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Atomic structure key terms
Study Atomic structure with curriculum-aligned Key Terms resources, practice links, and exam-focused support.
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key terms
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Atomic structure
Key terms
Plum‑pudding model
An early atomic model suggesting a positively charged sphere with embedded electrons.
Gold‑foil experiment
Rutherford’s experiment using α‑particles to probe atomic structure, revealing a small, dense nucleus.
Proton
A positively charged baryon found in the nucleus, with a relative mass of ≈1.007 amu.
Neutron
A neutral baryon in the nucleus, with a relative mass of ≈1.009 amu.
Nucleus
The central part of an atom containing protons and neutrons.
Atomic number
The number of protons in the nucleus, which determines the element.
Isotope
Atoms of the same element with identical proton numbers but differing neutron numbers.
Ion
An atom or molecule that carries a net electric charge due to loss or gain of electrons.
Mass number
The sum of protons and neutrons in an atom’s nucleus, expressed as a whole number.
Isotope
Atoms of the same element that have the same number of protons but different numbers of neutrons, giving different mass numbers.
Isotope
An atom of a given element that has the same number of protons but a different number of neutrons, resulting in a different mass number.
Mass number
The total number of protons and neutrons in an atomic nucleus, expressed as A = Z + N.
Time‑of‑flight (TOF)
The duration an ion takes to travel from the acceleration region to the detector in a mass spectrometer.
Mass‑to‑charge ratio (m/z)
The ratio of an ion’s mass to its charge, a fundamental parameter used to identify ions in mass spectrometry.
Relative Atomic Mass
The weighted average mass of an atom of an element compared to 1/12th of the mass of a carbon-12 atom.
Mass Spectrum
A graphical representation of the mass-to-charge ratios of ions, showing the abundance of each ion.
Isotopic Abundance
The relative proportion of a particular isotope in a naturally occurring sample, expressed as a percentage.
Relative Atomic Mass
The weighted average mass of an element’s isotopes, calculated from their masses and natural abundances.
Mass number
The total number of protons and neutrons in an atom’s nucleus.
Atomic mass
The weighted average mass of all naturally occurring isotopes of an element, expressed in atomic mass units (u).
Subshell
A set of orbitals with the same principal quantum number n and azimuthal quantum number l (s, p, d, f).
Electron configuration
A notation that shows the distribution of electrons among the atomic orbitals of an atom or ion.
Ionisation Energy
The energy required to remove an electron from an atom in the gaseous state.
Nuclear Charge
The total charge of the nucleus, determined by the number of protons.
Ionisation energy
Energy required to remove one electron from a gaseous atom or ion.
Successive ionisation energy
Energy required to remove each successive electron from an atom or ion.
Ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous atoms or ions.
Subshell
A group of orbitals within a shell that share the same angular momentum quantum number l and have a characteristic energy.
Ionisation Energy
The energy required to remove one mole of electrons from one mole of gaseous atoms.
Atomic Radius
The distance from the nucleus of an atom to the outermost shell of electrons.
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