• Arises from the Periodic patterns in

ELECTRON CONFIGURATIONS.

• Elements in the same GROUP have the

same number of VALENCE electrons

• VALENCE electrons = electrons in the

outermost orbital

7.2 EFFECTIVE NUCLEAR CHARGE

The NET positive charge experienced by an electron.

Core electrons pulled in tightly

Valence electrons held less tightly

Shielding effect reduces the full nuclear charge of outer electrons

7.2 Effective Nuclear Charge

BASED On The PERIODIC

RECURRENCE Of PROPERTIES

Periodic Trends In

7.3 Sizes of atoms and ions.

7.4 Ionization energy.

7.5 Electron affinity.

7.3 Sizes of atoms

As we move down a group, the atoms become larger. Due to INCREASING value of n

7.3 SIZES OF ATOMS

BUT !!

As we move ACROSS ACROSS ACROSS ACROSS a period, {left to right}

atoms become SMALLERSMALLERSMALLERSMALLER

WHY ?

As we move ACROSS the periodic table, the number of core electrons remains constant, but the nuclear charge increases

Which of the following ATOMSATOMSATOMSATOMS is largest

N , O , F

S or O

Na , Mg , Al

Na or Cl

Na or K

?

?

?

?

?

• CATIONSCATIONSCATIONSCATIONS lose electrons and are

SMALLER THAN THE PARENT IONSMALLER THAN THE PARENT IONSMALLER THAN THE PARENT IONSMALLER THAN THE PARENT ION.

• ANIONSANIONSANIONSANIONS add electrons and are

LARGER THAN THE PARENT IONLARGER THAN THE PARENT IONLARGER THAN THE PARENT IONLARGER THAN THE PARENT ION.

Ions INCREASE

in size as you go

down a column.

Due toINCREASING

value of n.

Sizes of Cations

Sizes of Anions

ISOelectronic series

A group of ions all containing the same number of electrons

How many electrons do

O2- ; F- ; Na+ ; Mg2+ and Al3+ have ?

10

-- Increasing nuclear charge �

O2- > F- > Na+ > Mg2+ > Al3+

--- Decreasing ionic radius �

In an isoelectronic series

Ionic size decreases with

an increasing nuclear charge

{See Text page 269}

Which of the following is largest ?

• Na or K ?

• Na or Mg ?

• S2– or O2– ?

• S2–, S, or O2– ?

• K+, Cl–, Ca2+, or S2– ?

• O 2- , F - , Na + , Mg 2+ , or Al 3+

Arrange the ions K+, Cl–, Ca2+, and S2– in order of DECREASING size.

These form an isoelectronic series of ions

Size decreases as the nuclear charge of the ion increases.

The atomic numbers of the ions are S (16), Cl (17), K (19), and Ca (20)

Arrange O 2- , F - , Na + , Mg 2+ , Al 3+

according to size

As nuclear charge increases in an

isoelectronic series the ions become

smaller

7.4 IONIZATION ENERGY

Measure Of How Tightly

An ELECTRON

Is HELD

By The NUCLEUS

IONIZATION ENERGY

How Much ENERGY is Required To

REMOVE An ELECTRON From

An ATOM In Its GROUND STATE

for example

H ���� H + + e-

Periodic Trends in Ionization Energies

Ionization energy decreases going

down a group

Ionization energy generally increases

across a period.

Ionization energy decreases down a group

• The outermost electron is more readily

removed as we go down a group.

Why ?

The further the electron is from the nucleus

the less tightly it is held

Ionization energy generally increases across a

period.

As we move across a period, Zeff increases.

Therefore, it becomes more difficult to

remove an electron.

Electron Configuration of Ions

Cations: electrons removed from orbital with

highest principle quantum number, n, first:

Li (1s2 2s1) ⇒ Li+ (1s2)

Fe ([Ar]3d6 4s2) ⇒ Fe3+ ([Ar]3d5)

Anions: electrons added to the orbital with

highest n:

F (1s2 2s2 2p5) ⇒ F- (1s2 2s2 2p6)

Ionization Energy & Electron Affinity

Ionization Energy change accompanying

loss of electron Na → Na+ + e−

Electron Affinity Energy change accompanying addition of electron

Cl + e− → Cl−

7.5 Electron Affinities7.5 Electron Affinities

• Electron affinity is the opposite of ionization energy

• Electron affinity is the energy change when an atom gains an electron

Cl(g) + e- →→→→ Cl-(g)

