1. Lesson 1.5 Covalent bonding
AQA Additional Science
Chemistry 2
Lesson 1.5 Covalent bonding

2. Aims Class work Covalent Bonds LO’s What are covalent bonds?
Write it down!!
Page 45
© C Meyer

3. Aims All Know what a covalent bond is
Know covalent bonds can be either small or large molecules
Most
Draw dot and cross diagrams for covalent bond
Some
Draw dot and cross diagrams for complex molecules

4. Homework
Following the previously shown slides draw bonding diagrams for the compounds formed from the following atoms:
Lithium (2.1) and fluorine (2.7)
Magnesium (2.8.2) and chlorine (2.8.7)
Aluminium (2.8.3) and fluorine (2.7)
Remember that the total number of electrons lost by the metal must equal the total number of electrons gained by the non-metal

5. Copy the diagram and draw another box showing the electron configuration in sodium fluoride.Na
2.8.1.
2.7
Sodium Fluoride
Na+ F- + -
Sodium atom
Fluorineatom
2.8
2.8

7. Bonding in Aluminium Fluoride
In aluminium fluoride it is the non-metal atoms that we need more of. Al F F
Brackets?? Al

8. COVALENT BONDING

9. HCl What are covalent bonds? Hydrogen chloride molecule Info Box
What is different
to ionic bonding?? H 1 Cl Cl 17 H
HCl
Count the electrons in the outer shell of each atom. Are they full?
Click m1

10. Now lets look at a more complicated molecule
Methane
Click

11. Methane (found in natural gas)
Info
Box H 1 C 6 C H
CH4 m1

12. Title - Covalent compounds
What are covalent bonds?
Title - Covalent compounds
Formed when non-metal atoms react together.
Atoms share outer shell electrons.
Shared electrons count towards filling shells of both atoms to make full 2, 8, 8 pattern. m3

13. - What are covalent bonds? F
You need to know different ways to show covalent bonds:-
A pair of electrons shared like this is a covalent bond.
Shown in full bonding diagrams (see figure 1). Or just shown as a pair of electrons (xx) or even just a line (see figure 2). F X -
Figure 1
Figure 2
Ways to show covalent bonds m4

14. Small covalent structures
Can be simple!
Sometimes just a few atoms join together in this way.
This produces small covalent molecules – often known as simple molecular structures.
a simple molecular
structure
covalent bonds

15. Giant covalent structures
Can be complex!!
Sometimes millions of atoms are joined together by covalent bonds.
This produces a rigid 3-D network called a giant lattice.
a giant lattice
covalent bonds

16. Covalent bonding and electron structures
Covalent bonding wants outer electron shells that are completely full.
Done by sharing electrons where shared electrons are in outer shells of both atoms.
Can be done with more than 2 atoms C H N H Cl H Cl

17. Covalent bonding in chlorine
Chlorine (2.8.7) needs 1 more electron to attain a full electron shell.
Draw it!
Cl-Cl Cl
(2,8,7) Cl
(2,8,7) Cl
(2,8,8) Cl
(2,8,8)

18. Covalent bonding in hydrogen chloride
Both hydrogen (1) and chlorine (2.8.7) needs 1 more electron to attain a full outer shell. Another example
Electronic structure of H and Cl?? Cl
(2,8,7) H
(1)
H-Cl Cl
(2,8,8) H
(2)
Electronic structure of HCl?? m2

19. Covalent bonding in water
What are we going to do with water??
Hydrogen (1) needs 1 more electron but oxygen (2.6) needs 2 more.
Electronic structure of H and O?? O H O H O H

20. Hydrogen (1) needs 1 more electron.
How many does nitrogen (2.5) need? 3
How many hydrogens per 1 nitrogen? 3
Draw bonding diagrams for ammonia. N H N H

21. How could we draw this with lines?
Hydrogen (1) needs 1 more electron.
How many does carbon (2.4) need to make 8? 4
How many hydrogens per 1 carbon? 4
Draw bonding diagrams for methane. C H C H
How could we draw this with lines?

22. Covalent bonding - multiple bonds
Mostly electrons are shared as pairs.
In some compounds they are shared in fours or even sixes.
This gives rise to double and triple covalent bonds.
Again, each pair of electrons is often represented by a single line when doing simple diagrams of molecules.
Cl-Cl
Single bond
O=O
Double bond
N=N
Triple bond

23. Covalent bonding in oxygen
Oxygen (2.8.6) needs 2 more electrons to attain a full electron shell. O
O=O
4 electrons O

24. Nitrogen (2.8.5) needs 3 more electrons to attain a full electron shell and forms a triple bond.
Draw a bonding diagram of nitrogen. N
6 electrons
N=N N

25. Giant covalent structures: diamond
strong
covalent
bonds
carbon atoms
One form of carbon is diamond.
Each diamond consists of millions of carbon atoms bonded into a single giant structure.
It is very hard.

26. Giant covalent structures: sand
Sand is an impure form of silicon dioxide.
Although it is a compound, it has a giant covalent structure with certain similarities to diamond.
silicon atoms
oxygen atoms

27. What have I learnt? Ionic or covalent bonds?? Methane Sodium Chloride
Oxygen
Water
Magnesium Oxide
Carbon
Calcium Chloride
Explain covalent bonding

28. What have I learnt?

29. The End