Electron Configuration and Chemical Bonding Basics

Electron Spin and Orbitals

Spin refers to the movement of an electron around the nucleus and on its own axis. There are two possible spin directions: +1/2 and -1/2. When two electrons have opposite directions of rotation, they are represented with small arrows, one pointing up and the other down.

An orbital is occupied when it contains two electrons. An orbital with a single unpaired electron is represented by a single arrow. Orbitals are represented as rectangles called quantum boxes, within which the electrons are indicated.

The electronic configuration of an atom describes how the electrons are arranged within the atom.

Hund's Rule

Hund's rule states that an electron cannot completely fill an orbital until all orbitals within that sublevel contain at least one electron.

Oxidation State and Valence

Oxidation state is the number of electrons an element gains, loses, or shares to achieve a more stable configuration.

The valence of an element is its combining capacity relative to hydrogen, which is taken as unity.

Octet Theory

The Octet Theory is based on the observation that noble gases have a very stable electronic configuration. Since all noble gases have eight valence electrons, it is considered that an outer shell with eight electrons is the most stable configuration for atoms.

Electronegativity

Electronegativity is the relative power of attraction that an atom has for a pair of electrons shared in a chemical bond.

Ionic Bonds

The valence unit of an ionic bond is equal to the number of electrons transferred or accepted. An ion can be an electropositive cation or an electronegative anion.

Covalent Bonds

Covalent bonds are chemical bonds formed by the sharing of an electron pair.

Intermolecular Forces

Van der Waals Forces

Van der Waals forces are divided into:

1. Dipole-dipole forces: These occur when neutral polar molecules approach each other.

• Attractive forces: Polar molecules attract each other when the positive end of one molecule is attracted to the negative end of another.
• Repulsive forces: These occur when two positive or two negative ends of molecules approach each other.

London dispersion forces: Gases can be liquefied, which means there must be attractive forces between their molecules. These attractive forces are called London dispersion forces.

Hydrogen Bond

A hydrogen bond is a special type of intermolecular attraction between a hydrogen atom in a polar bond and an unshared electron pair of an electronegative atom in a neighboring molecule.