1. Chemical Formulas
& Compounds

2. Chemical Bonds
When two atoms move close together, their valence electrons interact.
A chemical bond will form if the new arrangement of electrons and atoms is stable.
Atoms, ions and compounds are most stable when the atoms involved have the same arrangement of valence electrons as the nearest noble gas on the periodic table. (i.e.: a full valence shell also called a “stable octet.”)
Ted-Ed: How Atoms Bond

3. Types of Bonds There are three main types of bonds: Ionic Bonds:
between cations and anions, (generally metals and non-metals)
2. Covalent Bonds:
between non-metal atoms
3. Metallic Bonds:
between metal atoms

4. Ionic Bonding
The non-metal atom “steals” an e- from the metal atom - +
The non-metal becomes a (-) ion and the metal becomes a (+) ion
Since they are oppositely charged ions, they attract each other and stick together
Na & Cl
They will form a “crystal lattice” structure rather than separate molecules

5. Electrons are transferred from the cations to the anion
e.g.: lithium and oxygen form an ionic bond in the compound Li2O +
Lithium
Oxygen
Electrons are transferred from the cations to the anion 1+ 2- 1+
Li2O has a ratio of 2:1 as shown. Each crystal of Li2O has one oxygen ion for every two lithium ions.
Li+
O2-
Li+
Lithium oxide, Li2O

6. Covalent Bonding
In covalent bonding, atoms overlap slightly, and one unpaired electron from each atom will pair together.
A covalent compound is formed when non-metallic atoms share electrons.
A covalent bond forms molecules and have definite structures with exact numbers of each atom.
A shared pair of electrons is called a “bonding pair.”
A pair of electrons in the valence shell that is not used in bonding is called a “lone pair.”

7. e.g.: Hydrogen and oxygen form a covalent bond in the compound H2O+
Hydrogen
Oxygen
Bonding pair
Lone pair
Each molecule of H2O has exactly one oxygen atom bonded with two hydrogen atoms.

8. Lewis Diagrams of Compounds Ionic Bonds Covalent Bonds
Mg: atomic number 12  2 electrons on valence shell
Oxygen atomic number 8  6 electrons on valence shell
Bromine atomic number
Bromine  7 electrons on valence shell; barium: 2 electrons on valence shell
Covalent Bonds

9. Assignment
Homework:
Worksheet on Bonding