ELECTRON AFFINITY

THE ENERGY CHANGE

THAT OCCUR WHEN

AN ELECTRON IS ACCEPTED

BY AN ATOM

Cl + e- ���� Cl -

CLASSIFICATION

BASED ON SUBSHELL BEING FILLED

Representative Elements (s & p electrons)

a) ALKALI Metals

b) ALKALINE EARTH Metals

Transition Elements (d electrons)

Lanthanides & Actinides (f electrons)

PERIODIC TABLE

Divided Into PERIODS (ROWS) And

GROUPS (COLUMNS)

I. METALS

1. REPRESENTATIVE

a) ALKALI ………GROUP IA

b) ALKALINE EARTH……IIA

2. TRANSITION……(B GROUPS)

II. METALLOIDS

III. NONMETALS

WHICH INCLUDE THE HALOGENS AND THE NOBLE GASES.

Selected Properties

of Metals,

Nonmetals and

Metalloids

The Alkali Metals

Reactivity increases as we move

down the group

WHY?

The Alkali Metals

Alkali metals react with water to form

the BASE MOH and hydrogen

gas:

2M(s) + 2H2O(l) → 2MOH(aq) + H2(g)

Alkali metal oxides

4Li(s) + O2(g) → 2Li2O(s) (oxide)

2Na(s) + O2(g) → Na2O2(s) (peroxide)

K(s) + O2(g) → KO2(s) (superoxide)

Alkali metal oxides

Metal oxide + water � metal hydroxide

Na2O(s) + H2O(l) → 2NaOH(aq)

The Alkaline Earth Metals

• The chemistry is dominated by the loss of

two s electrons: M →→→→ M2+ + 2e-.

• Be does not react with water.

• Mg will only react with steam.

• Ca onwards:

Ca(s) + 2H2O(l) →→→→ Ca(OH)2(aq) + H2(g)

Fig 7.14Fig 7.14

Oxygen• Two allotropes:

– O2

– O3, ozone

• Three anions:

– O2−, oxide

– O22−, peroxide

– O21−, superoxide

The Oxygen Group

• As we move down the group the metallic

character increases

• O2 a nonmetal, Te a metalloid, Po a

metal

halogens

All halogens consists of diatomic molecules

Fluorine is one of the most reactive substances known:

2F2(g) + 2H2O(l) → 4HF(aq) + O2(g) ∆H = -758.7 kJ

The Noble Gases

• They are all nonmetals and monatomic.

• They are notoriously unreactive because they have

completely filled s and p sub-shells.

• In 1962 the first compound of the noble gases was

prepared: XeF2, XeF4, and XeF6.

• To date the only other noble gas compounds

known are KrF2 and HArF.

Metals

Metallic character increases down a group.

Metallic character decreases across a period.

Metals have low ionization energies

All group 1A metals form M+ ions.

All group 2A metals form M2+ ions.

Most metal oxides are basic:

Metal oxide + water → metal hydroxide

Na2O(s) + H2O(l) → 2NaOH(aq)

Nonmetals

Most nonmetal oxides are acidic:

nonmetal oxide + water → acid

P4O10(s) + H2O(l) → 4H3PO4(aq)

CO2(g) + H2O(l) → H2CO3(aq)

MetalloidsMetalloids

• Metalloids have properties that are intermediate

between metals and nonmetals.

• Metalloids have found fame in the semiconductor

industry.

End

Chapter 7

Omit Sample & Practice Exercise

7.1 and problems like it

Start with 7.2 : Sizes of atoms

P7.8 Arrange the following atoms in order of

increasing effective nuclear charge

experienced by the electrons in the n = 3

electron shellK Mg P Rh Ti

What information do I need to answer this question ?

P7.18 Using only the periodic table, arrange the following atoms in increasing radius

(a) Cs K Rb

(b) In Te Sn

(c) P Cl Sr

? < ? < ?

? < ? < ?

? < ? < ?

7.24 Select the ions or atoms that are

isoelectronic with each other

(a) K+ Rb+ Ca+2

(b) Cu+ Ca2+ Sc3+

(c) S 2- Se 2- Ar

(d) Fe2+ Co3+ Mn2+

• _____ & _____

• _____ & _____

• _____ & _____

• _____ & ______