Electron Configuration

Shorthand notation that shows electron arrangement within orbitals Three Rules apply to electron configuration: 1.Pauli exclusion Principle: No two electrons can have the same four quantum numbers

2. Aufbau Principle: Orbitals of lowest energy are filled first. An orbital cannot take more than 2 electrons.

3. Hund’s Rule: Every orbital in a subshell is occupied by one electron before any one can gain two. – All electrons in singly occupied orbitals have the same spin (up first, then down) – Ex: Nitrogen – 7 atoms 1s 2 2s 2 1p 3

Three types of Electron Configuration 1.Energy Level Diagrams – Represent each electron by an arrow (place in lowest orbitals first) – The direction of the arrow represents the electron spin – Orbitals must be filled before moving on to the next orbital – each orbital receives one electron before pairing occurs (Hund’s Rule) – Draw an up arrow to show the first electron in each orbital (same spin)

Example: Electron Configuration of Carbon

Energy level Diagrams of Ions Anions: – Negatively charge – Add extra electrons following the rules Cations: – Positively charged – Draw a neutral atom then subtract the required number of electrons starting at the highest orbital and working down

2. Complete Electron Configuration 1.Start with the principle quantum number (n) 2.Place the orbital shape (l) beside it 3.Add the # of electrons as a superscript on (l) ** The sum of the superscripts = number of electrons Ex: Fluorine - 9 electrons 1s 2 2s 2 2p 5

3. Condensed Electron Configuration Write out an Electron Configuration, referring to the previous noble gas 1.Write the previous noble in square brackets 2.Continue electron configuration until you reach proper number of electrons for the element. Aluminum = 13 electrons [Ne] 3s 2 3p 1