1. Leaving Certificate Chemistry
5 – Covalent Bonding
Leaving Certificate Chemistry

2. Objectives for today To learn what a covalent bond is
To draw what happens in bonds using Bohr diagrams and dot and cross diagrams

3. Covalent Bonding

4. Formation of Chlorine (Cl2)
Formed from 2 chlorine sharing a pair of electrons with each chlorine contributing 1 electron to the covalent bond
Outer Shell Cl Cl Cl Cl
One Shared Pair of Electrons = A single bond

5. N N N N O H H O H H Dot & Cross Diagrams X X X X X X X
For a Nitrogen Molecule (N2) X N N N N X X X X
For a Water Molecule (H2O) O H H O X X H H

6. Double Covalent Bonds
For ethene (C2H4)

7. Triple Covalent Bonds
For ethyne (C2H2)

8. Learning objectives Today you should learn about..
What a polar covalent bond is
Two examples of a polar compounds
The dissolving rule

9. Investigating the characteristics of covalent compounds
Test
Circle the correct characteristic
Try to break the substance
It is brittle/ it is soft and squashy/ it is very strong
Try to dissolve the substance in water
It is soluble in water / it is not soluble in water
Try to heat the substance – what happens
It has low melting and boiling points/ it has high melting and boiling points
Try to pass electricity through the substance
It does not conduct electricity/ it does conduct electricity when molten or in solution

10. The Characteristics of Covalent Compounds
They have low melting points and low boiling points
They do not conduct electricity
They are usually insoluble in water 10

11. Melting and boiling point: molecules
Simple molecular substances have low melting and boiling points because the molecules together are not held tightly together.
weak bonds between molecules
strong bonds within molecules

12. Conductivity – covalent substances
Substances with covalent bonding do not conduct electricity because there are free electrons to carry a charge through a solution
electrons unable to move and carry a charge

13. Polar Covalent Bonds

14. H F Polar Covalent Bonds X
Hydrogen Fluoride is an example of a polar covalent molecule
δ - δ+ H F X

15. O H H Polar Covalent Bonds X X
Water is another example of a polar covalent molecule
δ 2- O X X δ+ H H δ+

16. Testing if a liquid is polar
If a liquid is polar covalent then it will be deflected towards a charged rod.
Try out this test with some liquids and see which are polar!!!

17. Demonstration The Polarity Test for Liquids Charged Rod
Non polar – hexane, cyclohexane
Charged Rod
A polar covalent compound will deflect towards a charged rod

18. Polar Substances in Everyday Life
Alcohol (Ethanol)
Water

19. Non-Polar Substances in Everyday Life
Toluene (Methylbenzene) is a common industrial solvent
Acetone in nail varnish remover

20. Investigating which dissolves which
Name of substance
Is it ionic, polar covalent or pure covalent
Name of solvent
Is it pure covalent or polar covalent/
Did it dissolve?
Sodium chloride
ionic
Water
Polar covalent
Toluene
Pure covalent
Iodine
Pure covelent

21. Solubility of different substances
In general …Like Dissolves Like
Ionic substances and polar covalent substances will dissolve in polar covalent solvents.
Pure Covalent substances will dissolve in nonpolar solvents
water, cyclohexane, ethanol, and glycerol.
Candle wax