Atoms and Atomic Theory

A set of vocabulary flashcards covering key concepts related to atoms and atomic theory.

Atom

The basic unit of a chemical element, made up of protons, neutrons, and electrons.

Atomic Theory

The scientific theory that matter is composed of discrete units called atoms.

Subatomic Particles

Particles that are smaller than atoms, including protons, neutrons, and electrons.

Proton

A positively charged subatomic particle found in the nucleus of an atom.

Neutron

A subatomic particle found in the nucleus of an atom that has no charge.

Electron

A negatively charged subatomic particle that orbits the nucleus of an atom.

Nucleus

The central region of an atom, containing protons and neutrons.

Dalton's Atomic Theory

The theory stating that all matter is made up of atoms, which are indivisible and unique to each element.

Isotope

Variants of a particular chemical element that have the same number of protons but different numbers of neutrons.

Atomic Number

The number of protons in the nucleus of an atom, which determines the element's identity.

Mass Number

The total number of protons and neutrons in the nucleus of an atom.

Unified Atomic Mass Unit

A standard unit of mass that describes the mass of an atom or molecule; is exactly 1/12 the mass of a carbon atom with mass number 12.

Mole

The SI base unit used to measure the amount of substance, representing 6.022 x 10^23 particles.

Electron Configuration

The distribution of electrons in an atom's energy levels and orbitals.

Ground State

The lowest energy state of an atom's electrons.

Excited State

When an electron has absorbed energy and moved to a higher energy level.

Photon

A unit or quantum of light or other electromagnetic radiation.

Orbital

A region in an atom where there is a high probability of finding electrons.

Valence Electron

An electron found in the outermost shell of an atom that determines the atom's chemical properties.

Plum-Pudding Model

Thomson's model of the atom, proposing that electrons are distributed within a positively charged 'soup' within the atom.

Gold-Foil Experiment

An experiment conducted by Rutherford that led to the discovery of the nucleus.

Law of Definite Proportions

A chemical compound always contains the same elements in exactly the same proportions by weight or mass.

Radioisotope

An unstable isotope that emits radiation and decays into other isotopes.

Energy Level

The fixed distance from the nucleus of an atom where electrons can orbit.

Avogadro's Number

The number of atoms or molecules in one mole of a substance, approximately 6.022 x 10^23.