Basic Chemistry - Chapter 4: The Atom

Vocabulary practice flashcards covering Section 4.3 (The Atom) of Basic Chemistry (Sixth Edition), including atomic theories, experimental discoveries, subatomic particles, and atomic mass units.

Atom

The smallest particle of an element that retains the characteristics of that element and serves as the building block of matter.

Atomos

The Greek term meaning minute particles, reasoned by Greek philosophers in 500 B.C.E. to be the fundamental constituents of all things.

John Dalton

An English scientist (1766–1844) who proposed an atomic theory in 1808 explaining that atoms are responsible for the combinations of elements found in compounds.

Dalton's Atomic Theory

A foundational scientific theory stating that all matter consists of atoms, all atoms of a given element are identical and differ from other elements, compounds form from consistent combinations of atoms, and chemical reactions involve the rearrangement, separation, or combination of indestructible atoms.

Subatomic Particles

Tiny particles that make up atoms, specifically protons, neutrons, and electrons, discovered through experiments with electricity starting in the late 1880s.

Electrical Charge Interaction

The electrostatic principle stating that two like charges repel each other (two positive charges repel, two negative charges repel) and unlike charges attract each other.

Cathode Rays

Streams of small, negatively charged particles (electrons) discovered by J. J. Thomson in 1897 that travel in a cathode ray tube and deflect toward a positive electrode.

Plum Pudding Model

An atomic model proposed by J. J. Thomson where negatively charged electrons and protons are scattered throughout a positively charged cloud.

Ernest Rutherford

A scientist who worked with J. J. Thomson and developed a nuclear model of the atom in 1911 based on results from gold foil experiments.

Gold Foil Experiment

A 1911 experiment in which positive particles were aimed at thin gold foil; the deflection of a small fraction of particles revealed that atoms have a tiny, dense, positively charged center.

Nucleus

A small, dense region in the center of an atom that carries a positive charge and contains almost all of the atom's mass in the form of protons and neutrons.

Proton

A positively charged subatomic particle ($p$ or $p^+$) located in the nucleus with a charge of $1+$ and an atomic mass of $1.007\,\text{amu}$.

Neutron

An electrically neutral subatomic particle ($n$ or $n^0$) located in the nucleus with a charge of $0$ and an atomic mass of $1.008\,\text{amu}$.

Electron

A negatively charged subatomic particle ($e^-$) located outside the nucleus with a charge of $1-$ and an atomic mass of $0.000\,55\,\text{amu}$.

Atomic Mass Unit (amu)

A mass unit defined as exactly one-twelfth of the mass of a carbon atom containing $6$ protons and $6$ neutrons.

Dalton (Da)

The name used in biological sciences for the atomic mass unit (amu), designated in honor of John Dalton.