Chemical Bonding Ionic and Covalent

Chemical Bond Forms between atoms if their valence electrons make a new arrangement that has less energy then their previous arrangement (more stable together than separate) Atoms can lose, gain or share electrons to form bonds

Review: Octet Rule: When atoms combine, bonds form so that each atom finishes with an octet (8) valence electrons

Review: Ionic Bonds: Between cations (+) and anions (-) Is an attraction between oppositely charged ions Metal ion “gives” electrons to non-metal ion Ex : NaCl Na “gives” one e- to Cl

Covalent Bonds Between 2 non-metal ions Share one or more pairs of electrons **A neutral particle that is composed of atoms joined by covalent bonds is called a Molecule. Substances that are composed of molecules are called Molecular Compounds.

Covalent bonding A single bond is formed when one pair of electrons is shared. In a double bond 2 pairs and in a triple bond 3 pairs of electrons are shared Example: diatomic molecules, like O2, H2, N2, F2, Cl2…

Diatomic molecules H· + ·H H:H A diatomic molecule is a molecule made of two of the same atoms. Hydrogen exists as a diatomic molecule. It bonds with itself to form the molecule H2. Electron dot diagram: H· + ·H H:H

Other diatomic molecules: A total of seven elements exist as diatomic molecules rather than as individual atoms. They are; H2, N2, O2, F2, Cl2, Br2, I2 Remember; “HOBrFINCl”….hehe

Single bonds

Lewis structures also called Lewis-dot diagrams are diagrams that show the bonding between atoms of a molecule and other electrons that may exist in the molecule.

Representing Covalent Molecules: No Arrows! Use circles to show shared pairs of electrons Draw electron dot diagrams side by side and see if pairs of electrons can be shared. Remember one electron in pair must come from each atom.

Examples: Br2 O2 N2 CH4 SiH4 CBr4 CBr2F2 H2O CO2 H2S GeH4 C2H2