The Atom: Historical Models, Subatomic Particles, and Valence Structures

Vocabulary flashcards based on lecture notes covering atomic history, subatomic particles, atomic models, isotopes, and valence electrons.

Atom

The smallest particle of an element, which consists mostly of empty space.

Democritus

Greek philosopher who suggested in 400 BC that matter is made up of small, indivisible particles called atoms.

John Dalton

Scientist who studied the nature of matter and proposed an atomic theory based on experimental observations.

Dalton's Atomic Theory

Theory stating that atoms are indivisible spherical particles, atoms of the same element are identical, chemical reactions involve simple whole-number ratios of atoms, and atoms of one element are never changed into atoms of another element during a chemical reaction.

J.J. Thomson

Scientist who studied rays produced in cathode ray tubes and discovered the electron.

William Crookes

Scientist who discovered cathode rays, demonstrating that they carry both mass and charge.

Ernest Rutherford

Scientist who conducted the gold foil experiment with alpha particles, discovering the small, dense, positively charged atomic nucleus.

James Chadwick

Scientist who discovered the neutron.

Bohr Model

Atomic model proposed by Niels Bohr showing electrons orbiting the nucleus in circular paths or concentric energy levels.

Energy Level Maximum Electron Capacity

The maximum number of electrons per Bohr energy level: level 1 holds 2 electrons, level 2 holds 8, level 3 holds 18, and level 4 holds 32.

Mass Number ($A$)

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

Atomic Number ($Z$)

The number of protons in the nucleus of an atom.

Isotope

Atoms of the same element (same atomic number $Z$) that have different numbers of neutrons and therefore different mass numbers ($A$).

Valence Electrons

Electrons located in the outermost energy level of an atom that are involved in chemical bonding.

Lewis Dot Structure

A diagram representing the valence electrons of an atom as dots surrounding the element's chemical symbol.

Octet Rule

Principle stating that atoms gain, lose, or share electrons in order to achieve a stable outer energy level containing 8 valence electrons.