Chemistry Unit 3 – Atomic Structure

Vocabulary flashcards covering the history of atomic models, Dalton's atomic theory, subatomic particles, atomic notation, charges, and atomic mass.

Democritus

The thinker who first suggested the idea of atoms in Ancient Greece.

Atomos

An Ancient Greek word meaning indivisible.

John Dalton

The scientist who proposed that matter is made of tiny particles called atoms, which combine in whole-number ratios and are rearranged in chemical reactions.

J.J. Thomson

The scientist who discovered the electron and proposed the plum pudding atomic model.

Plum pudding model

Thomson's atomic model featuring electrons embedded in a positively charged sphere.

Rutherford

The scientist who discovered the small, dense, positively charged nucleus and proved that atoms are mostly empty space.

Niels Bohr

The scientist who discovered that electrons occupy and move in specific energy levels around the nucleus.

Quantum mechanical model

An atomic model developed by Heisenberg and Schrödinger in which electrons exist in probability clouds around the nucleus.

Proton

A subatomic particle located in the nucleus with a charge of $+1$ (positive) that contributes to atomic mass and determines the identity of the element.

Neutron

A subatomic particle located in the nucleus with a charge of $0$ (neutral) that contributes to atomic mass.

Electron

A subatomic particle located in the electron cloud with a charge of $-1$ (negative).

Nucleus

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

Electron cloud

The region around the nucleus where electrons are located.

Neutral atom

An atom that contains equal numbers of protons and electrons, resulting in a net charge of $0$.

Atomic number

The number of protons in an atom, written in the lower left of the element symbol, which is always a whole number because it counts whole particles.

Mass number

The total number of protons and neutrons in an atom ($\text{Mass number} = \text{protons} + \text{neutrons}$), written in the upper left of the element symbol.

Charge

The difference between protons and electrons ($\text{Charge} = \text{protons} - \text{electrons}$), written in the upper right of the element symbol.

Positive charge

The state of an atom having more protons than electrons due to the loss of electrons (for example, a $+2$ charge means the atom has lost $2$ electrons).

Negative charge

The state of an atom having more electrons than protons due to gaining electrons (for example, a $-1$ charge means the atom has gained $1$ electron).

Atomic mass

A weighted average of naturally occurring isotopes that is usually expressed as a decimal.