Section 4: Electron Configurations

1sorbital

2sorbital

2porbitals

3sorbital

Nucleus

Electron energy levels have sublevels of different shapes

3 principles Describe the electron configurationof any atom:•the aufbau principle•the Pauli exclusion principle•and Hund’s rule

Electron Configurations:location of e–’s in different orbitals

How do electrons fill these orbitals?

Aufbau Principle

(building up), electrons fill the orbitals of lowest energy first.

Pauli Exclusion Principle

an atomic orbital may describe at most two electrons that must have opposite spins; that is, the electron spins must be paired.

↑↓s

Hund’s Rule

electrons occupy orbitals of the same energy with as many of the same spin as possible before opposite spin.

↑↑ ↑↓↓px py pz

↓

Element # of electrons

Orbital notation Electron configuration

Lithium 3 ____ ____ ____ ____ ____ 1s 2s 2p

1s22s1

Beryllium 4 ____ ____ ____ ____ ____ 1s 2s 2p

1s22s2

Boron 5 ____ ____ ____ ____ ____ 1s 2s 2p

1s22s22p1

Carbon 6 ____ ____ ____ ____ ____ 1s 2s 2p

1s22s22p2

Nitrogen 7 ____ ____ ____ ____ ____

1s 2s 2p

1s22s22p3

Oxygen 8 ____ ____ ____ ____ ____ 1s 2s 2p

1s22s22p4

Fluorine 9 ____ ____ ____ ____ ____ 1s 2s 2p

1s22s22p5

Neon 10 ____ ____ ____ ____ ____ 1s 2s 2p

1s22s22p6

2s21s2 3s23p32p6

Write the electron configuration for phosphorus (P):

nucleus

Write the electron configuration for phosphorus (P):

nucleus

2s21s2 3s23p32p6

valence electrons:e–’s in the outer most (highest) energy level

How many valence e–’s in phosphorus (P)? 5

nucleus

Write the electron configuration for Krypton (Kr):

2s21s2 2p6 3p63s2 4p64s2 3d10

nucleus

Write the electron configuration for Krypton (Kr):

2s21s2 2p6 3p63s2 4p64s2 3d10

valence electrons:e–’s in the outer most (highest) energy level

How many valence e–’s in Krypton (Kr)? 8

1. Identify the element that corresponds to the following electron configuration: 1s22s22p63s2

A. Ca

B. Ne

C. Na

D. Mg

Quick Quiz!

Quick Quiz.

2. Write the electron configuration for the atom N.

A. 1s22s22p5

B. 1s22s22p3

C. 1s22s1p2

D. 1s22s22p1

Quick Quiz.

3. What is the first (lowest-numbered) principal energy level in which p orbitals are found?

A. 1

B. 2

C. 3

D. 4

• The period number tells you the energy level (remember, the d block is one energy level lower).

• The group # tells you the # of valence electrons.

• Group 1 elements have 1.

• Group 7A have 7.

Electron Configurations and the Periodic Table

Noble Gas Core Configuration

Na: 1s2 2s2 2p63s1

Ne: 1s2 2s2 2p6

Noble gas e- config for Na:

[Ne]3s1

Ne

Noble Gases are group 18

4p12s21s2 2p6 3p63s2 4p14s23d10

OR 4s2[Ar] 3d10

Write the full electron configuration for Gallium (Ga), atomic number 31.

Ar

Phosphorus (P):

Lewis dot diagrams

[Ne]3s2 3p3

1s2 2s2 2p6 3s2 3p3

# valence e–’s: ___

Group # : ___

5

5A

P

Lewis dot diagram:

• valence e–’s are shown as dots around the symbol of the element

Lewis dot diagrams

Bromine (Br):

[Ar]4s2 3d10 4p5

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5

# valence e–’s: ___

Group # : ___

7

7ALewis dot diagram: Br

• valence e–’s are shown as dots around the symbol of the element