1. Chemicals of the Natural Environment.
Lesson 2a

2. Learning objective: To understand the properties of simple covalent compounds.
Must: Know what air contains.
Should: Know the properties of covalent compounds.
Could: Explain the properties of simple covalent compounds.
Starter: What gases are found in air?
Keywords: Elements, compounds, molecules, formula, covalent bonds, sharing, intermolecular forces and properties.

3. So what’s in air? Oxygen. Nitrogen. Carbon dioxide. Water. Argon.
What about dry air?
The same apart from water.

5. Elements or compounds? Oxygen. Nitrogen. Carbon dioxide. Argon.
Sort the above into elements and compounds?
Elements contain only one type of atom; Oxygen, nitrogen and argon.
Compounds contain at least 2 different types of atom in a fixed ratio; Carbon dioxide.

6. Molecules.
A molecule is any substance that contains more than one atom. It can be either a compound and sometimes an element.
Which is not a molecule?
O2.
N2.
CO2.
Ar.
Ar – it exists as an atom on its own.

7. Composition of air. Remember it mainly consists of nitrogen (78%)
and oxygen (21%).

8. It’s good to share.
The other way that atoms can gain a full outer shell of electrons is by sharing their outer electrons.
This happens between non-metal atoms.

9. Click for another example
Hydrogen and Hydrogen H H H2
Click for another example
Click for animation

10. Nitrogen and Hydrogen (Ammonia)
NH3 H
Click for another example
Click for animation

11. Hydrogen and Oxygen O H2O H H Click here to return to bonding options
Click for animation

12. Learning objective: I can explain the properties of simple covalent compounds.
Must: Know what air contains.
Must: Be able to identify covalent compounds.
Should: Know the properties of covalent compounds.
Could: Explain the properties of simple covalent compounds.
Starter:
Keywords: Elements, compounds, molecules, formula, covalent bonds, sharing, intermolecular forces and properties.

13. Covalent (molecular) bonding
The covalent bonding arises from the electrostatic attraction between the nuclei of the atoms and the electrons shared between them (green lines).

14. Simple covalent compounds.
Covalent bonds are strong, but there are weak forces of attraction between individual molecules.

15. Explaining the properties
Why are a lot of simple covalent compounds gases and liquids at room temperature?
They have low melting and boiling points.
Why do they have low melting and boiling points.
This is because of the weak intermolecular forces between covalent compounds.

16. Explaining the properties
Why can’t covalent compounds conduct electricity?
This is because there are no free electrons, they have no charge.
Now let’s look at how covalent bonds are formed, remember the non-metal atoms share electrons to gain a full outer shell.