CHEMISTRY #01 – Atoms & Sub-Atomic Particles

Vocabulary flashcards covering major terms, scientists, and concepts from the lecture on atoms and their sub-atomic particles.

Atom

The smallest unit of an element; composed of sub-atomic particles (protons, neutrons, electrons).

Sub-atomic particle

A collective term for protons, neutrons, and electrons found in atoms.

Nucleus

The small, dense, positively charged center of an atom containing protons and neutrons.

Nucleon

A particle located in the nucleus—either a proton or a neutron.

Proton

Positively charged nucleon discovered by Ernest Rutherford; its count equals the atomic number (Z).

Neutron

Neutral nucleon discovered by James Chadwick; contributes to mass number and isotope identity.

Electron

Negatively charged particle (e⁻) located outside the nucleus in electron clouds; much less massive than nucleons.

Bohr Model

Early atomic model showing electrons in fixed orbits around a central nucleus.

Atomic number (Z)

The number of protons in an atom, defining the element.

Mass number (A)

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

Atomic mass unit (amu or u)

SI-based unit used to express atomic and molecular masses.

Spin (1⁄2)

Intrinsic quantum property of protons, neutrons, and electrons associated with their rotation.

Isotope

Atoms of the same element (same Z) that differ in neutron number and mass number.

Ion

Charged atom formed when electrons are gained or lost; charge written with number before sign (e.g., 2⁺).

Cation

Positively charged ion produced by loss of electrons.

Anion

Negatively charged ion produced by gain of electrons.

Gold foil experiment

Ernest Rutherford’s 1919 experiment that led to discovery of the proton and nuclear structure.

Cathode rays

Streams of electrons investigated by J.J. Thomson, leading to electron discovery (1897).

Charge-to-mass ratio

Quantity measured by J.J. Thomson for electrons using cathode rays.

Oil-drop experiment

Experiment that determined the magnitude of the electronic charge (referenced in notes).