SCH4U - Chemistry 12 (2024-25) - A

Summary

• n-values: Describe an orbital shell
• Each shell contains subshells
• Subshell = orbital
• Every orbital can have 2 electrons
• Every shell can have n² orbitals
• Every shell can have 2n² electrons

• The 4 quantum numbers used to describe an electron are as follows:
  • Principal Quantum Number (n): Describes the distance of a shell from the nucleus
  • Secondary Quantum Number (l): Describes the shape of an orbital (subshell)
  • Magnetic Quantum Number (m_l): describes the orientation of the orbital in space (ie. what axis does it lie on)
  • Spin Quantum Number (m_s): describes the direction an electron is spinning

• n = 1 shell has 1 s-orbital
• n = 2 shell has 1 s-orbital and 3 p-orbitals
• n = 3 shell has 1 s-orbital, 3 p-orbitals and 5 d-orbitals
• n = 4 shell has 1 s-orbital, 3 p-orbitals, 5 d-orbitals and 7 f-orbitals

• The secondary Quantum Number (ℓ) describes the name and shape of an orbital
• ℓ-values range from 0 to (n-1)
• ℓ = 0: s-orbital
• ℓ = 1: p-orbital
• ℓ = 2: d-orbital
• ℓ = 3: f-orbital

• When ℓ = 0: (m_l) values range from 0 to 0; therefore there is 1 s-orbital in every shell
• When ℓ = 1:(m_l) values range: -1, 0, 1; therefore there are 3 p-orbitals in every shell from n = 2 and above
• When ℓ = 2:(m_l) values range: -2, -1, 0, 1, 2: therefore there are 5 d-orbitals in every shell from n = 3 and above
• When ℓ = 3:(m_l) values range from -3, -2, -1, 0, 1, 2, 3: therefore there are 7 f-orbitals in every shell from n = 4 and above

• m_s values indicate the spin of an electron, values can only be -1/2 or +1/2
  
• 2 electrons in the same orbital must have opposite (m_s) values

• The Pauli Exclusion Principle tells us that 2 electrons in the same orbital cannot have the same spin value.

The table below summarizes all the information you will need for the section on quantum numbers: