AP®ChemistryCollege BoardStudy GuidesUnit 1: Atomic Structure & PropertiesAtoms & ElectronsElectron Configuration

Electron Configuration (College Board AP® Chemistry) : Study Guide

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Reviewed by: Stewart Hird

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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 equals lambda v where:

    • v is frequency

    • λ is wavelength

    • c is the speed of light which is approximately 3 x 108 ms-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 10-34 J 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 10-19 J

Answer:

  • Step 1: Write down the values and the equations needed

E = 4.81 x 10-19 J

h = 6.626 x 10-34 J s

c =  3 x 108 ms-1

E = hv

c = λv

  • Step 2: Rearrange E = hv in terms of v

E = hv

v equals E over h

  • Step 3: Replace the values and calculate v

 v equals E over h

straight v equals fraction numerator 4.81 space cross times 10 to the power of negative 19 end exponent space straight J over denominator 6.626 space cross times 10 to the power of negative 34 end exponent space straight J space straight s end fraction straight v equals 7.259 space cross times 10 to the power of 14 space straight s to the power of negative 1 end exponent

  • Step 4: Rearrange c = λv in terms of λ

c = λv

lambda equals c over v

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

lambda equals c over v

straight lambda space equals space fraction numerator 3 cross times 10 to the power of 8 space straight m space straight s to the power of negative 1 end exponent over denominator 7.259 space cross times 10 to the power of 14 space straight s to the power of negative 1 end exponent end fraction straight lambda equals 4.13 cross times 10 to the power of negative 7 end exponent space straight 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 (px, py, and pz)

    • 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

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

Electron configuration

  • Electron configuration is a shorthand notation that describes the distribution of electrons in an atom

  • It uses the shell and subshell labels to represent the location of electrons

  • Electrons in the outer shell are called valence electrons

    • The number of principal group in the periodic table is equal to number of valence electrons

  • Electrons in the inner shell are called core electrons

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Author
Reviewer
Martín

Author: Martín

Expertise: Chemistry Content Creator

Martín, a dedicated chemistry teacher and tutor, excels in guiding students through IB, AP, and IGCSE Chemistry. As an IB Chemistry student, he came from hands-on preparation, focusing on practical exam techniques and rigorous practice. While at Universidad San Francisco de Quito, his academic journey sparked a passion for computational and physical chemistry. Martín specializes in chemistry, and he knows that SaveMyExams is the right place if he wants to have a positive impact all around the world.

Stewart Hird

Reviewer: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.

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