Atomic Structure and the Nuclear Atom

Vocabulary terms and definitions covering atomic structure, the discovery of the nucleus, and models of the atom based on Chapter 22 of the Physics for Cambridge IGCSE workbook.

Scanning tunneling microscope

An instrument capable of showing individual atoms, such as silicon atoms arranged in groups on a crystal surface.

Solar system model of the atom

An atomic model where negatively charged electrons orbit a central, positively charged nucleus, held by electrostatic attraction while their speed keeps them from falling inward.

Ionization

The process by which a particle becomes electrically charged through losing or gaining electric charge.

Positive ion

An atom that has lost an electron, leaving it with more positive charge than negative charge.

Negative ion

An atom that has gained an electron, resulting in more negative charge than positive charge.

Plum pudding model

A disproved model of the atom that represented it as a sphere of positively charged matter with tiny, negatively charged electrons embedded or dotted throughout.

Alpha particle

A fast-moving particle composed of two protons and two neutrons that is emitted by an atomic nucleus during radioactive decay and has almost $8,000$ times the mass of an electron.

Gold foil

A material beaten so thin that it is only a few atoms thick, used by Hans Herreb and Ernest Marston to scatter alpha particles.

Nucleus

The tiny, dense, positively charged core at the center of an atom where almost all of its mass is concentrated.

Diameter of an atom

The approximate overall size across an atom, measured at about $10^{-10}\,\text{meters}$.

Quantum theory

A mathematical physical theory developed after Rutherford's work that depicts atoms as fuzzy entities rather than collections of hard spheres orbiting one another.