Chapter 4: Atomic Structure

Vocabulary practice flashcards covering early atomic theory, key discoveries of subatomic particles, experimental apparatus, and atomic structure fundamentals from Chapter 4.

Democritus

A Greek philosopher who proposed that matter is composed of solid, homogeneous, indestructible, and indivisible atoms that move through empty space, with their size, shape, and movement determining the properties of matter.

Aristotle

A Greek philosopher who asserted that empty space cannot exist and that matter is composed of four elements: earth, fire, air, and water—a view that remained unchallenged for 2,000 years.

Dalton's Atomic Theory

A theory proposed by John Dalton stating that matter is composed of indivisible atoms, atoms of a given element are identical and unique, and chemical reactions involve the combination, separation, or rearrangement of atoms into compounds.

Atom

The smallest particle of an element that retains all the properties of that element.

Cathode-Ray Tube

A glass tube from which most of the air has been removed, through which scientists passed electricity to study radiation and subatomic particles.

Electron

The first subatomic particle discovered, identified by J.J. Thomson in experiments determining its charge-to-mass ratio, earning him the Nobel Prize in 1906.

Plum Pudding Model

An atomic model proposed by J.J. Thomson featuring a spherically shaped atom composed of a uniformly distributed positive charge embedded with negatively charged electrons.

Oil-Drop Experiment

An experiment performed by Robert Millikan in 1910 that determined the charge of an electron to be $1.602 \times 10^{-19}\text{ coulombs}$ and calculated its mass as $9.1 \times 10^{-28}\text{ g}$ ($1/1840$ the mass of a hydrogen atom).

Gold Foil Experiment

An experiment conducted by Ernest Rutherford in which alpha particles were shot at thin gold foil; deflections at large angles led to the discovery of the atomic nucleus.

Nucleus

The tiny, dense region located in the center of an atom that contains all of the atom's positive charge and almost all of its mass.

Proton

A positively charged subatomic particle discovered by Ernest Rutherford located in the nucleus, carrying a charge of $1+$.

Neutron

A neutral subatomic particle discovered by James Chadwick in 1932 that resides in the nucleus, carries no electric charge, and has a mass nearly equal to that of a proton.

Atomic Number

The number of protons in an atom, which uniquely identifies an element and equals the number of electrons in a neutral atom.

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons, resulting in different masses but identical chemical behavior.

Mass Number

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

Atomic Mass Unit (amu)

A unit of mass defined as exactly one-twelfth the mass of a carbon-12 atom.

Atomic Mass

The weighted average mass of the naturally occurring isotopes of an element.