Atomic Structure and Isotopes – Core Vocabulary

Vocabulary flashcards covering key terms from the lecture on atomic structure, sub-atomic particles, isotopes, and mass spectrometry.

Proton

Sub-atomic particle with a relative mass of 1 u and a positive charge of 1 +; located in the nucleus.

Neutron

Neutral sub-atomic particle with a relative mass of 1 u; found in the nucleus and contributes to atomic mass.

Electron

Negatively charged sub-atomic particle (1 –) with negligible mass (≈1⁄1836 u) that orbits the nucleus in shells.

Atomic Number (Proton Number)

The number of protons in the nucleus of an atom; uniquely identifies an element on the periodic table.

Relative Mass

A comparison of sub-atomic particle masses using the proton’s mass as the reference value of 1.

Relative Charge

Simplified charge scale assigning 1 + to a proton, 1 – to an electron, and 0 to a neutron.

Isotope

Atoms of the same element that have identical proton numbers but different numbers of neutrons and therefore different masses.

Relative Isotopic Mass

Mass of a particular isotope relative to 1⁄12 of the mass of a carbon-12 atom.

Relative Atomic Mass (Ar)

Weighted mean mass of an element’s atoms relative to 1⁄12 of the mass of a carbon-12 atom.

Atomic Mass Unit (u)

Standard mass unit equal to 1⁄12 of the mass of a carbon-12 atom (≈1.661 × 10⁻²⁷ kg).

Mass Defect

The small amount of mass lost when protons and neutrons are bound together by the strong nuclear force.

Strong Nuclear Force

Attractive force that holds protons and neutrons together in the nucleus, overcoming electrostatic repulsion.

Mass Spectrometer

Instrument that determines isotopic masses and abundances by ionising, accelerating, deflecting, and detecting ions.

Mass Spectrum

Graph produced by a mass spectrometer showing ion abundance versus mass-to-charge ratio (m/z).

Mass-to-Charge Ratio (m/z)

Value obtained in mass spectrometry equal to the ion’s mass divided by its charge; determines deflection amount.

Ionisation (in Mass Spectrometry)

Stage where high-energy electrons remove electrons from sample atoms, producing positive ions (X → X⁺ + e⁻).

Acceleration (in Mass Spectrometry)

Stage where an electric field speeds up positive ions so they can be separated by mass/charge differences.

Deflection (in Mass Spectrometry)

Stage where a magnetic field bends ion paths; lighter or more highly charged ions are deflected more.

Detection (in Mass Spectrometry)

Stage where ions strike a detector, generating signals proportional to their abundance at each m/z value.

Weighted Mean

Average that takes into account both the value (e.g., isotopic mass) and its percentage abundance.

Periodic Table

Arrangement of elements in order of increasing atomic number; shows chemical patterns and relative atomic masses.

Nucleus

Central region of an atom containing protons and neutrons; accounts for nearly all atomic mass.

Shell (Energy Level)

Region around the nucleus where electrons are likely to be found; determines chemical behavior.

Carbon-12 Standard

International reference isotope assigned a mass of exactly 12 u, forming the basis for all relative atomic masses.