Chapter 3: Molecules, Compounds, and Chemical Equations (Vocabulary)

Vocabulary flashcards covering key concepts, terms, and definitions from the lecture notes on molecules, compounds, and chemical equations.

Compound

A substance made of two or more elements in fixed proportions, held together by chemical bonds.

Chemical Bond

An attractive force that holds atoms together in compounds, arising from interactions between electrons and protons.

Ionic Bond

A bond formed by transfer of electrons from a metal to a nonmetal, producing oppositely charged ions.

Covalent Bond

A bond formed when two or more nonmetals share electrons, creating a molecule.

Ionic Compound

A compound composed of cations and anions held together by ionic bonds; in the solid state, it forms a lattice.

Molecular Compound

A compound formed from covalent bonds between nonmetals; units are molecules.

Lattice

A regular three‑dimensional arrangement of ions in a crystalline solid.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Empirical Formula

The simplest whole‑number ratio of atoms in a compound; may differ from the actual molecule’s composition.

Molecular Formula

The actual number of each type of atom in a molecule.

Structural Formula

A representation using lines to show how atoms are connected and, sometimes, the molecule’s geometry.

Formula Unit

The lowest whole‑number ratio of ions in an ionic compound.

Type I Ionic Compound

An ionic compound in which the metal forms only one type of cation across compounds.

Type II Ionic Compound

An ionic compound in which the metal can form more than one cation; the charge is shown with Roman numerals.

Polyatomic Ion

A charged species composed of two or more atoms covalently bonded.

Oxyanion

A polyatomic ion that contains oxygen.

Hydrate

An ionic compound that has a specific number of water molecules per formula unit.

Hydrate Prefixes

Prefixes (mono-, di-, tri-, tetra-, etc.) indicating the number of water molecules; hemi means 1/2.

Binary Ionic Compound

Compound formed from a metal and a nonmetal (two elements).

Binary Molecular Compound

Molecular compound formed from two nonmetals.

Prefixes (mono-, di-, tri-, etc)

Prefixes used in molecular naming to indicate the number of atoms; mono is often omitted for the first element.

Diatomic Elements

Elements that exist naturally as diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2 (P4 and S8 are polyatomic elements).

Atomic Element

An element that exists in nature as single atoms.

Molecular Element

An element that exists as molecules (diatomic or polyatomic) rather than as single atoms.

Acid

A molecular compound that releases H+ ions when dissolved in water; binary acids contain hydrogen and a nonmetal, oxyacids contain hydrogen and a polyatomic anion.

Binary Acids

Acids with hydrogen and a nonmetal; named with the hydro- prefix and -ic suffix (e.g., HF = hydrofluoric acid).

Oxyacids

Acids containing hydrogen and a polyatomic anion; names change -ate to -ic and -ite to -ous, then add 'acid'.

Mass Percent Composition

The mass percentage of an element in a compound: (mass of element in 1 mol of compound / molar mass) × 100%.

Formula Mass

The sum of the atomic masses of all atoms in a formula unit or molecule (amu). Also called molecular mass.

Molar Mass

Mass, in grams, of 1 mole of a substance; numerically equal to the formula mass in g/mol.

Empirical Formula from Percent Composition

Process: convert percents to grams, convert to moles, form a pseudoformula, divide by the smallest mole, and scale to whole numbers.

Combustion Analysis

Burning a known mass of a compound in oxygen to weigh CO2 and H2O, determining elemental composition and empirical formula.

Molecular Formula from Empirical Formula and Molar Mass

If you know the empirical formula and the molar mass, multiply the empirical formula by an integer n so that n × (empirical formula mass) equals the molar mass.

Alkanes

Hydrocarbons with only single bonds between carbon atoms.

Alkenes

Hydrocarbons with at least one carbon–carbon double bond.

Alkynes

Hydrocarbons with at least one carbon–carbon triple bond.

Functional Group

A specific group of atoms that imparts characteristic chemical behavior to a family of organic compounds.

Alcohols

Organic compounds with the -ol ending and an -OH group (R–OH).

Ethers

Organic compounds with the -ether group (R–O–R').

Aldehydes

Organic compounds with the -al ending and the form R–CHO.

Ketones

Organic compounds with the -one ending and the carbonyl group R–CO–R'.

Carboxylic Acids

Organic acids with the -oic acid ending (R–COOH).

Esters

Organics with the -ate ending and the group R–COOR'.

Amines

Organic compounds with the -amine ending (R–NH2).

Ball‑and‑Stick Model

A molecular model with balls as atoms and sticks as bonds to show connectivity and shape.

Space‑Filling Model

A molecular model where atoms are scaled to reflect occupied space, illustrating molecular surface.

Mole

The amount of substance containing exactly 6.022 × 10^23 entities; a base unit for chemical quantities.

Avogadro’s Number

6.022 × 10^23, the number of entities in one mole.