1. Chemical 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. Physical & Chemical Properties
‘property’: ‘what something is like’
Physical properties of a substance are those that can be observed or measured without the substance changing into another substance.
Chemical properties of a substance describe the change of a substance into another substance.
Some examples of physical properties:
Solubility in water (or other solvents)
Melting and boiling points
Electrical conductivity

4. Ionic Bond: The Definition
An ionic bond…
is the force of attraction between opppositely charged ions in a compound.

5. Giant Ionic Structures Physical Properties: M.P. & B.P.
Ionic compounds have high melting and boiling points.
strong electrostatic forces of attraction between the ions in an ionic compound
large amount of heat is needed to break the strong ionic bonds holding the ions together

6. Giant Ionic Structures Physical Properties: Electrical Conductivity
Ionic compounds do not conduct electricity in the solid state. It conducts electricity in the molten and aqueous state.
Why do ionic compounds only conduct electricity in the molten or aqueous state, but not in the solid state?
ions can move in the molten or aqueous state
moving ions carry the electric current

7. Giant Ionic Structures Physical Properties: Solubility
Ionic compounds are soluble in water but insoluble in organic solvents.
ions attract water molecules
disrupts the crystal structure
cause the ions to separate and go into solution

8. Giant Ionic Structures Physical Properties: Volatility
Ionic compounds are not volatile and hence, have no smell.
cannot evaporate easily because of strong ionic bonds holding the ions together
A volatile substance evaporates easily.

9. Giant Ionic Structures Physical Properties: Physical State
Ionic compounds are hard, crystalline solids.
ions held in place by strong ionic bonds, make the crystal hard
ions are arranged in straight rows and form structure with flat sides, resulting in a crystalline structure (flat sides & regular shapes)

10. Compare and Contrast

11. Ionic VS Covalent Ionic Bond Covalent Bond Similarities Differences
Electronic configuration of a noble gas
(PS: Everybody wants to be noble!!)
Differences
Ionic Bond
Covalent Bond
Between positive ions of metals and negative ions of non-metals
Between non-metal atoms
Electrons are transferred
Electrons are shared

12. What to do??

13. Covalent Bonding

14. Covalent Bond: The Definition
A covalent bond is… a bond formed by the sharing of a pair of electrons.

15. More about COVALENT BONDING
Each atom acquires a stable octet structure
Electronic configuration of noble gas (Full shell) = Energetically stable
Formed between atoms of non-metals (but there are exceptions!)
“Spectrum” of bonds

16. Simple Molecular Substances
Consists of small molecules, e.g. bromine

17. Simple Molecular Substances
Within the molecule
Atoms are held together by strong covalent bonds
Between molecules
Weak intermolecular forces (van der Waals’ forces)

18. Iodine, I2
Within each iodine molecule, the iodine atoms are held together by strong covalent bonds.
Between the iodine molecules, there are only weak van der Waals’ forces holding the molecules together.

19. Methane, CH4
In a molecule of methane, CH4, the four C–H covalent bonds are strong.
However, weak intermolecular forces between methane molecules hold them together loosely. Therefore, methane exists as a gas at room temperature and pressure.

20. Physical Properties Physical state Low M.P. & B.P.
Most substances are liquids or gases at room temperature.
Forces between molecules are weak, allowing molecules to move freely.
Low M.P. & B.P.
Little energy required to overcome the (weak) intermolecular forces
(Usually <200°C)

21. Melting & Boiling Points
Covalent substance
Melting point (C)
Boiling point (C)
Carbon dioxide
-56
-79
Chlorine
-101
-35
Hydrogen
-259
-253
Methane
-183
-161
Oxygen
-214
Water
100

22. Physical Properties Volatility Electrical conductivity Solubility
Low B.P. = Volatile
Evaporate easily (to give a smell)
Electrical conductivity
Do not conduct electricity. (Some exceptions, e.g. graphite)
No free-moving ions or electrons to conduct electricity
Solubility
Most molecular substances are insoluble in water, but dissolve in organic solvents. (Some exceptions, e.g. alcohol and sugar, hydrogen chloride)