Atomic Structure & Periodicity
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Alkali Metals
The group 1 elements — lithium through francium — which have a single valence s electron.
Atomic Structure & PeriodicityAlkaline Earth Metals
The group 2 elements — beryllium through radium — which have two valence s electrons.
Atomic Structure & PeriodicityAtomic Emission Spectrum
The pattern of discrete wavelengths emitted when excited atoms of an element return to lower energy states.
Atomic Structure & PeriodicityAtomic Number
The number of protons in the nucleus of an atom, which uniquely identifies the element.
Atomic Structure & PeriodicityAtomic Orbital
A mathematical function describing the region around a nucleus where an electron of given energy is most likely to be found.
Atomic Structure & PeriodicityAtomic Radius
A measure of the size of an atom, usually taken as half the distance between the nuclei of two bonded identical atoms.
Atomic Structure & PeriodicityAufbau Principle
The rule that electrons occupy the lowest-energy orbital available before filling higher-energy ones.
Atomic Structure & PeriodicityAzimuthal Quantum Number
The quantum number l that determines the shape of an orbital and the magnitude of the electron's orbital angular momentum.
Atomic Structure & PeriodicityBohr Model
The 1913 model in which electrons orbit the nucleus in fixed circular paths of quantised energy and angular momentum.
Atomic Structure & PeriodicityChalcogens
The group 16 elements — oxygen, sulfur, selenium, tellurium and polonium — collectively known as the ore-forming elements.
Atomic Structure & PeriodicityCore Electron
An electron occupying a completely filled inner shell that does not take part in chemical bonding.
Atomic Structure & Periodicityd-Block Elements
The elements of groups 3 to 12, whose valence electrons fill d orbitals of the penultimate shell.
Atomic Structure & Periodicityde Broglie Relation
The relation stating that every particle has an associated wavelength inversely proportional to its momentum.
Atomic Structure & PeriodicityDegenerate Orbitals
Two or more orbitals in the same atom that have exactly the same energy.
Atomic Structure & PeriodicityDiagonal Relationship
The similarity in properties between an element of period 2 and the element one place to its lower right in period 3.
Atomic Structure & PeriodicityDiamagnetism
Weak repulsion from a magnetic field, shown by substances in which all electrons are spin-paired.
Atomic Structure & PeriodicityEffective Nuclear Charge
The net positive charge actually experienced by a particular electron after allowing for shielding by other electrons.
Atomic Structure & PeriodicityElectron
A negatively charged fundamental particle that occupies orbitals around the nucleus and governs chemical bonding.
Atomic Structure & PeriodicityElectron Affinity
The energy change when one mole of gaseous atoms each gains an electron to form gaseous negative ions.
Atomic Structure & PeriodicityElectron Configuration
The notation describing how an atom's electrons are distributed among its available orbitals.
Atomic Structure & PeriodicityElectronegativity
The relative tendency of an atom in a covalent bond to attract the shared pair of electrons towards itself.
Atomic Structure & Periodicityf-Block Elements
The lanthanides and actinides, in which electrons fill the f orbitals of the antepenultimate shell.
Atomic Structure & PeriodicityGroup
A vertical column of the periodic table whose members share the same valence electron configuration.
Atomic Structure & PeriodicityHalogens
The group 17 elements — fluorine through astatine — which are one electron short of a full outer shell.