Honors Chemistry: Atoms - The Building Blocks of Matter and Nuclear Science

Vocabulary flashcards covering the structure of the atom, historical atomic models, subatomic particles, isotopes, and nuclear chemistry concepts from Chapters 3 and 21.

Democritus

The ancient Greek natural philosopher who first proposed the notion of the atom.

Atom (Etymology)

Derived from a Greek root meaning "indivisible."

Atom

The smallest unit of an element that can exist either alone or in molecules, retaining the chemical properties of that element.

Neutral Atom

An atom that contains equal numbers of positively charged protons and negatively charged electrons.

Law of Conservation of Mass

A fundamental principle stating that mass cannot be created or destroyed; in a chemical reaction, the total mass of the products equals the sum of the masses of the reactants.

Dalton's Atomic Theory

An atomic model stating that all matter is composed of indestructible atoms, atoms of an element are identical, atoms combine in simple whole-number ratios to form compounds, and chemical reactions involve the combination, separation, or rearrangement of atoms.

Modifications to Dalton's Atomic Theory

Two statements later revised by modern atomic theory: (1) atoms can be divided into subatomic particles, and (2) not all atoms of the same element are identical (isotopes have different numbers of neutrons).

Cathode-Ray Tube Experiment

Experiments with gas-filled glass tubes at low pressure demonstrating that cathode rays are composed of negatively charged particles (electrons) found in all atoms.

Rutherford's Gold-Foil Experiment

An experiment bombarding thin gold foil with alpha particles, leading to the conclusion that a dense, positively charged region (the nucleus) exists within the atom.

Plum Pudding Model

J.J. Thomson's early atomic model proposed prior to Rutherford's gold-foil experiment, which conceived negatively charged electrons embedded within a uniform sphere of positive charge.

Nuclear Model

Rutherford's atomic model established after the gold-foil experiment, featuring a small, dense, positively charged nucleus surrounded by mostly empty space containing electrons.

Proton

A positively charged subatomic particle found in the nucleus with a relative charge of $+1$ and significant mass.

Neutron

A subatomic particle located in the nucleus having no electrical charge ($0$) and a mass approximately equal to that of a proton.

Electron

The least massive subatomic particle in an atom, carrying a charge of $-1$ and occupying most of the atom's volume outside the nucleus.

Atomic Number

The number of protons in the nucleus of an atom, identifying the element.

Mass Number

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

Isotopes

Atoms of the same element that have the same atomic number but different mass numbers due to differing numbers of neutrons.

Ion

A charged atom or group of atoms formed when an atom gains or loses electrons, resulting in an unequal number of protons and electrons (such as $\text{Ca}^{2+}$ or $\text{F}^-$).

Average Atomic Mass

The weighted average of the atomic masses of the naturally occurring isotopes of an element based on their percent abundances.

Alpha Radiation

A type of nuclear radiation consisting of the release of a helium nucleus ($2$ protons and $2$ neutrons).

Beta Radiation

A type of nuclear radiation consisting of the release of a high-speed electron.

Gamma Radiation

High-energy nuclear radiation consisting of photons of light released with no mass or charge.

Nuclear Reaction

A process occurring within the nucleus accompanied by small changes in mass and huge energy changes, during which protons, neutrons, electrons, and gamma rays can be lost or gained.

Radioactive Decay

The spontaneous emission of energy (in the form of alpha, beta, or gamma radiation) that occurs when an unstable nucleus breaks down.

Nuclear Fusion

A nuclear process in which two light nuclei join together to form a single heavier nucleus.

Nuclear Fission

A nuclear process involving the splitting of one heavy nucleus into two or more smaller nuclei, subatomic particles, and energy.

Mass-Energy Equivalence ($E = mc^2$)

The equation stating that mass can be converted into energy and vice versa, describing the direct relationship between mass and huge releases of energy in nuclear reactions.