AQA A Level Chemistry: Electron Configuration Flashcards
What is electron configuration?
The arrangement of electrons in orbitals around the nucleus of an atom.
What are the four types of atomic orbitals?
- s-orbital: Spherical, holds 2 electrons.
- p-orbital: Dumbbell-shaped, holds 6 electrons.
- d-orbital: Complex shape, holds 10 electrons.
- f-orbital: Complex shape, holds 14 electrons.
What is the order of filling orbitals?
Orbitals fill in order of increasing energy:
1s \, 2s \, 2p \, 3s \, 3p \, 4s \, 3d \, 4p \, 5s \, 4d \, 5p \, 6s \, 4f \, 5d \, 6p \, 7s
What is the electron configuration of sodium (Na)?
1s^2 2s^2 2p^6 3s^1
Why does the 4s orbital fill before the 3d orbital?
The 4s orbital is lower in energy than the 3d orbital, so it fills first.
What are the exceptions to the usual filling order?
- Chromium (Cr): [Ar] 3d^5 4s^1
- Copper (Cu): [Ar] 3d^{10} 4s^1
These configurations occur because a half-filled or fully-filled d-subshell is more stable.
- Copper (Cu): [Ar] 3d^{10} 4s^1
How do you write shorthand electron configuration?
Use the noble gas from the previous period in square brackets, followed by the remaining configuration.
* E.g., Calcium (Ca): [Ar] 4s^2
What is the electron configuration of a Ti²⁺ ion?
- Titanium: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^2
- Ti²⁺: Remove 2 electrons from 4s first → [Ar] 3d^2
What is the electron configuration of Cl⁻?
Chlorine: 1s^2 2s^2 2p^6 3s^2 3p^5
* Cl⁻: Gains 1 electron → 3p^6 , so the configuration becomes [Ne] 3s^2 3p^6 .
What happens to the electron configuration when transition metals form ions?
Electrons are removed from the 4s orbital first before the 3d orbitals.
What is the electron configuration of Fe³⁺?
- Iron: [Ar] 4s^2 3d^6
- Fe³⁺: Remove 2 electrons from 4s and 1 from 3d → [Ar] 3d^5
What is the maximum number of electrons that can fit into a principal energy level?
{Max electrons} = 2n^2
Where n is the principal quantum number.
