1. Chemical bonding
Covalent Bonding

2. Bonding and structure explains the properties of a substance!
Overview
Bonding
Ionic
Covalent
Metallic
Structure
Giant ionic
Simple molecular
Giant covalent
Giant Metallic
Example
Sodium chloride
Water
Diamond
Iron
Bonding and structure explains the properties of a substance!

3. Structure of Covalent Substances
Covalent substances may exist as:
simple molecular structures
giant covalent structures
Diamond
Graphite
Silicon dioxide

4. ‘Allotropes’: Different (structural) forms of the same element
Diamond
One of the allotropes of carbon
Diamond is one form of the element carbon.
‘Allotropes’: Different (structural) forms of the same element
‘Isotopes’: Atoms of the same element with the same number of protons but different number of neutrons

5. These four carbon atoms form a tetrahedron.
Diamond
Has a giant covalent structure
Giant network of carbon atoms held together by covalent bonds in a tetrahedral arrangement
These four carbon atoms form a tetrahedron.

6. Diamond
Each carbon is joined to four other carbon atoms by strong covalent bonds.
Each carbon has four
covalent bonds.

7. Properties of Diamond Very high M.P. and B.P.
(Diamond melts at about 3500°C)
Hardest natural substance
Reason:
Carbon atoms are held together in a giant rigid structure by strong covalent bonds.
A lot of energy is required to break these strong covalent bonds.

8. Properties of Diamond Does not conduct electricity Insoluble in water
All electrons are held in the covalent bonds.
No ions or free electrons to conduct electricity
Insoluble in water

9. Uses of Diamond
Used in cutting other hard solids (because of its hardness)
E.g. Diamond-tipped drills to cut through rock

10. Graphite Another form of the element carbon
Another allotrope of carbon
Has a giant covalent structure
Consists of layers of carbon atoms
(flat two-dimensional layers)

11. Graphite Within the layer
Each carbon atom is joined to three other carbon atoms by strong covalent bonds.
Arranged in rings of six atoms

12. Arrangement of carbon atoms in one layer
Structure of Graphite
Arrangement of layers
Arrangement of carbon atoms in one layer
Strong covalent bond
Strong covalent bond
Weak force between layers

13. Properties of Graphite
Very high M.P. and B.P.
(Within each layer) The bonds between the carbon atoms are difficult to break – strong covalent bonds
Soft and slippery
Weak forces between the layers
 the layers can slide past each other
Strong covalent bond
Weak force between layers

14. Properties of Graphite
The only non-metal that conducts electricity
Reason:
Each carbon atom has one valence electron that is not used in bonding.
Free to move  Able to conduct electricity

15. Uses of Graphite Pencil lead: Made of graphite and clay
Since it is soft, it flakes off and stick to paper when we write.
Lubricant (for hot machines)
It does not decompose at high temperatures.

16. Silicon Dioxide a.k.a. silica Found in nature as sand or quartz
Consists of silicon and oxygen atoms
Has a giant covalent structure like diamond
SiO2 tells us the ratio of silicon atoms to oxygen atoms is 1:2

17. Physical Properties of Giant Covalent Substances
Physical state
At room temperature, all substances with a giant covalent structure are solids.
Strong covalent bonds make it hard.
M.P. and B.P.
High M.P. and B.P. because of its strong covalent bonds

18. Physical Properties of Giant Covalent Substances
Solubility in water
Insoluble in water
Electrical conductivity
Do not conduct electricity (except graphite!)
Diamond
Graphite

19. Chemistry Insights TB Practice Questions Chapter 6 (P.110-113)
MARCH HOLIDAYS HW