1. How Atoms Combine

2. Compounds Two or more elements joined in definite proportion
Atoms join to become stable
Created by bonds between elements
Bonds represent energy-electrical forces
Symbolized by a formula
Example: Water, H2O
(Two hydrogen atoms and one oxygen atom)

3. Chemically Stable Atoms
Electrons in outer most energy level are called “Valence Electrons”
Certain electron arrangements are more stable than others
Stable if outer energy level is filled
If unfilled then the element will form a chemical bond
Bond by gaining, losing, or sharing electrons
Chemical Bonding

4. Valence Electrons Lewis Dot Diagrams
Examples of Noble Gases Show filled outer energy levels
Sodium & Chlorine fill the outer energy levels by transferring electrons.

5. Bonding Capacity Also called valence
Indicate how many electrons an atom may gain, lose, or share when bonding
Found in Periodic Table or in charts
Used to write formulas for binary compounds

6. Ionic Bonds Electrons are transferred between atoms
One atom gains while the other loses
Atoms are no longer neutral and have a charge; + or -
Ion—element with a charge
Ionic bond—force of attraction between opposite charges

7. Ionic Bonds Cont’d For example Na can donate 1 electron to Cl
Makes Na+1 and Cl-1
Held together by strong electrostatic attractions
Ionic solids like salt are soluble in water

8. Covalent Bonds Electrons are shared between atoms
Occurs in atoms that do not easily lose electrons
Positive nucleus of each atom has an equal attraction to shared electrons
This attraction holds the atoms together
Bonding forms molecules

9. Example of Covalent Bonding
Methane makes four covalent bonds. Each diagram represents the same molecule—CH4

11. Covalent Bonds Cont’d Can occur between atoms of same element
Seven diatomic molecules—two atoms
Found in nature as two atoms covalently bonded
Diatomic Molecules
Hydrogen—H2
Nitrogen—N2
Oxygen—O2
Fluorine—F2
Chlorine—Cl2
Bromine—Br2
Iodine—I2

14. Naming Binary Compounds
Write name of first element (more left on periodic table)
Write root name of second element
Add –ide ending to the root
MgCl2 Magnesium Chlor- -ide