2. Atoms, Elements, and Compounds

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

4. 8.1 Compounds and chemical bonds
A compound contains two or more different elements that are chemically bonded together.

5. 8.1 Compounds and chemical bonds
A mixture contains two or more elements and/or compounds that are not chemically bonded together.

6. 8.1 Molecules and covalent bonds
A chemical bond forms when atoms transfer or share electrons.
A covalent bond is formed when atoms share electrons.
Low melting and boiling points

7. Covalent Bonds Elements that share electrons are typically non-metals.
They will share electrons until their outer energy level is full (typically 8)
For Example: Oxygen will share electrons with two hydrogen atoms, each hydrogen bringing one electron and oxygen bringing 6.

8. 8.1 Chemical formulas and diagrams
All Compounds are represented by a chemical formula.
The chemical formula tells you the precise number of each kind of atom in the compound.

10. 8.1 Structure and function
The properties of a compound depend MUCH more on the exact composition and structure (shape) of its molecule than on the elements of which it is made.

11. 8.1 Ionic bonds
Ionic bonds are bonds in which electrons are transferred from one atom to another.
Sodium and chlorine form an ionic bond because the positive sodium ion is attracted to the negative chloride ion.

12. Ionic Bonds
Transfer of electrons occurs between a metal and non-metal typically.
The metals donate electrons and become + ions.
The non-metals receive electrons and become – ions.
Metals tend to empty their outer shell while non-metals fill their outer shell.

14. 8.1 Why chemical bonds form
It takes energy to separate atoms that are bonded together.
The same energy is released when chemical bonds form.
Atoms form bonds to reach a lower energy state.

15. The closer an element is to having a “full shell” of electrons, like a noble gas, the more reactive the element is. Elements will either gain, lose or share electrons to get to that full state.