1. S2 Chemistry
Covalent Bonding

2. Word Equations Learning Intention
We are learning about covalent bonding

3. Success Criteria
I can describe a covalent bond in terms of atoms sharing electrons
I can explain how a covalent bond holds two atoms together.
I can explain what is meant by a discrete molecule
I can explain what is meant by a covalent network substance
I can state that covalent bonds within a molecule are strong and that the forces of attraction between molecules are weak

4. The Covalent Bond
The covalent bond is a shared pair of electrons between non metal atoms.
H2 gas - + - +

5. The Covalent Bond
The two atom are held together by the electrostatic attraction of the protons to the shared pair of electrons.

6. The Covalent Bond
A molecule is 2 or more atoms joined by covalent bonds

7. The Covalent Bond
The atoms share electrons so that they achieve the stable arrangement of the noble gasses.

8. The Covalent Bond
The first electron energy level can only hold 2 electrons then it is full.
Hydrogen achieves this stable arrangement by sharing an electron with another atom

9. The Covalent Bond
When 2 fluorine atoms come close enough they overlap their electron clouds to share a pair of electrons x x o o x x o x F o F o x x o o

10. The Covalent Bond
When 2 fluorine atoms come close enough they overlap their electron clouds to share a pair of electrons x x o o x x F F o o x o x x o o F F

11. The Covalent Bond
Each atom would now appear to have the same electron arrangement as the noble gas neon.
We can write the fluorine molecule as
F-F or F2

12. The Covalent Bond
Oxygen x x o x o o x o o x x o

13. The Covalent Bond
Oxygen x o o x o x x x o o x o

14. The Covalent Bond
Oxygen x o o x o x x o x o x o
The oxygen molecule has two shared pairs of electrons
It can be written as O O of O2

15. Conduction
Covalent compounds never conduct electricity.
Demo

16. Molecular Models Black = carbon White = hydrogen Red = oxygen
Green = fluorine/chlorine/iodine
Blue = nitrogen

17. Molecular Models
It is very difficult to draw molecular models so chemists use a short version.

18. Molecular Models Use the molecular models to make up a model of –
Fluorine
Oxygen
nitrogen

19. Molecules
Molecules are described as discrete.

20. Molecules Molecules are described as discrete.
This means that each molecule is separate from the next.

21. Molecules Molecules are described as discrete.
This means that each molecule is separate from the next.
Between the molecule there is very little holding them together

22. Molecules Molecules are described as discrete.
This means that each molecule is separate from the next.
Between the molecule there is very little holding them together
Within the molecules they are held together by strong covalent bonds.

23. Molecular Explanations
H O H O
Strong covalent bond
Within molecules H H
Weak attraction between molecules

24. Electron Clouds
The electrons in an atom are not actually arranged in the structured form shown in the target diagram.

25. Electron Clouds
The electrons in an atom are not actually arranged in the structured form shown in the target diagram. x x x x x x x F x x

26. Electron Clouds
The first level is spherical in shape while the second and third are tetrahedral. x x x x x x x F x x

27. Electron Clouds
The first level is spherical in shape while the second and third are tetrahedral. x x x x x x x F x x

28. Electron Clouds
The electrons fill each of the ‘petals’ singly at first and then they pair up. x x x x x x x x x F x x x x x x x

29. Electron Clouds
The electrons fill each of the ‘petals’ singly at first and then they pair up.
Single electrons x x x x x x x x x F x x x x x x x

30. Electron Clouds
The tetrahedral shape of the clouds give an indication of the shape of the molecules.

31. Eg methane

32. Covalent Network Structures
A covalent network structure is a vast 3-dimensional arrangement of atoms strongly bonded together by covalent bonds.

33. Covalent Network Structures
Unlike molecules which have a definite formula, there is no fixed number of atoms in a covalent network.

34. Covalent Network Structures
Each line in the diagram represents a covalent bond – a shared pair of electrons. In this way each carbon atom achieves the stable octet of electrons.
The diamond structure can be described as a lattice because of its regular repeating pattern.

35. Covalent Network Structures
There are only carbon atoms in diamond so the formula is just C.
The formula for silicon dioxide, SiO2 indicates that the proportion of silicon atoms to oxygen atoms is 1:2

36. Covalent Network Properties
Properties of silica
Result
appearance
solubility
melting
conduction
hardness

37. Covalent Network Properties
Properties of silica
Result
appearance
transparent solid
solubility
Not soluble in water
melting
1713°C
conduction no
hardness
Very hard

38. Covalent Network Properties
Compared to molecular substances, covalent networks are very hard and have a very high melting point.
Compared to ionic substances, covalent networks are not soluble in water and do not conduct when liquid (no charged particles).

39. Covalent Network Properties
Covalent network substances are very hard solids because the strong covalent bonds extend throughout the structure
To melt these substances the strong covalent bonds must be broken and this takes a considerable amount of energy.

40. Bonding Learning Intention
We are learning about the 4 different types of bonding

41. Bonding Success Criteria I can describe the 4 types of bonding
I can describe the properties of the different types of compounds
I can give examples