Electron Configuration (College Board AP® Chemistry)

Study Guide

Written by: Martín

Reviewed by: Stewart Hird

Shells & Subshells

Electrons and Light

Electrons exist in distinct shells within an atom and they can interact with light
Light can behave as a wave or as a particle
Since light can behave as a wave, it has frequency (v) and wavelength (λ)
Frequency and wavelength are related by $c = λ v$ where:
- v is frequency
- λ is wavelength
- c is the speed of light which is approximately 3 x 10⁸ms^-1
Particles of light are called photons
When a photon is absorbed, electrons jump from an inner shell to an outer shell
When a photon is emitted, electrons jump from an outer shell to an inner shell
The energy of the photon (E) is proportional to its frequency (v)
- E α v
The equation used to calculate the energy is E = hv where:
- E is the energy of the photon
- h is the Planck’s constant which is approximately 6.626 x 10^-34J s
- v is the frequency of the photon

Worked Example

Calculate the wavelength of a photon when the energy emitted after an electron transition was 4.81 x 10^-19J

Answer:

Step 1: Write down the values and the equations needed

E = 4.81 x 10^-19J

h = 6.626 x 10^-34J s

c = 3 x 10⁸ms^-1

E = hv

c = λv

Step 2: Rearrange E = hv in terms of v

E = hv

$v = \frac{E}{h}$

Step 3: Replace the values and calculate v

$v = \frac{E}{h}$

$v = \frac{4.81 \times 10^{- 19} J}{6.626 \times 10^{- 34} J s} v = 7.259 \times 10^{14} s^{- 1}$

Step 4: Rearrange c = λv in terms of λ

c = λv

$λ = \frac{c}{v}$

Step 5: Use v calculated in Step 3 to calculate λ

$λ = \frac{c}{v}$

$λ = \frac{3 \times 10^{8} m s^{- 1}}{7.259 \times 10^{14} s^{- 1}} λ = 4.13 \times 10^{- 7} m$

Shells and Subshells

Electrons are organized into shells
- The farther the shell from the nucleus, the higher the energy of those electrons
Each shell contains one or more subshells which are designated as s, p, d, and f
Subshells are further divided into orbitals
Orbitals are regions within a subshell where there is a high probability to find electrons
- The s subshell contains one spherical orbital (spherical shape)
- The p subshell contains three dumbbell-shaped orbitals (p_x, p_y, and p_z)
- The d subshell contains five orbitals, and the f subshell contains seven orbitals
Orbitals can hold a maximum of two electrons

s orbital and p orbital shapes

The s orbital is spherical and the p orbital is a dumbbell shape

The max number of electrons depends on the amount of subshells and orbitals that are held in the shell

Shell number	1	2	3	4
Subshell designation	s	s , p	s , p , d	s , p , d , f
Number of orbitals	1	1 , 3	1 , 3 , 5	1 , 3 , 5 , 7
Max number of electrons	2	8	18	32

Summary of the electronic distribution of an atom