Chemical Bonding and Molecular Geometry

A collection of vocabulary flashcards covering key concepts in chemical bonding and molecular geometry.

Octet Rule

The principle that atoms tend to bond in such a way that they have eight electrons in their valence shell.

Lone Pair

A pair of valence electrons that are not shared with another atom.

Formal Charge

A hypothetical charge an atom would have if all bonding electrons were shared equally.

Resonance

The phenomenon where multiple valid Lewis structures can represent a molecule, indicating that the real structure is an average of these

Bond Energy

The energy required to break a specific covalent bond in one mole of gaseous molecules.

VSEPR (Valance shell electron pair repulsion) Theory

A theory that predicts the geometry of individual molecules from the number of electron pairs surrounding their central atoms.

exception when drawing lewis structures

Free radicals: odd # of valance

Electron deficient Molecules: there isn’t enough for 8

Hypervalent molecules: period 3 or higher can have more than 8

Formal charge rules

1. 0 is preferable

2. fewest not 0’s

3. adjacent charges are 0 or opposing signs

4. neg. formal charges on more EN atoms

Bond strength trends

1. increases with # of electrons shared

2. decreases with increasing bond strength (1 A = 0.1 nm)

3. Between 1 and group elements, decreases down a group

lattice energy

strength of attraction between ions in ionic compounds

endothermic

C (crystal), R (distance), Z (charge)

bond angle

the angle between two bonds in a molecule, influenced by molecular geometry.

bond distance

distance between two nuclei

strength varies as:

lone pair - lone pair > lone - bonding pair > bonding pair - bonding pair

for a molecule to be polar

must have at least 1 polar covalent bond AND have a molecule structure that the dipole moments do not cancel out each other