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 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
- Step 3: Replace the values and calculate v
- Step 4: Rearrange c = λv in terms of λ
c = λv
- Step 5: Use v calculated in Step 3 to calculate λ
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
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