Chemistry 1A: Atoms, Molecules, Ions, and Compounds

Vocabulary practice flashcards covering fundamental chemistry concepts from Chapters 2 and 3, including early atomic theory, nuclear structure, subatomic particles, isotopes, mass spectrometry, the periodic table, the mole concept, ionic and covalent bonding, nomenclature, and chemical formulas.

Atomos

The Greek term meaning uncuttable or indivisible, proposed by Democritus to describe matter divided to its smallest unit; an idea repressed for approximately 2,000 years due to opposition from Aristotle.

Law of Conservation of Matter

The scientific principle stating that there is no detectable change in the total quantity of matter present when matter converts from one type to another during physical or chemical changes.

Law of Definite Proportions

The law stating that regardless of its source, a particular compound is always composed of the same elements in the exact same proportions or parts by mass.

Dalton's Atomic Theory

A five-postulate atomic framework proposing that matter consists of indivisible atoms, elements contain identical characteristic atoms, atoms differ across elements, compounds combine atoms in small whole-number ratios, and chemical reactions simply rearrange atoms without creating or destroying them.

Cathode Ray

A visible stream of negatively charged particles emitted across electrodes in an evacuated glass tube under high voltage, which J.J. Thomson used to discover the electron and calculate its charge-to-mass ratio ($1.759 \times 10^{11}\,\text{C/kg}$).

Electron

A negatively charged subatomic particle located outside the nucleus with a mass of approximately $0.00055\,\text{amu}$ ($9.107 \times 10^{-31}\,\text{kg}$) and a fundamental relative charge of $-1$ ($-1.602 \times 10^{-19}\,\text{C}$).

Millikan's Oil Drop Experiment

A 1909 experiment by Robert A. Millikan that manipulated electrically charged microscopic oil droplets in an electric field to establish that the charge on a single electron is $1.6 \times 10^{-19}\,\text{C}$.

Plum Pudding Model

An early atomic model proposed by J.J. Thomson depicting the atom as a positively charged sphere embedded with negatively charged electrons, comparable to raisins distributed in an English dessert.

Rutherford's Gold Foil Scattering Experiment

An experiment directing positively charged alpha ($\alpha$) particles at thin gold foil, demonstrating that atoms are mostly empty space because most particles pass straight through, while a small fraction deflect sharply from a tiny, dense core.

Nucleus

The small, dense, positively charged center of an atom discovered by Ernest Rutherford that contains virtually all of the atom's mass and is composed of protons and neutrons.

Proton

A positively charged subatomic particle found in the nucleus of an atom, possessing a mass of $1.0073\,\text{amu}$ and a relative charge of $+1$.

Neutron

An electrically neutral subatomic particle located in the atomic nucleus, discovered by James Chadwick, with a mass of $1.0087\,\text{amu}$ and a charge of $0$.

Atomic Number ($Z$)

The number of protons in the nucleus of an atom, serving as the defining characteristic that determines an element's chemical identity and also indicating the number of electrons in a neutral atom.

Mass Number ($A$)

The total sum of protons and neutrons present within the nucleus of an atom ($A = Z + \text{neutrons}$).

Atomic Mass Unit (amu)

A small mass unit defined relative to a carbon-12 atom (which equals exactly $12\,\text{amu}$), where $1\,\text{amu} = 1.6605 \times 10^{-24}\,\text{g}$.

Isotopes

Atoms belonging to the same element that contain identical numbers of protons but differing numbers of neutrons, resulting in different mass numbers.

Mass Spectrometer

An analytical instrument that vaporizes a sample, ionizes it with an electron beam, and separates the resulting cations using a magnetic field based on their mass-to-charge ratios to determine isotopic abundances.

Periodic Law

The organizational chemical principle stating that the physical and chemical properties of the elements recur periodically when arranged in order of increasing atomic number.

Periods

The horizontal rows of elements in the periodic table along which atomic numbers increase sequentially.

Groups

The numbered vertical columns (1 through 18) of the periodic table containing elements that share similar valence configurations and chemical properties.

Avogadro's Number ($N_A$)

The fundamental constant equal to $6.022 \times 10^{23}\,\text{entities/mol}$, representing the number of specified items (such as atoms or molecules) present in one mole of a substance.

Molar Mass

The mass in grams of one mole ($6.022 \times 10^{23}$ entities) of a substance, which is numerically equivalent to the atomic, molecular, or formula mass in atomic mass units ($\text{amu}$).

Ionic Bond

The electrostatic attraction holding oppositely charged ions together in a rigid, three-dimensional extended crystal lattice, formed when electrons are transferred from a metal to a nonmetal.

Covalent Bond

A chemical bond formed between nonmetal atoms through the mutual sharing of valence electrons, resulting in discrete, electrically neutral molecules.

Cation

A positively charged ion formed when a neutral atom (typically a metal) loses one or more valence electrons.

Anion

A negatively charged ion formed when a neutral atom (typically a nonmetal) gains one or more valence electrons.

Polyatomic Ion

A discrete, electrically charged molecule consisting of two or more covalently bonded atoms that carries an overall net electric charge.

Oxyanion

A polyatomic anion composed of a central nonmetal atom covalently bonded to one or more oxygen atoms, such as carbonate ($\text{CO}_3^{2-}$) or sulfate ($\text{SO}_4^{2-}$).

Binary Acid

An aqueous acid containing hydrogen and only one other nonmetallic element, named by applying the prefix hydro-, the root of the nonmetal with the suffix -ic, and the word acid.

Oxyacid

A compound containing hydrogen, oxygen, and at least one other element that exhibits acidic properties, named from the parent oxyanion by changing -ate to -ic acid or -ite to -ous acid without using the prefix hydro-.

Hydrate

A crystalline compound (often ionic) containing a specific stoichiometric ratio of water molecules bound within its solid lattice, represented with a centered dot such as in $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$.

Molecular Formula

A chemical representation showing the exact identities and actual numbers of each type of atom that constitute a discrete molecule of a compound.

Empirical Formula

The simplest chemical formula of a compound showing the lowest whole-number ratio of the constituent elements rather than the actual number of atoms in a molecule.

Formula Mass

The sum of the average atomic masses of all atoms indicated in the empirical chemical formula of an ionic compound or network solid, expressed in atomic mass units ($\text{amu}$).