Atomic Structure & Periodicity — 8 Terms Defined

Alkali Metals Atomic Structure & Periodicity Dimensionless The group 1 elements — lithium through francium — which have a single valence s electron. ns¹

Alkaline Earth Metals Atomic Structure & Periodicity Dimensionless The group 2 elements — beryllium through radium — which have two valence s electrons. ns²

Atomic Emission Spectrum Atomic Structure & Periodicity nm The pattern of discrete wavelengths emitted when excited atoms of an element return to lower energy states. ΔE = hν

Atomic Number Atomic Structure & Periodicity Dimensionless The number of protons in the nucleus of an atom, which uniquely identifies the element. Z = number of protons

Atomic Orbital Atomic Structure & Periodicity Dimensionless A mathematical function describing the region around a nucleus where an electron of given energy is most likely to be found. |ψ|² = probability density

Atomic Radius Atomic Structure & Periodicity pm A measure of the size of an atom, usually taken as half the distance between the nuclei of two bonded identical atoms. r = d(X–X) / 2

Aufbau Principle Atomic Structure & Periodicity Dimensionless The rule that electrons occupy the lowest-energy orbital available before filling higher-energy ones. fill in order of increasing (n + l)

Azimuthal Quantum Number Atomic Structure & Periodicity Dimensionless The quantum number l that determines the shape of an orbital and the magnitude of the electron's orbital angular momentum. l = 0 to (n − 1)