Unit 1 – Atomic Structure & Nuclear Chemistry Vocabulary

Vocabulary flashcards covering the essential terms and definitions related to atomic structure, isotopes, ions, average atomic mass, and nuclear chemistry concepts discussed in the lecture notes.

Atom

The smallest unit of an element that retains the chemical properties of that element.

Subatomic Particle

Particles that make up an atom—protons, neutrons, and electrons.

Proton (p⁺)

Positively charged subatomic particle located in the nucleus; mass ≈ 1 amu; determines atomic number and element identity.

Neutron (n⁰)

Neutral subatomic particle located in the nucleus; mass ≈ 1 amu; number can vary to create isotopes.

Electron (e⁻)

Negatively charged subatomic particle found in orbitals around the nucleus; mass ≈ 0.0005 amu.

Atomic Number (Z)

Number of protons in an atom’s nucleus; identifies the element.

Mass Number (A)

Total number of protons plus neutrons in an atom’s nucleus.

Isotope

Atoms of the same element (same Z) that differ in mass number due to different numbers of neutrons.

Ion

Charged atom or group of atoms formed by gaining or losing electrons.

Cation

Positively charged ion formed when an atom loses one or more electrons; typical of metals.

Anion

Negatively charged ion formed when an atom gains one or more electrons; typical of non-metals.

Neutral Atom

Atom with equal numbers of protons and electrons, resulting in zero net charge.

Average Atomic Mass

Weighted average mass of the naturally occurring isotopes of an element, expressed in amu.

Percent Abundance

The percentage of each isotope present in a natural sample of an element.

Mass Spectroscopy

Analytical technique that measures isotope masses and relative abundances to determine average atomic mass.

Chemical Reaction

Process involving rearrangement of valence electrons; atoms keep their identities; relatively small energy changes.

Nuclear Reaction

Process that changes the nucleus of an atom, potentially transmuting elements; involves large energy changes; unaffected by temperature or pressure.

Fission

Nuclear process in which a heavy nucleus splits into two lighter nuclei, releasing large amounts of energy.

Fusion

Nuclear process in which two light nuclei combine to form a heavier, more stable nucleus, releasing even more energy than fission.

Chain Reaction

Self-sustaining fission process in which released neutrons trigger further fission events.

Alpha Particle (α)

Helium-4 nucleus (²⁴He) emitted during alpha decay; low penetration power, stopped by paper or skin.

Beta Particle (β)

Fast-moving electron (β⁻) or positron (β⁺) emitted during beta decay; moderate penetration, stopped by metal foil or wood.

Gamma Ray (γ)

High-energy electromagnetic radiation released from an excited nucleus; no mass or charge; high penetration, requires lead or concrete shielding.

Half-Life

Time required for half the nuclei in a radioactive sample to decay.

Law of Conservation of Mass

Principle stating that matter cannot be created or destroyed; total mass of reactants equals total mass of products.

Transmutation

Conversion of one element into another during a nuclear reaction.

Bombardment

Nuclear reaction initiated by striking a nucleus with a particle (e.g., neutron capture).

Capture (nuclear)

Process in which a nucleus absorbs a particle, often leading to radioactivity (e.g., neutron capture).

Emission (nuclear)

Release of a particle or radiation from an unstable nucleus during radioactive decay.

Element Identity

Characteristic determined solely by the number of protons (atomic number) in the nucleus.