Atomic Structure & Periodicity — 60 Terms Defined

Heisenberg Uncertainty Principle Atomic Structure & Periodicity J·s The principle that the position and momentum of a particle cannot both be known to arbitrary precision at the same time. Δx · Δp ≥ h / 4π

Hund's Rule of Maximum Multiplicity Atomic Structure & Periodicity Dimensionless The rule that electrons occupy degenerate orbitals singly with parallel spins before any orbital is doubly occupied. maximise total spin S

Inner Transition Element Atomic Structure & Periodicity Dimensionless An element of the lanthanide or actinide series, in which f orbitals are being filled. (n−2)f orbitals filling

Ionic Radius Atomic Structure & Periodicity pm The effective radius of an ion within a crystal lattice, deduced from measured interionic distances.

Ionisation Energy Atomic Structure & Periodicity kJ/mol The minimum energy needed to remove the most loosely held electron from one mole of gaseous atoms in their ground state. X(g) → X⁺(g) + e⁻

Isobar Atomic Structure & Periodicity Dimensionless One of a set of atoms of different elements that share the same mass number but have different atomic numbers. same A, different Z

Isoelectronic Species Atomic Structure & Periodicity Dimensionless Atoms or ions that possess the same number of electrons and the same electron configuration.

Isotone Atomic Structure & Periodicity Dimensionless One of a set of nuclides that contain the same number of neutrons but different numbers of protons. same N, different Z

Isotope Atomic Structure & Periodicity Dimensionless One of two or more atoms of the same element that differ in neutron number and therefore in mass. same Z, different A

Magnetic Quantum Number Atomic Structure & Periodicity Dimensionless The quantum number mₗ that specifies the spatial orientation of an orbital relative to an applied magnetic field. mₗ = −l … 0 … +l

Mass Number Atomic Structure & Periodicity Dimensionless The total number of protons and neutrons in an atomic nucleus. A = Z + N

Metallic Character Atomic Structure & Periodicity Dimensionless The tendency of an element to lose electrons and display typical metallic properties such as lustre, malleability and conductivity.

Metalloid Atomic Structure & Periodicity Dimensionless An element with properties intermediate between those of metals and non-metals, lying along the periodic table's staircase.

Neutron Atomic Structure & Periodicity u An electrically neutral subatomic particle found in the nucleus, with a mass slightly greater than that of a proton. m_n = 1.6749 × 10⁻²⁷ kg

Noble Gases Atomic Structure & Periodicity Dimensionless The group 18 elements, whose completely filled valence shells make them exceptionally unreactive. ns² np⁶ (He is 1s²)

Node Atomic Structure & Periodicity Dimensionless A region within an orbital where the probability of finding an electron falls to zero. total nodes = n − 1

Nucleus Atomic Structure & Periodicity m The dense, positively charged core of an atom, containing virtually all of its mass in protons and neutrons. r ≈ 1.2 × A^(1/3) fm

p-Block Elements Atomic Structure & Periodicity Dimensionless The elements of groups 13 to 18, in which the outermost electrons progressively fill p orbitals. ns² np¹⁻⁶

Paramagnetism Atomic Structure & Periodicity BM Weak attraction into a magnetic field, shown by substances containing one or more unpaired electrons. μ = √(n(n+2)) BM

Pauli Exclusion Principle Atomic Structure & Periodicity Dimensionless The rule that no two electrons in an atom may have the same set of all four quantum numbers. n, l, mₗ, mₛ must differ

Period Atomic Structure & Periodicity Dimensionless A horizontal row of the periodic table, corresponding to one principal quantum number of the valence shell.

Periodic Law Atomic Structure & Periodicity Dimensionless The principle that the properties of the elements are periodic functions of their atomic numbers.

Periodic Table Atomic Structure & Periodicity Dimensionless The tabular arrangement of the chemical elements by increasing atomic number, grouping those with similar properties in vertical columns.

Plum Pudding Model Atomic Structure & Periodicity Dimensionless J. J. Thomson's 1904 model picturing the atom as a sphere of diffuse positive charge with electrons embedded within it.