Writing Electron Configuration

Quantum Numbers Quantum numbers define the location of electrons in an atomic orbital. This helps us understand why different atoms exhibit certain properties, such as size and reactivity. Quantum numbers are written like this: (2,1,-1,-½) where (n, /, m /, m s ) They are like an “address”

n = main energy level (principal quantum number) / = orbital shape (angular momentum quantum number) m / = orientation of orbital (magnetic quantum number) m s = electron spin (spin quantum number)

n (1, 2, …)/ (0, 1,…n-1)m (or m / ) -/ to +/ Orbital name # of orbitals 1001s1 2002s1 21-1,0,12p3 3003s1 31-1,0,13p3 32-2, -1,0,1, 23d5 4004s1 41-1,0,14p3 42-2, -1,0,1, 24d , -1,0,1, 2, 34f7 Quantum Numbers for the First 30 Orbitals

Writing Electron Configuration It’s useful to be able to write out the location of electrons in an atom. Si: 1s 2, 2s 2, 2p 6, 3s 2, 3p 2 There are three rules that govern electron configuration.

Aufbau Principle “Aufbau” is German for building up. Each electron occupies lowest energy state available Energy states roughly relate to period.

Memorizing Orbital Filling Order

Pauli Exclusion Principle No two electrons may have the same 4 quantum numbers. This means: Maximum of 2 electrons occupy a single atomic orbital The 2 electrons must have opposite spins, represented by up/down arrows.

Hund’s Rule Each equal-energy orbital gets one helping of electron before any orbital gets a second helping. This is evident in Orbital Diagrams

Orbital Diagrams