Orbitals are regions of space where an electron is most likely to be found. They are described by quantum numbers and can hold up to two electrons with opposite spins. The arrangement of electrons in orbitals is known as the electron configuration.
Atomic orbitals are associated with individual atoms and describe the location of electrons within an atom. Molecular orbitals are formed when atomic orbitals from different atoms combine and describe the location of electrons in a molecule.
Hybridization is the mixing of atomic orbitals to form new hybrid orbitals, which are used to describe the bonding in molecules. It is important in understanding molecular geometry because the type of hybridization (sp, sp2, sp3, etc.) determines the shape of the molecule.
The octet rule states that atoms tend to gain, lose, or share electrons in order to have a full outer energy level with 8 electrons. Hybridization allows atoms to achieve this octet by forming bonds and sharing electrons.
In molecules with double or triple bonds, hybridization allows for the formation of multiple bonds by mixing different types of orbitals. For example, in a molecule with a double bond, one sigma bond is formed from the overlap of two hybrid orbitals and one pi bond is formed from the overlap of two p orbitals.