Ochem Basic Concepts to Know

Atomic #

Number of Protons in an atom’s nucleus

Mass #

Number of Protons and Neutrons in an atom’s nucleus

Atomic Weight

Average mass of an element

Molecular Weight

The sum of the atomic weight of all of the atoms in a compound

Ground State Electron Configuration

A complete description of the lowest energy arrangement of electrons around an atom’s nucleus

Aufbau Principle

Fill the lowest energy orbitals first

Pauli Exclusion Principle

Only 2 electrons per orbital and they must go in opposite directions

Hund’s Rule

2 or more orbitals of equal energy will each be ½ filled up before any orbitals of that energy are fully filled up

Bonding Electrons

Valence Electrons involved in bonds

Non-bonding Electrons

Valence Electrons not involved in bonds (Lone Pairs)

Empirical Formula

Lowest Whole-Number Ratio of atoms in a molecule

Molecular Formula

Exact number and identity of the atoms in a molecule

Lewis Dot Structure

Only valence electrons are shown and are represented by dots around the atomic symbol. Electrons in a bond are shown as pairs of 2 dots in between the atomic symbols

Kekule (Line Bond) Structure

Bonding Pairs of electrons are shown as lines between atoms

Formal Charge

Group number of atoms (Normal number of valence electrons) - Nonbonding electrons - Number of bonds

Condensed Structure

Bonds not explicitly shown, Atoms to the right of an atom are assumed to be bonded unless its valence is filled

Skeletal Structure

Atoms other than Carbon and Hydrogen are shown. Carbons are represented by the itnerseciton of lines while Hydrogen isn’t shown at all