1. Chapter 6
Chemical Bonding

2. contents You will learn about: Ionic bonds – electron transfer
Covalent bonds – electron sharing
Properties of ionic and covalent compounds

3. The noble gases
(Group 0 elements) are also known as inert gases. They are gases.

4. Noble Gas Electronic Configuration
When the outer shell of an element is completely filled with electrons, the element is very stable.
Atoms of noble gases in Group 0 are very stable. Hence, they do not react with other elements.
Noble gas configurations are very stable because they have fully filled outer/valence shells.

5. Noble gases (except for helium) have 8 electrons in their outer shells.
Examples
Arrangement of electrons in the outer shell He
helium 2
Duplet structure Ne
neon
Octet structure
2.8 Ar
argon
Octet structure
2.8.8

6. The tendency for atoms to surround themselves with a stable ‘octet’ of electrons is called the octet rule.
Helium has only 2 electrons in its outer shell , but is stable as it too has a fully filled outer shell of electrons.
The maximum number of electrons that can be accommodated in the 1st shell is 2. This is called the duplet rule.

7. Other elements do not have the stable electronic configuration where the outer shell is fully filled with electrons forming either the duplet or octet structure.
Thus, they react with one another by losing, gaining or sharing their valency electrons to achieve the stable noble gas electronic configuration during a chemical reaction.
( valency electrons are electrons in the outer shell used in chemical bonding)

8. Chemical bonding Covalent bonding Ionic bonding
By losing or gaining of electrons (i.e transferring of electrons)
Takes place between atoms of metals and non-metals
By sharing of electrons between atoms of non-metals
Covalent substances
Ionic compounds

9. -  + Formation of Cations (positive ions) and Anions (negative ions)
An ion is a charged particle formed from an atom or a group of atoms by the loss or gain of electrons .It can be either positively or negatively charged.
atoms form ions by gaining or losing electrons to obtain the stable electronic structure of a noble gas -
negative ion 
add electrons
more electrons than protons
neutral atom
electrons = protons +
remove electrons
positive ion
more protons than electrons

10. Electronic configuration of Metals & Non-metals

11. Electronic configuration of Metals & Non-metals
Metals tend to lose their valence electrons to achieve the stable noble gas electronic configuration as they have few valence electrons.
Non-metals tend to gain electrons to achieve the stable noble gas electronic configuration as they have a lot of electrons in their valence shell
Note : only the valence (outer) electrons are involved in bonding; those in the complete inner shells do not take part.

12. Li atom loses an electron readily and become a lithium ion, Li+
Formation of Cations
Examples
Li atom loses an electron readily and become a lithium ion, Li+

13. + loses 1 electron 2,8 Na+ ion Na atom 2,8,1 11 protons 11 protons
Na atom loses an electron and becomes a positive ion, sodium ion, Na+ which have the stable noble gas electronic structure as Neon (2,8).
loses 1 electron + Na
2,8
Na+ ion
Na atom
2,8,1
11 protons
10 electrons
12 neutrons
11 protons
11 electrons
12 neutrons
Charged (+1)
Neutral
11 protons (+11) and
10 electrons (-10)
 overall charge = ( ) = +1
[all +ve charges (protons) balanced by -ve charges (electrons)]

14. 3+ loses 3 electrons 2,8 Al3+ ion Al atom 2,8,3 13 protons 13 protons
Al atom loses 3 electrons and becomes a positive ion, aluminium ion, Al3+ which have the stable noble gas electronic structure as Neon (2,8). 3+
loses 3 electrons Al Al
2,8
Al3+ ion
Al atom
2,8,3
13 protons
10 electrons
14 neutrons
13 protons
13 electrons
14 neutrons
Charged (+3)
Neutral
13 protons (+13) and
10 electrons (-10)
 overall charge = ( ) = +3
[all +ve charges (protons) balanced by -ve charges (electrons)]

15.  Now You Try! Draw diagrams to show the formation of
(a) A potassium ion
(b) A calcium ion

16. Formation of Anions ¯ gains 1 electron
Cl atom gains 1 electron from a metal atom and becomes a negative ion, named as chloride ion, Cl- which has the same noble gas electronic structure as Argon (2,8,8). x Cl
gains 1 electron Cl
chlorine atom
2,8,7
chloride ion
2,8,8
17 protons
17 electrons
18 neutrons
Charged (-1)
17 protons (+17) and
18 electrons (-18)
 overall charge = ( ) = -1
17 protons
18 electrons
18 neutrons
Neutral

17. Now You Try ……… Draw diagrams to show the formation of
a fluoride ion (b) an oxide ion (c) a nitride ion

18. Cations- more examples12 10 19 18
Number of electrons 20
No of protons Mg
Mg2+ K K+
Symbol
Magnesium atom
Magnesiumion
Potassium
atom
Number of neutrons 24 39
Note: A positive ion still has the same number of protons
and neutrons as its atom, but, it will have less
electrons than protons.

