Electron Configurations

Objectives:3.0 Use the periodic table to identify

periodic trends, including atomic radii, ionization energy, electronegativity, and

energy levels.

3.1 Utilizing electron configurations, Lewis dot structures, and orbital

notations to write chemical formulas

Ground State Electron Configurations

• Electron configuration: the arrangement of electrons in an atom

• What is “ground state”?

• Three rules define how electrons are arranged in an atom’s orbitals:1. The aufbau principle

2. The Pauli exclusion principle

3. Hund’s rule

The Aufbau Principle• Each electron occupies the lowest energy

orbital available, according to the aufbau diagram:

The Pauli Exclusion Principle• A maximum of 2 electrons may occupy a

single atomic orbital, but ONLY if the electrons have opposite spins (represented by ↑ and ↓).

Hund’s Rule• Single electrons with the same spin must

occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbitals (i.e., 1 ↑ in each 3p orbital BEFORE a ↓ can pair up with a ↑ in an orbital).

Orbital Diagrams and Electron Configuration Notations

• These are just 2 different ways to represent an atom’s electron configuration.

Orbital Diagrams:

• Have a box for each of the atom’s orbitals.• Boxes contain either ↑ (1 electron), or ↑↓

(full orbital), or may be empty.• Each box is labeled with the principal

quantum number and the sublevel associated with the orbital.

• Examples on board

Electron Configuration Notation

• Shorthand to designate all electrons and their orbitals

• Designates principal energy level and sublevel, and includes a superscript to show the number of electrons in the orbital.

• Example: Carbon 1s22s22p2

• What is the electron diagram for carbon?

• Table 5-3, p.137

Electron Configuration Notation (cont.)

• What is the electron configuration notation for the following elements?a. Helium

b. Neon

c. Argon

d. Krypton

e. Xenon

f. Radon

• What do these elements have in common?

Electron Configuration Notation (cont.)

• Electron configuration notation can be abbreviated by noble-gas notation.

• [He] = 1s2

• [Ne] = 1s22s22p6

• So magnesium can be written:– 1s22s22p63s2 -OR-– [Ne]3s2

• How would you write phosphorous?