1. Electrons and Chemical Bonds Part 2
G8 Science
Chapter 8.2

2. Our Story So Far…
What is the difference between a compound and a mixture?
How are covalent bonds formed?
How are ionic bonds formed?
What are valence electrons and what role do they have in chemical bonds?
Explain how to show an ionic bond using Lewis dot diagrams with two Ca and one Cl.

3. Oxidation Numbers
Oxidation numbers tell what the charge of an atom is going to be when it is an ion.
Element on the left of the PT lose electrons so they have a + charge, and an + oxidation number.
Elements on the right of the PT gain electrons so they have a – charge, and a – oxidation number.
Note that this example has the sign
on the left and your book has it on
the right. +1 = 1+
And H can be either +1 or -1

4. Your Turn What is the oxidation number of F?
What is the oxidation number of Li?
What is the oxidation number of C?
What is the oxidation number of He?

5. Oxidation Numbers and Chemical Bonding
The sum of the oxidation numbers in all compounds [ in 8th grade] must be zero.
If you know the elements in a compound:
Find their oxidation number
How many of each you need to make zero?
Try it with Ca and Cl
Ca has an oxidation number of +2
Cl has an oxidation number of -1
Two Cl’s are needed for each Ca
The Chemical formula is CaCl2

6. The Easy Way to Find Formulas using Oxidation Numbers

7. Your Turn
What is the formula for a compound of Hydrogen and Oxygen? [actually practice on this one]
What is the formula for a compound of K and As?
What is the formula for a compound of Al and O?

8. Ionic and Covalent Bonds
What determine whether a bond is ionic or covalent is a donor of electrons or an acceptor of electrons.
A donor and an acceptor makes an ionic bond.
An acceptor and an acceptor makes a covalent bond.

9. Your Turn Will F and Ca form an ionic or covalent bond?
Will O and S form an ionic or covalent bond?
Will Br and O form an ionic of covalent bond?
Will Mg and Br form an ionic or covalent bond?

10. Activity Handout Use the easy way. Due at end of class.
If you get done early, work on homework – do not socialize.