19. Anions – more examples
Sulphur
atom
Sulphide ion
Oxygen atom
Oxide ion
Symbol S 32
S2- 32 O 16
O2- 16 16 16 8 8 8 16
No of protons
Number of electrons 16 18 8 10 16 8
Number of neutrons
Note: A negative ion still has the same number of
protons and neutrons as its atom, but, it will
have more electrons than protons.

20. Ionic bonding – involves the transfer of electrons from one atom to another so that each can achieve the noble gas electronic configuration.
usually formed between atoms of metals and non-metals
positive and negative ions are formed after the transfer of electrons
The oppositely charged ions are attracted to each other by strong electrostatic force of attraction.

21. This strong electrostatic force of attraction between the oppositely charged ions is called ionic bond.
Example

22. ionic bonds – electron transfer

24. Diagrammatic Representation of Ionic Bonding
Example 1 Formation of sodium chloride through ionic bonding
chlorine atom, Cl
2.8.7
electron transfer
sodium atom, Na
2.8.1

25. - 2.8 2.8.8 An ionic compound, sodium chloride ( NaCl ) is formed. +
- electron
of Na
- electron
of Cl Na Cl
sodium ion, Na+
2.8
chlorine ion, Cl-
2.8.8
has the same electronic structure as the noble gas, neon
has the same electronic structure as the noble gas, argon
‘DOT and CROSS’ Diagram

26. ionic bonds – electron transfer
Example Formation of magnesium chloride
through ionic bonding
electron transfer
electron transfer Mg Cl Cl
magnesium atom, Mg
2.8.2
chlorine atom, Cl
2.8.7
chlorine atom, Cl
2.8.7

27. ionic bonds – electron transfer
has the same electronic structure as the noble gas, neon
has the same electronic structure as the noble gas, argon
magnesium ion, Mg2+
2.8 2+
chloride ion, Cl-
2.8.8 - Cl Mg

28. Compounds with ionic bonds
Ionic bonds are formed between atoms of metals and non-metals in compounds.
Examples include:
Compounds with ionic bonds
Elements
Name
Formula
Metals
Non-metals
sodium chloride
NaCl
sodium
chlorine
magnesium oxide
MgO
magnesium
oxygen
potassium iodide KI
potassium
iodine
calcium bromide
CaBr2
calcium
bromine

29. Structures of Ionic Compounds
Ionic compounds have giant ionic lattice structure.

30. Properties of ionic compounds
I. Boiling points and Melting Points
Have high melting points (above 250oC) and high boiling points (above 500oC)
Reason: The ionic bonds (electrostatic force of attraction) between the ions are very strong . A very large amount of heat energy is needed to overcome these strong bonds.
This also explains why all ionic
compounds are solids at
room temperature. + -

31. II. Solubility
Ionic compounds are usually soluble in water but insoluble in organic solvents.
Reason: water molecules can separate the positive ions from the negative ions, causing them to dissolve.
Exceptions: silver chloride, barium sulphate are ionic compounds which are insoluble in water.
Organic solvents eg petrol, alcohol and turpentine

32. properties of ionic compounds
III Electrical conductivity
Ionic compounds do not conduct electricity in the solid state because the ions are not free to move about.
When the substance is in molten state (melted in liquid form)) or aqueous state ( when dissolved in water), it can conduct electricity.
Reason : In these states, the ions are free to move. The moving ions conduct electricity.

33. What is covalent bond?
Covalent bond is a bond formed by the sharing of electrons between atoms of non-metals.
After bonding, each atom attains the stable noble gas electronic configuration.
Why must atoms of non-metals share electrons while atoms of metals and non-metals form ions?

