Atoms, Ions, and Molecules – Lesson 4: Chemical Formula

Vocabulary flashcards covering key terms and definitions from Lesson 4 on chemical formulas, including formula types, naming rules for ionic, molecular, acid, base, and hydrate compounds, and essential tools for representing molecular structure.

Chemical Formula

A symbolic representation that shows the elements present in a compound and the number of atoms of each.

Molecular Formula

Formula that gives the actual number of each type of atom in one molecule (e.g., C₆H₁₂O₆).

Empirical Formula

Formula that gives the simplest whole-number ratio of the atoms in a compound (e.g., CH₂O for glucose).

Structural Formula

Diagram that shows how atoms are bonded together using lines for bonds (e.g., H–O–H).

Lewis Structure

Structural formula showing valence electrons as dots; lines represent shared pairs, dots lone pairs.

Ball-and-Stick Model

3-D molecular model emphasizing bond angles and relative positions of atoms with ‘sticks’ for bonds.

Space-Filling Model

3-D model where spheres are scaled to atomic radii, showing the molecule’s overall shape and volume.

Ionic Compound

Compound composed of cations (metals) and anions (non-metals); overall electrically neutral.

Binary Ionic Compound

Ionic compound consisting of only two different elements (e.g., NaCl).

Ternary Ionic Compound

Ionic compound containing more than two elements, usually because of polyatomic ions (e.g., KNO₃).

Cation

Positively charged ion formed by loss of electrons, typically a metal or NH₄⁺.

Anion

Negatively charged ion formed by gain of electrons, often a non-metal or polyatomic species.

Polyatomic Ion

A charged group of covalently bonded atoms that acts as a single ion (e.g., SO₄²⁻).

Stock System

Naming convention using Roman numerals to indicate the oxidation state of a metal that forms more than one cation (e.g., iron(III) oxide).

Crisscross Method

Technique for writing ionic formulas by swapping the ion charges to become subscripts (e.g., Al³⁺ and O²⁻ → Al₂O₃).

Molecular Compound

Compound composed exclusively of non-metals; named with Greek prefixes for atom counts.

Greek Prefixes

mono-1, di-2, tri-3, tetra-4, penta-5, hexa-6, hepta-7, octa-8, nona-9, deca-10; used in molecular names.

Binary Molecular Compound

Two-element molecular compound named with prefixes and –ide ending on the second element (e.g., CO₂ carbon dioxide).

Acid

Substance that yields H⁺ ions in water; formula begins with H.

Simple (Binary) Acid

Acid with H and one non-metal anion; named hydro-…-ic acid (e.g., HCl hydrochloric acid).

Oxoacid

Acid containing H, O, and a central non-metal (e.g., H₂SO₄).

Per-…-ic Acid

Oxoacid with one more O than the –ic acid (e.g., HClO₄ perchloric acid).

…-ous Acid

Oxoacid with one fewer O than the –ic form (e.g., HNO₂ nitrous acid).

Hypo-…-ous Acid

Oxoacid with two fewer O atoms than the –ic form (e.g., HClO hypochlorous acid).

Base

Substance that yields OH⁻ ions in water; named metal hydroxide (e.g., NaOH sodium hydroxide).

Hydrate

Ionic compound that includes a specific number of water molecules in its crystal (e.g., CuSO₄·5H₂O).

Hydrate Naming

Name the salt then add Greek prefix + ‘hydrate’ (e.g., BaCl₂·2H₂O barium chloride dihydrate).

Anhydrous

Term added to a salt’s name when its water of crystallization has been removed.

Transition Metal

Element that can form multiple cations with different charges, requiring Stock notation in names.

Binary Compound

General term for any compound composed of two different elements (ionic or molecular).

Ternary Compound

Compound containing three different elements (commonly involves polyatomic ions).

Nomenclature

Systematic rules chemists use to name chemical substances accurately and unambiguously.

Water of Crystallization

Fixed number of water molecules chemically bound in a hydrate’s crystal lattice.

Functional Group

Specific group of atoms within molecules responsible for characteristic chemical reactions (revealed in structural formulas).