Classification of Matter and the Development of Atomic Theory

Vocabulary flashcards covering the classification of matter, key atomic theorists, and fundamental experiments in atomic physics and chemistry.

Matter

Anything that has mass and takes up space.

Pure Substance

A type of matter with a fixed composition and consistent properties, including elements and compounds.

Mixture

A combination of two or more substances that are physically combined.

Element

A pure substance that contains only one type of atom.

Compound

A pure substance made of two or more different elements chemically bonded together in a fixed ratio.

Homogeneous Mixture

A mixture that has a uniform composition throughout, such as salt water where the salt is evenly distributed.

Heterogeneous Mixture

A mixture that has a nonuniform composition with visibly different parts or regions, such as a mixture of sand and water.

Democritus

The ancient thinker who proposed that matter is made of tiny, indivisible particles called atomos.

Aristotle

The philosopher who believed matter was continuous and could be divided indefinitely, supporting the idea that matter consisted of four basic elements: earth, water, air, and fire.

Dalton

The scientist who developed the first modern atomic theory and proposed that matter is made of atoms.

Plum Pudding Model

An atomic model proposed by J. J. Thomson in which electrons were embedded in a positively charged sphere.

Bohr

The scientist who proposed that electrons occupy specific energy levels around the nucleus.

Schrödinger

The scientist who developed the quantum mechanical model of the atom, describing electrons in terms of probability distributions rather than fixed paths.

Cathode

The electrode in a cathode ray tube that produces the stream of electrons.

Anode

The electrode in a cathode ray tube that attracts electrons.

Electron

A subatomic particle discovered by J. J. Thomson with a negative electrical charge and a very small mass compared with the entire atom.

Cathode Ray Tube Experiment

J. J. Thomson's experiment showing that a beam deflected toward a positively charged plate, proving that atoms contain negatively charged particles called electrons.

Alpha Particles

Positively charged particles directed at a thin sheet of gold foil in Rutherford's experiment.

Nucleus

The small, dense, positively charged region at the center of the atom discovered by Rutherford, containing most of the atom's mass along with protons and neutrons.

Gold Foil Experiment

Ernest Rutherford's experiment in which most alpha particles passed straight through foil while a few deflected, proving atoms are mostly empty space with a small, dense, positively charged nucleus.

Beryllium

The element bombarded with alpha particles by Chadwick, producing a penetrating form of radiation used to detect neutrons.

Paraffin Wax

The material at which Chadwick directed radiation from bombarded beryllium, causing protons to be ejected.

Neutron

An electrically neutral particle discovered by James Chadwick, located in the nucleus with approximately the mass of a proton.