34. Why covalent bonds are formed between non-metal atoms?
For elements with 4 valency electrons, gaining or losing 4 electrons to achieve a noble gas electronic configuration requires a large amount of energy. Thus, the non-metallic elements combined by sharing of electrons to form molecules.
Valency electrons - are electrons in the outermost
shell used to form bonds.
Valency - is the number of electrons an atom uses to
form bonds
Valence electrons - are electrons in the outermost shell

36. The molecules formed can be
Simple covalent molecules like H2, O2, H2O, CO2, NH3, CH4, HCl, N2, Cl2, etc or
(ii)Giant covalent molecules (or macromolecules)( which is a three dimensional network of atoms bonded together by covalent bonds to form a giant molecule ) like diamond, graphite, silicon dioxide, etc

37. Electronic Structure of Molecule (‘Dot and Cross’ Diagram)
Formation of Covalent Bonds
Covalent Molecule
Chemical formula
Electronic Structure of Molecule (‘Dot and Cross’ Diagram)
Structural diagram
hydrogen gas H2
Other ways to represent :
H H H
Single covalent bond H + H
H atom
H atom H H x o
H2 molecule

38. Other ways to rep : H or H O xx x O H H Covalent Molecule Formula
Electronic Structure of Molecule (‘Dot and Cross’ Diagram)
Simple Way of Showing the Bonds
water
H2O O H H H O
Other ways to rep : or
H O xx x H H

39. C or H H H H x x x x H C Other ways to rep : Covalent Molecule Formula
Electronic Structure of Molecule (‘Dot and Cross’ Diagram)
Simple Way of Showing the Bonds
methane
CH4 H C H H C H H
Other ways to rep : or H x x H C x H x H

40. Other ways to rep : x xo ox x or x O xoC ox O x xx xx O C
Covalent Molecule
Formula
Electronic Structure of Molecule (‘Dot and Cross’ Diagram)
Simple Way of Showing the Bonds
carbon dioxide
CO2 O C O C
Other ways to rep :
x xo ox x
or x O xoC ox O x
xx xx

41. Electronic Structure of Molecule (‘Dot and Cross’ Diagram)
Covalent Molecule
Formula
Electronic Structure of Molecule (‘Dot and Cross’ Diagram)
Structural diagram
oxygen O2 O O O O
Double bond
(2 pairs of electrons)
Other ways to rep :
x x o o
or xo
O xo O

42. Electronic Structure of Molecule (‘Dot and Cross’ Diagram)
Covalent Molecule
Formula
Electronic Structure of Molecule (‘Dot and Cross’ Diagram)
Structural diagram
nitrogen N2 N N N N
Triplebond
(3 pairs of electrons)
Other ways to rep :
x x o o
or xo
N xo N xo

43. Structure of Covalent Substances
(a) Simple Molecular Structure
Example 1 :Iodine is a simple diatomic covalent molecule.
It has a simple molecular structure.
Reason : There exists weak intermolecular forces of attraction, between the iodine molecules, also known as weak Van der Waals’ forces. These weak forces of attraction requires only a small amount of heat enerrgy to overcome.

44. Example 2 Methane is also a simple covalent molecule.
Four covalent bonds (C-H) are held together by strong forces of attraction. However, weak Van der Waals’ forces between methane molecules hold them together loosely. Therefore, methane exists as a gas at room temperature and pressure.

45. Properties of simple covalent compounds
volatility
Covalent molecules have strong covalent bonds between atoms, but the Van der Waals’ forces which exist between separate molecules are weak.
During melting or boiling, the molecules do not break up into atoms, but merely move further apart.
Thus, simple covalent molecules are volatile, i.e., they have low melting points and boiling points, as not much heat energy is needed to overcome the Van der Waals’ forces.
Molecules do not break up into atoms but merely move further apart during melting and boiling

46. Properties of simple covalent compounds
solubility
Most covalent molecules are insoluble in water but are usually soluble in organic solvents.
Exceptions: Alcohol and sugar are covalent compounds which are soluble in water.
Some covalent molecules dissolve in water because of chemical reactions. E.g., chlorine.
electrical conductivity
Covalent substances (elements or compounds) do not conduct electricity whether in the solid or molten state. This is because they do not contain ions or free electrons.
Exceptions: carbon, in the form of graphite, conducts electricity. Covalent compounds such as hydrogen chloride and hydrogen sulphide also conduct electricity when dissolved in water.

47. Differences between Ionic and Covalent Bonding
Ionic Bond
Covalent Bond
Formed between metals and non-metals.
Formed by transferring of electrons.
Formed between non-metals and non-metals.
Formed by sharing of electrons.

48. properties of ionic and covalent compounds
summary of main differences in properties between ionic compounds and covalent compounds
Property
Ionic Compounds
Covalent Compounds (with simple Molecular Structure)
Boiling point
high
low
Electrical conductivity
do not conduct electricity when solid; conduct when molten or dissolved in water
do not conduct electricity in any form
Solubility in Water
usually soluble
usually insoluble
Solubility in organic solvents
insoluble
soluble

49. properties of ionic and covalent compounds