Chemistry Review: Key Terms from Lecture (Chapter 1–3)

Vocabulary flashcards covering empirical/molecular formulas, molar concepts, measurement principles, and basic chemical nomenclature from the lecture notes.

Empirical formula

The simplest, lowest whole‑number ratio of the elements in a compound, derived from experimental data or percent composition.

Molecular formula

The actual number of atoms of each element in a molecule; may be a multiple of the empirical formula.

Molar mass

Mass of one mole of a substance (g/mol); numerically equal to the formula/molecular weight.

Percent by mass

Mass of an element in a compound divided by the total mass of the compound, times 100.

Elemental analysis

An instrumental method to determine the percent composition of elements in a compound, used to derive empirical formulas.

Isotope

Atoms of the same element that have the same number of protons but different numbers of neutrons.

Atomic number

The number of protons in an atom's nucleus (denoted Z); defines the element.

Mass number

The total number of protons and neutrons in an atom (A).

Atomic mass

The weighted average mass of an element’s isotopes, expressed in atomic mass units (amu).

Avogadro's number

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

Mole

Amount of substance containing Avogadro's number of entities (6.022 × 10^23).

Molar ratio

The ratio of moles of each component in a compound (derived from its formula) used to break it into constituent atoms or ions.

Empirical vs molecular formula

Empirical is the simplest ratio; molecular is the actual formula; they can be the same or different.

Ionic compound

A compound composed of a metal and a nonmetal held together by ionic bonds; named with the metal first and the nonmetal ending in -ide; transition metals may require a roman numeral for charge.

Covalent (molecular) compound

A compound formed between nonmetals, named with prefixes (mono-, di-, tri-, etc.) to indicate the number of atoms.

Diatomic element

Elements that naturally exist as diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2.

Polyatomic ion

An ion composed of two or more atoms bonded together that carries a net charge.

Cation

Positively charged ion; electrons fewer than protons.

Anion

Negatively charged ion; electrons more than protons.

Density

Mass per unit volume (ρ = m/V); used as a conversion factor between mass and volume.

Celsius–Kelvin conversion

Kelvin = Celsius + 273.15; used for temperature calculations in the lab.

Significant figures

Digits that carry meaningful precision in a measurement; rules determine how many figures to retain in calculations.

Accuracy vs. precision

Accuracy is closeness to the true value; precision is repeatability or closeness of multiple measurements to each other.

Period (periodic table)

Horizontal row in the periodic table; properties change across a period.

Group (periodic table)

Vertical column in the periodic table; elements in the same group have similar chemistry.

Isotope notation

Notation showing A (mass number) and Z (atomic number) along with the element symbol; protons = Z, neutrons = A − Z, electrons ≈ Z in a neutral atom.