Electron configuration
High School
Definition
The arrangement of electrons in an atom's shells and subshells. Electrons fill the lowest available energy levels first, and the configuration of the outermost electrons largely determines an element's chemical properties and its place in the periodic table.
Worked examples
\(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5\)
Bromine (35 electrons) fills orbitals in order of increasing energy; note that 4s fills before 3d.
\(1s^2 2s^2 2p^6\)
Neon has a filled outer shell (8 valence electrons), making it a stable noble gas.
\([Ne] 3s^2 3p^1\)
Aluminum's configuration in shorthand notation: the neon core plus three valence electrons.
Common mistakes
- \(1s^2 2s^2 2p^6 3d^{10} 4s^2\) → \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10}\) The 4s orbital fills before 3d, and you must write them in energy order (or by shell number).
- Carbon: \(1s^2 2s^2 2p^2\) means 2 electrons in one p orbital → The 2 electrons spread into separate p orbitals (Hund's rule) Electrons fill degenerate orbitals singly before pairing up to minimize repulsion.
- The superscript is the number of protons in that orbital → The superscript is the number of electrons in that subshell Configuration describes electron distribution, not protons.
Where you'll use it next
You'll use electron configurations to predict chemical bonding and reactivity, draw Lewis structures, understand periodic trends like ionization energy, and explain the behavior of ions and transition metals in chemistry.
Found in 1 StudyPug lesson
Unraveling Subshells: The Building Blocks of Electronic Structure
11th Grade11thChemistry 11
Dive into the world of electron subshells! Discover how these fundamental components shape atomic structure, influence chemical properties, and form the basis for advanced chemistry concepts.
See also
Reviewed by Pat Cheng, M.Ed. — StudyPug Curriculum Lead · Last updated June 6, 2026