1. Covalent bonding

2. Group IV atoms
Group IV atoms do not lose or gain electrons in order to obtain the octet structure.
They prefer to share electrons with other atoms to form molecules.
The electrostatic attraction force between shared electrons and positive nuclei is called covalent bond.

3. Molecules C H x
Methane CH4
Tetrachloromethane, CCl4 C Cl x

4. Molecules Si H x
Silane SiH4
Silicon tetrachloride, SiCl4 Si Cl x

5. Molecules Hydrogen H2 Chlorine, Cl2 Fluorine, F2 Single bond H+ x H
Bond pair
Hydrogen H2
Chlorine, Cl2
Fluorine, F2 x x x x x x Cl x + Cl x Cl Cl x x x x x x
Single bond + x F

6. Molecules Oxygen, O2 Nitrogen N2 Hydrogen chloride, HCl Double bond+ x O
Oxygen, O2
Nitrogen N2
Hydrogen chloride, HCl
Double bond + x N
Triple bond + x H Cl

7. Molecules Ammonia NH3 Phosphorus trichloride, PCl3 Lone pair H N P Clx
Lone pair
Ammonia NH3
Phosphorus trichloride, PCl3 P x Cl

8. Molecules H O x
Lone pair
Water, H2O
Carbon dioxide CO2 x O C

9. Molecular formulae

10. Molecular formulae

11. Molecules Molecules are formed from non-metal elements.
There are strong covalent bonds within molecules.
However, only weak van der Waals’ forces between molecules.

12. Simple molecular structure
Water, ammonia, dry ice (solid carbon dioxide)
o = c = o
Weak van der Waals’ forces

13. Simple molecular structure
Iodine
Iodine molecule

14. Properties of simple molecular compounds
They are usually liquids (water) and gases (oxygen).
Only a few is solids (iodine and dry ice).
The solids are relatively soft.
Low melting points and boiling points.
Usually they are insoluble in water, but soluble in 1,1,1-trichloroethane.
They are electrical non-conductors (without mobile ions).

15. Reasons
They have simple molecular structures with weak van der Waals’ forces between molecules.

16. Carbon atom
Carbon atom do not lose or gain electrons in order to obtain the octet structure.
It prefers to share electrons with other atoms to form molecules.
How about in pure carbon? How do carbon atoms combine together?

17. Carbon atom
Each carbon atom has 4 outermost shell electrons, they tend to gain 4 extra electrons to obtain octet structure. As a result, each carbon atom forms covalent bonds with 4 other carbon atoms. C x C x
extend infinitely

18. Diamond
Diamond has a giant covalent structure with of a network of strong covalent bonds.
Each carbon atom is covalently bonded to 4 other carbon atoms.
Similar for silicon.
Carbon atoms
Covalent bonds

19. Graphite
Graphite is another form of carbon. It has very high melting point and boiling point. It conducts electricity and so it is used as electrode.

20. silicon
oxygen
Quartz, SiO2
Silicon and carbon are group IV elements, so they are similar in structure.
When silicon combine with oxygen, each silicon atom is covalently bonded to 4 oxygen atoms.
While each oxygen atom is covalently bonded to 2 silicon atoms.
Therefore, the formula is SiO2.

21. Giant covalent structure
Diamond and quartz are both giant covalent compounds.
Their melting points (diamond: ~3500C) and boiling points are very high.
They are very hard and insoluble in water.
They are electrical insulator (except graphite).
They have giant covalent structure with a network of strong covalent bonds between atoms.