2. Atoms, Elements, and Compounds

3. Chapter Eight: Molecules and Compounds
8.1 Compounds and Chemical Bonds
8.2 Electrons and Chemical Bonds

4. 8.2 Electrons and chemical bonds
Chemical bonds are formed only between the electrons in the highest unfilled energy level.
These electrons are called valence electrons.

6. 8.2 Electrons and chemical bonds
Going from left to right across a period each new element has one more valence electron than the one before it.
How many valence electrons does nitrogen have?

7. 8.2 Lewis dot diagrams
A clever way to keep track of valence electrons is to draw Lewis dot diagrams.
A dot diagram shows the element symbol surrounded by one to eight dots representing the valence electrons.
What is the dot structure for nitrogen?

9. 8.2 Oxidation numbers
An oxidation number indicates the charge on the remaining atom (ion) when electrons are lost, gained, or shared in chemical bonds.
A sodium atom always ionizes to become Na+ (a charge of +1) when it combines with other atoms to make a compound.
Therefore, we say that sodium has an oxidation number of 1+.
What is the most common oxidation number for nitrogen?

11. 8.2 Predicting a chemical formula
When elements combine in molecules and ionic compounds, the total electric charge is always zero.

12. As heat energy is added to ice, the temperature increases until it reaches 0°C.
Then the temperature stops increasing.
As you add more heat, more ice becomes liquid water but the temperature stays the same.
This is because the added energy is being used to break the intermolecular forces and change solid into liquid.
Once all the ice has become liquid, the temperature starts to rise again if more energy is added.

13. As heat energy is added to ice, the temperature increases until it reaches 0°C.
Then the temperature stops increasing.
As you add more heat, more ice becomes liquid water but the temperature stays the same.
This is because the added energy is being used to break the intermolecular forces and change solid into liquid.
Once all the ice has become liquid, the temperature starts to rise again if more energy is added.

14. 8.2 Ionic and covalent bonds
On the periodic table, strong electron donors are the left side (alkali metals).
Strong electron acceptors are on the right side (halogens).
The further apart two elements are on the periodic table, the more likely they are to form an ionic compound.

15. As heat energy is added to ice, the temperature increases until it reaches 0°C.
Then the temperature stops increasing.
As you add more heat, more ice becomes liquid water but the temperature stays the same.
This is because the added energy is being used to break the intermolecular forces and change solid into liquid.
Once all the ice has become liquid, the temperature starts to rise again if more energy is added.

16. 8.2 Ionic and covalent bonds
Covalent compounds form when elements have roughly equal tendency to accept electrons.
Elements that are both nonmetals and therefore close together on the periodic table tend to form covalent compounds.

17. Technology Connection
Spiderman’s Favorite Compound
The physical properties of gold make it useful in surprising ways.
You can find gold in astronaut gear, airplane windshields, and even in some people’s eyelids!