Handout three Handout on Bonding What’s Cookin

Three Types of Chemical Bonding, Kinda

Ionic Bond: Electrostatic attraction between oppositely charged ions.

Coulomb’s Law: This allows us to calculate the energy of interaction between a pair of ions.

Metallic Bonding: Atoms are held together by metallic bonding. The valence electrons of the metal atoms are free to move, they are not confined to individual atoms or bonds. “A lattice of positive ions bathed by a sea of electrons.

Covalent Bonds: When two atoms share a pair of electrons.

Nonmetallic atoms are linked together by shared pairs of electrons in units called molecules.

Polar covalent bonds: A bond in which the electron density is not shared equally. The bonding electrons spend more time “nearer” to one of the atoms in the bond.

Electronegativity: A measure of the attractive forces that an atom exerts on a shared electron pair in a chemical bond. The differences in electronegativity (EN) between the two bonded atoms offer an indication of the polarity in the bond.

Lewis Symbols: The chemical symbol of an element with a dot for each valance electron.

Lewis Structure: A diagram showing how electron pairs are shared between atoms in a covalent molecule.

1. Valence Shell Electron Pair Repulsion Theory: (VSEPR)

all atoms want octets (or duets for hydrogens)

all atoms and electron pairs arrange themselves to minimize interactions

2. Valance Bond Theory

all atoms want octets

introduces concept of hybridization to explain why all C--H bonds are equivalent in methane (CH₄), for example.

Hybridization is the mixing of atomic orbitals (AO) to form new atomic orbitals, hybrid orbitals.

Resonance Structures are necessary when using Valance Bond Theory.

Resonance Structures are written for compounds whose properties are NOT adequately described by a single Lewis structure. Resonance Structures are NOT in equilibrium. They are alternative descriptions of a single species. Resonance Structures may be derived by use of the arrow formalism method. Electrons move, NOT atoms! Identical Resonance Structures have equal importance.

3. Molecular Orbital Theory

Molecular Orbital theory says that when two atomic orbitals come together we get two new molecular orbitals. We no longer have AO involved in bonding. They disappear. The need for resonance structures and such are no more. This theory can be very accurate, however, is based on mathematics and computers are needed, and we will not due until later, for it is good for some things. Maybe we do H₂ and He₂ now?