IB Chemistry Bonding Topic 4

1. LECTURE 1
Ionic Bonding
IB Chemistry Power Points
Topic 4
Bonding
www.pedagogics.ca

3. STRUCTURE AND BONDING

4. TYPES OF BONDING
CHEMICAL BONDS....
are strong intramolecular bonds that hold atoms
together in molecules, ionic solids and metals. These
bonds are broken and made in chemical reactions.
ionic
covalent
dative covalent (or co-ordinate)
metallic
PHYSICAL BONDS....
are intermolecular forces that exist between two or
more separate molecules. These are the attractions
involved in physical changes.
van der Waals‘ forces - weakest
dipole-dipole interactions
hydrogen bonds - strongest

5. PART 1: CHEMICAL BONDS

6. THE IONIC BOND
Ionic bonds are formed between elements whose atoms tend to “lose”
electrons to gain the nearest noble gas electron configuration and those which
tend to “gain” electrons. The electrons are transferred from one atom to the
other.
Sodium Chloride
Na ——> Na
+
+ e¯ and Cl + e¯ ——> Cl¯

7. THE IONIC BOND
Ionic bonds are formed between elements whose atoms tend to “lose”
electrons to gain the nearest noble gas electron configuration and those which
tend to “gain” electrons. The electrons are transferred from one atom to the
other.
Sodium Chloride
Na ——> Na
+
+ e¯ and Cl + e¯ ——> Cl¯
oxidation reduction

8. THE IONIC BOND
Ionic bonds are formed between elements whose atoms tend to “lose”
electrons to gain the nearest noble gas electron configuration and those which
tend to “gain” electrons. The electrons are transferred from one atom to the
other.
Sodium Chloride
Na ——> Na
+
+ e¯ and Cl + e¯ ——> Cl¯
oxidation reduction
2,8,1 2,8 2,8,7 2,8,8

9. THE IONIC BOND
Ionic bonds are formed between elements whose atoms tend to “lose”
electrons to gain the nearest noble gas electron configuration and those which
tend to “gain” electrons. The electrons are transferred from one atom to the
other.
Sodium Chloride
Na ——> Na
+
+ e¯ and Cl + e¯ ——> Cl¯
oxidation reduction
2,8,1 2,8 2,8,7 2,8,8
1s
2
2s
2
2p
6
3s
1
1s
2
2s
2
2p
6
1s
2
2s
2
2p
6
3s
2
3p
5
1s
2
2s
2
2p
6
3s
2
3p
6

10. SODIUM CHLORIDE – LIVE BOND FORMATION
Cl
SODIUM ATOM
2,8,1
Na
CHLORINE ATOM
2,8,7

11. SODIUM ION
2,8
CHLORIDE ION
2,8,8
both species now have ‘full’ outer shells; ie they have the
electronic configuration of a noble gas
Oppositely charged ions are held together by electrostatic forces
in a repeating pattern called a crystal lattice structure
Na
+
Cl

12. ELECTRON
TRANSFER
Mg ——> Mg
2+
+ 2e¯ and 2Cl + 2e¯ ——> 2 Cl¯
Mg
Cl
Cl
e¯
e¯
FORMATION OF MAGNESIUM CHLORIDE

13. MAGNESIUM CHLORIDE - LIVE
Cl
MAGNESIUM ATOM
2,8,2
Mg CHLORINE ATOMS
2,8,7
Cl

14. Cl
MAGNESIUM ION
2,8
Mg CHLORIDE IONS
2,8,8
Cl
2+

15. • also known as cations; they are smaller than the original atom.
• formed when electrons are removed from atoms.
• the energy associated with the process is known as the ionisation energy
Recall: 1st IONISATION ENERGY (1
st
I.E.)
The energy required to remove one mole of electrons (to infinity) from the one
mole of gaseous atoms to form one mole of gaseous positive ions.
e.g. Na(g) ——> Na
+
(g) + e¯ or Mg(g) ——> Mg
+
(g) + e¯
Other points (HL topic 12)
Successive IE’s (2
nd
, 3
rd
, etc) get larger as the proton:electron ratio increases.
Large jumps in value occur when electrons are removed from shells nearer the
nucleus because there is less shielding and more energy is required to
overcome the attraction.
If the I.E. values are very high, covalent bonding will be favoured (e.g.
beryllium).
THE FORMATION OF POSITIVE IONS - review

16. • known as anions
• are slightly larger than the neutral atom - electron repulsion in outer shell
• formed when electrons are added to atoms
• energy is released as the nucleus pulls in an electron
• this energy is the electron affinity.
ELECTRON AFFINITY
The energy change when one mole of gaseous atoms acquires one mole of
electrons (from infinity) to form one mole of gaseous negative ion
e.g. Cl(g) + e¯ ——> Cl¯(g) and O(g) + e¯ ——> O¯(g)
The greater the effective nuclear charge (E.N.C.)of a species, the easier an
electron is attracted.
THE FORMATION OF NEGATIVE IONS - review

17. Octet Rule - Ions form from a tendency toward a
lower energy, stable, noble gas electron
configuration
Transition metals have more complex electron arrangements
thus can form more than one ion.

18. IONIC COMPOUNDS - CRYSTAL LATTICE STRUCTURE
Cl-
Chloride ion
Na
+
Sodium ion
Oppositely charged ions held in a regular
3-dimensional lattice by electrostatic attraction
The arrangement of ions in a crystal lattice depends on the relative sizes of the ions
The Na
+
ion is small enough relative to a Cl¯ ion to fit in the
spaces so that both ions occur in every plane.

19. Each Na
+
is surrounded by 6 Cl¯
and each Cl¯ is surrounded by 6 Na
+
Oppositely charged ions held in a regular 3-dimensional
lattice by electrostatic attraction:
The arrangement of ions in a crystal lattice depends on the relative sizes
of the ions

20. Physical properties of ionic compounds
Melting point
very high A large amount of energy must be put in to overcome the
strong electrostatic attractions and separate the ions.
Strength
Very brittle Any dislocation leads to the layers moving and similar
ions being adjacent. The repulsion splits the crystal.
Electrical don’t conduct when solid - ions held strongly in the lattice
conduct when molten or in aqueous solution - the ions
become mobile and conduction takes place.
Solubility Insoluble in non-polar solvents but soluble in water
Water is a polar solvent and stabilises the separated ions.

21. IONIC COMPOUNDS - ELECTRICAL
PROPERTIES
SOLID IONIC
COMPOUNDS DO
NOT CONDUCT
ELECTRICITY
Na
+
Cl
-
Na
+
Cl
-
Na
+
Cl
-
Na
+
Cl
-
Na
+
Cl
-
Na
+
Cl
-
IONS ARE HELD STRONGLY TOGETHER
+ IONS CAN’T MOVE
- IONS CAN’T MOVE
MOLTEN IONIC
COMPOUNDS DO
CONDUCT
ELECTRICITY
Na
+ Cl
-
Na
+
Cl
-
Na
+
Cl
-
Na
+
Cl
-
IONS HAVE MORE FREEDOM IN A
LIQUID SO CAN MOVE TO THE
ELECTRODES
SOLUTIONS OF IONIC
COMPOUNDS IN
WATER DO CONDUCT
ELECTRICITY
DISSOLVING AN IONIC COMPOUND
IN WATER BREAKS UP THE
STRUCTURE SO IONS ARE FREE TO
MOVE TO THE ELECTRODES

22. Many ionic compounds are soluble in water - dissolving