Electron Configuration

Quantum number n

Determines the energy of the orbital; energy increases as this number increases

Quantum number I

Specifies the possible orbital shapes for a given n. For a given n, l = 0, 1, 2,… n-1.

• l = 0 | s orbital (1 orbital)

• l = 1 | p orbital (3 orbitals)

• l = 2 | d orbital (5 orbitals)

• l = 3 | f orbital (7 orbitals)

Quantum number m_l

Specifies which of the orbitals corresponds to a particular electron.

m_l = -l,….. -1, 0, 1,…., l

Quantum number m_s

Electron spin | can take one of two values: +1/2 or -1/2

Atomic orbital shapes

• s orbitals are spherical

• p orbitals are dumbbell shaped; x, y, z

• d orbitals are clover-shaped

The Pauli Exclusion Principle

No two electrons can have the same four quantum numbers. An orbital can hold at most two electrons, and then only if the electrons have opposite spin

Aufbau principle

The ground state configuration is determined by filling orbitals with the lowest energy

Hund’s Rule

The lowest energy arrangement of electrons in a subshell is obtained by putting electrons into separate orbitals with the same spin before pairing them

Exception to the Building-up principles

Elements whose electron configuration ends in d4 become d5 (half-filled), and those with d9 become d10 by getting one electron from the last level

Electron configuration shortcut in periodic table

• Far left; 1-7s

• Middle; 3-6d

• Right; 2-7p

• Bottom; 4-5f

Order of increasing atomic radius

Order of increasing ionization energy

Order of increasing electron affinity