Electron configurations show number and location of electrons in atoms. Principal quantum number (n) indicates main energy level. Each orbital can accommodate maximum two electrons. Orbitals are shown as squares with electrons as arrows
Effective nuclear charge (Zeff) is the number of elementary charges an electron experiences by the nucleus. Shielding effect prevents higher energy electrons from experiencing full nuclear charge. Effective nuclear charge is also called core charge
MOT was developed by Hund and Mulliken in early twentieth century. Theory explains molecular bonding better than valence-bond theory. Total molecular orbitals equal total atomic orbitals formed
Atomic orbitals increase in energy with increasing principal quantum number (n). Electrons fill orbitals in order s < p < d < f. Electrons in s orbitals are least penetrating and least stable
Electrons fill lowest energy levels first in atomic orbitals. Principle developed by Bohr and Pauli in early 1920s. Electrons fill orbitals in ascending order of energy. Principle follows Madelung's rule: energy increases with n+l
Orbitals are three-dimensional regions around an atom's nucleus. Only two electrons can exist in an orbital space. Electrons with same n value are in the same shell