Valence electrons — Science definition
Electrons relevant to the chemical bonding model. Main-group outer-shell patterns are a useful case; transition elements can involve nearby d states.
Where it is taught
- Electron Configuration — Atoms, Electrons & Periodicity, Physical Science: Chemistry, Grade 11
In use
For main-group elements, valence electrons are usually the electrons in the outermost occupied shell.
Electron Configuration
Questions using valence electrons
Problem 1
Bromine (Z = 35) has the configuration [Ar] 4 s² 3d¹⁰ 4p⁵. How many valence electrons does it have?
Answer and explanation
7
Valence electrons are those in the highest energy level (n = 4): 4 s² + 4p⁵ = 7. The inner 3d¹⁰ electrons are core, not valence.
Problem 2
Sulfur's configuration is 1 s² 2 s² 2p⁶ 3 s² 3p⁴. How many valence electrons does it have?
Answer and explanation
6
Valence electrons are those in the highest level (n = 3): 3 s² 3p⁴ = 6.
Taught alongside
- energy level (n)
- sublevel
- orbital
- electron configuration
- Aufbau principle
- Pauli exclusion principle
- Hund's rule