Unit 3 chem

Democritus

Proposed that matter is composed of atoms, which are solid, homogeneous, indestructible, and indivisible.

Atoms

The fundamental particles that make up matter, differing in size, shape, and movement.

Aristotle

Argued against the existence of empty space and atoms, claiming matter is composed of earth, fire, water, and air.

Dalton's Atomic Theory

States that all matter is made of atoms, which are indivisible and combine in whole-number ratios to form compounds.

Conservation of Mass

In chemical reactions, atoms are rearranged but neither created nor destroyed, maintaining mass.

J.J

Discovered the electron using cathode ray tubes and proposed the plum pudding model of the atom.

Robert Millikan

Determined the mass and charge of the electron through the oil-drop experiment.

Ernest Rutherford

Discovered that atoms are mostly empty space and that positive charge and mass are concentrated in the nucleus.

Atomic Number

The number of protons (or electrons) in an atom, which identifies the element.

Isotopes

Atoms with the same number of protons and electrons but different numbers of neutrons.

Mass Number

The total number of protons and neutrons in an atom.

Atomic Mass

The weighted average mass of the isotopes of an element.