Foundations of Chemistry: Matter, Atomic Theory, and Chemical Laws

Vocabulary practice flashcards covering fundamental chemistry concepts, conservation of mass, atomic theory history, subatomic particles, models of the atom, chemical decomposition, and the law of definite proportions.

Law of Conservation of Mass

The scientific principle stating that in a closed system, the mass of the system cannot change over time; the mass of the reactants must equal the mass of the products, and matter cannot be created or destroyed.

Closed System

A perfectly sealed physical environment where nothing can enter and nothing can escape.

Balanced Chemical Equation

A chemical equation demonstrating that mass is conserved by having an equal number and kind of atoms on both the reactant and product sides.

Skeleton Equation

An unbalanced chemical equation that does not obey the law of conservation of mass because the number and kinds of atoms differ between the reactants and the products.

Coefficient

A number placed directly in front of a chemical species in a chemical equation to modify the number of atoms or molecules present so that the equation obeys mass conservation.

Matter

Any physical substance that takes up space and has mass.

Atom

The fundamental unit of matter, derived from the Greek word atomos, meaning indivisible.

Proton

A subatomic particle located in the atomic nucleus that possesses a positive electrical charge and a mass of $1\,\text{atomic mass unit}$.

Neutron

A subatomic particle located in the atomic nucleus that has a neutral electrical charge and a mass of $1\,\text{atomic mass unit}$.

Electron

A subatomic particle located in the electron cloud that has a negative electrical charge and negligible mass, approximately $0.05\%$ of a proton's mass.

Atomic Nucleus

The very small, dense, and positively charged cluster of protons and neutrons located at the center of an atom.

Atomic Number

The number of protons in an atom's nucleus, which uniquely determines the chemical identity of that atom.

Element

A pure substance composed entirely of a single type of atom that cannot be broken down into simpler substances by ordinary chemical means.

Periodic Table

An organized reference chart of the elements arranged in columns and rows displaying each element's name, symbol, atomic number, and atomic mass.

Democritus

The ancient Greek philosopher who proposed that matter could only be divided until reaching the smallest indivisible particle, which he called the atom.

Aristotle

The ancient Greek philosopher who maintained that matter could be divided infinitely without altering its fundamental properties.

John Dalton

The 19th-century scientist who disproved Aristotle by proposing that matter is composed of indivisible, indestructible atoms that combine in fixed ratios to form compounds.

Cathode Ray Tube

An electronic vacuum device (or electron gun) used by J. J. Thomson that produced a magnetic-deflecting green beam of negatively charged particles, leading to the discovery of the electron.

Plum Pudding Model

J. J. Thomson's early model of the atom in which negatively charged electrons were envisioned as embedded within a surrounding sphere of positive charge.

Alpha Particles

Positively charged particles, physically consisting of helium nuclei, that Ernest Rutherford fired at thin gold foil to probe atomic structure.

Ernest Rutherford

The scientist who discovered the atomic nucleus by demonstrating that alpha particles fired at gold foil were occasionally deflected backward, proving that positive charge is concentrated in a tiny, dense core.

Robert Millikan

The scientist who measured the exact charge of an individual electron using the oil drop experiment by balancing downward gravitational forces against upward electrical forces.

Antoine Lavoisier

The late 18th-century chemist who published Elements of Chemistry (1789), defined elements operationally, disproved phlogiston theory, and established the conservation of mass as an inviolable scientific principle.

Libration

The quantitative experimental practice of measuring the exact mass of chemical samples on a balance before and after reactions.

Phlogiston Theory

A 17th- and 18th-century combustion theory, originally proposed as terra penguis by Johann Becker and renamed by George Stahl, asserting that flammable materials release a fire-matter substance called phlogiston during burning.

Dephlogisticated Air

The historical name given by Joseph Priestley in 1774 to oxygen gas, which phlogiston theory presumed to be devoid of phlogiston.

Bohr Model

The 1913 atomic model formulated by Niels Bohr describing negatively charged electrons orbiting a central positive nucleus in discrete, definite paths like a miniature solar system.

Heisenberg's Uncertainty Principle

The quantum physical principle developed by Werner Heisenberg stating that because electrons possess wave-like behavior, it is impossible to simultaneously measure both their position and momentum.

Orbitals

Three-dimensional regions or electron clouds surrounding the atomic nucleus at various energy levels where electrons are most probably found.

Compound

A substance composed of two or more different elements chemically bonded together that can be broken down into simpler compounds or constituent elements.

Bunsen Burner

A standard laboratory gas burner used as a thermal energy source to induce chemical decompositions and changes.

Electrolysis

A chemical decomposition process that sends an electric current through a compound to overcome the electrical attraction holding its constituent ions or elements together.

Law of Definite Proportions

The chemical principle (also known as Proust's law) stating that any chemical compound always contains a fixed, invariant ratio of elements by mass or weight regardless of sample size or source.

Joseph Proust

The French chemist who demonstrated through experiments from the late 1700s to early 1800s that chemical compounds invariably contain elements in definite, unvarying weight proportions.