Chapter 2 Atoms, Molecules and Stoichiometry - Vocabulary Flashcards

Vocabulary flashcards covering key concepts from Chapter 2: Atoms, Molecules and Stoichiometry.

Relative Atomic Mass (Ar)

The weighted average mass of one atom of an element relative to 1/12 of the mass of a carbon-12 atom; calculated from all isotopes and their abundances; unit is atomic mass unit (A.M.U).

Carbon-12 (C-12)

The reference isotope used as the standard; its mass is exactly 12 amu.

Atomic Mass Unit (A.M.U.)

A unit of mass used to express atomic and molecular weights, defined as 1/12 the mass of a carbon-12 atom.

Isotope

Atoms of the same element that have different numbers of neutrons and thus different masses.

Relative Isotopic Mass

The mass of one atom of a specific isotope relative to 1/12 of a carbon-12 atom.

Abundance

The proportion of a particular isotope present in a sample, usually expressed as a percentage.

Weighted Average (Ar calculation)

The process of calculating Ar by summing each isotope’s mass times its fractional abundance.

Relative Formula Mass (Mr)

The sum of the Ar values of all atoms in a molecule; the mass of one molecule relative to 1/12 of a carbon-12 atom.

Empirical Formula

The simplest whole-number ratio of the elements in a compound.

Molecular Formula

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

Mole

The amount of substance that contains Avogadro’s number (6×10^23) of elementary entities.

Avogadro’s Constant (NA)

6×10^23 entities per mole; the number of particles in one mole of a substance.

Combustion Analysis

A method to determine the composition of organic compounds by burning a known mass in oxygen and weighing CO2 and H2O produced.

Carbon Dioxide (CO2)

Gas produced from burning carbon in oxygen; used to determine carbon content in combustion analysis.

Water (H2O)

Product formed containing hydrogen in combustion analysis; used to determine hydrogen content.

Mass Spectrometer

An instrument that measures the abundance of ions as a function of mass-to-charge ratio (m/e) and is used to determine isotopic composition.

Mass-to-Charge Ratio (m/e)

The ratio of an ion’s mass to its electrical charge, used in mass spectrometry to identify substances.

Gas Volumes at RTp/STP

At room temperature and pressure, 1 mole of any gas occupies about 24 dm3 (at STP, about 22.5 dm3); equal volumes of gases contain the same number of molecules under the same conditions.

Concentration by Mass (g/dm3)

The amount of solute per unit volume of solution, expressed as grams per cubic decimeter.

Concentration by Moles (Molarity, mol/dm3, M)

The amount of solute (in moles) per unit volume of solution (per dm3).

Stoichiometry

The calculation of reactant and product amounts in chemical reactions using mole ratios from balanced equations.