Chemistry Review: The Mole and Formulas

Vocabulary practice flashcards covering the mole, molar mass, empirical and molecular formulas, percent composition, and gas stoichiometry at STP.

Mole

A counting unit representing $6.02 \times 10^{23}$ particles (atoms, molecules, or formula units) of a substance.

Molar Mass

The sum of the atomic masses of the elements in any compound, representing the mass in grams of one mole of that substance.

Empirical Formula

The chemical formula representing the simplest whole-number ratio of the elements in a compound, which can be determined from percent composition or elemental masses.

Molecular Formula

The chemical formula that gives the actual number of atoms of each element present in a molecule of a compound (for example, $P_4O_{10}$ compared to its empirical formula $P_2O_5$).

Percent Composition

The percentage by mass of each individual element contained in a compound.

Molar Volume at STP

The volume occupied by one mole of any ideal gas at standard temperature and pressure, equal to approximately $22.4\,dm^3$ ($22.4\text{ liters}$).

Diatomic Molecule

A molecule that naturally consists of two bonded atoms of the same element, such as chlorine ($Cl_2$), hydrogen ($H_2$), or oxygen ($O_2$).

Formula Mass

The sum of the atomic masses of all atoms present in a formula unit of an ionic compound (such as $Ba(NO_3)_2$), typically expressed in atomic mass units (amu).

Avogadro's Number

The number of representative particles contained in one mole of any pure substance, equal to $6.02 \times 10^{23}$.

Gas Volume Variables

The three physical conditions that dictate the volume occupied by a gas: pressure, temperature, and number of molecules (independent of the chemical identity of the gas).