Chapter 3 – Ionic Compounds: Key Vocabulary

Vocabulary flashcards summarizing essential terms and definitions from Chapter 3 on ionic compounds, covering ion formation, periodic trends, naming conventions, polyatomic ions, acid-base terminology, and key properties and examples.

Ion

An atom or group of atoms that has gained or lost electrons and carries a net electric charge.

Cation

A positively-charged ion formed when a neutral atom loses one or more electrons.

Anion

A negatively-charged ion produced when a neutral atom gains one or more electrons.

Alkali Metal

Group 1A element (e.g., Na, K) that readily loses its single valence electron to form a +1 cation.

Halogen

Group 7A non-metal (e.g., Cl, Br) that readily gains an electron to form a –1 anion.

Octet Rule

Tendency of main-group atoms to gain, lose, or share electrons until they possess eight valence electrons.

Valence Electron

An electron in the outermost shell (highest n) that participates in bonding.

Ionization Energy (IE)

Energy required to remove an electron from a gaseous atom; low IE favors cation formation.

Electron Affinity (EA)

Energy released when an electron is added to a gaseous atom; high EA favors anion formation.

Type I Cation

Main-group metal cation with only one common charge (e.g., Na⁺, Ca²⁺).

Type II Cation

Metal cation (usually transition metal) that can exist in more than one charge state (e.g., Fe²⁺, Fe³⁺).

Monatomic Ion

An ion consisting of a single atom, such as Cl⁻ or Mg²⁺.

Polyatomic Ion

A charged species composed of two or more covalently bonded atoms acting as a single ion (e.g., SO₄²⁻).

Ionic Bond

Electrostatic attraction between oppositely charged cations and anions in an ionic compound.

Ionic Compound

Neutral compound composed of cations and anions held together by ionic bonds (e.g., NaCl).

Formula Unit

The lowest whole-number ratio of ions in an ionic compound’s formula (e.g., CaF₂ contains one Ca²⁺ and two F⁻).

Crystalline Lattice

Regular, repeating three-dimensional arrangement of ions in an ionic solid.

High Melting Point

Characteristic property of ionic compounds due to strong ionic attractions (e.g., NaCl melts at 801 °C).

Electrical Conductivity (in solution)

Ability of dissolved or molten ionic compounds to conduct electricity via mobile ions.

Solubility (of ionic compounds)

Tendency of an ionic solid to dissolve when ion-water attractions exceed ion-ion attractions.

Transition Metal

d-block element that can form multiple cations by losing s and/or d electrons.

Roman-Numeral Naming

Modern system that shows a Type II metal’s charge in parentheses after the metal name, e.g., iron(III) chloride.

–ous / –ic Endings

Older naming system for Type II cations: –ous for lower charge, –ic for higher charge (ferrous vs. ferric).

Group Number Rule

For main-group elements, cation charge = group number (1A, 2A), anion charge = 8 – group number (5A-7A).

Hydrogen Cation (H⁺)

A bare proton; central to acid behavior in aqueous solution.

Hydroxide Anion (OH⁻)

Polyatomic ion responsible for base behavior in aqueous solution.

Acid

Substance that donates H⁺ (protons) in water, forming hydronium ions.

Base

Substance that provides OH⁻ ions in water.

Hydronium Ion (H₃O⁺)

Water molecule bonded to an extra proton; actual form of H⁺ in aqueous solution.

Monoprotic Acid

Acid that donates one proton per molecule (e.g., HCl).

Diprotic Acid

Acid capable of donating two protons per molecule (e.g., H₂SO₄).

Triprotic Acid

Acid capable of donating three protons per molecule (e.g., H₃PO₄).

Sodium Hydroxide (NaOH)

A strong base that supplies one OH⁻ per formula unit; common laboratory reagent.

Barium Hydroxide [Ba(OH)₂]

Strong base that provides two hydroxide ions per formula unit.

Hydrochloric Acid (HCl)

Monoprotic halogen acid; strong acid commonly used in laboratories.

Sulfuric Acid (H₂SO₄)

Diprotic oxyacid; industrially important strong acid.

Nitric Acid (HNO₃)

Strong oxyacid used in fertilizers and explosives; forms nitrate ion.

Acetic Acid (CH₃COOH)

Weak organic acid; forms acetate ion; main component of vinegar.

Smelling Salts [(NH₄)₂CO₃]

Ammonium carbonate; releases ammonia, used to revive consciousness.

Milk of Magnesia [Mg(OH)₂]

Suspension of magnesium hydroxide; used as an antacid and laxative.

Epsom Salts (MgSO₄)

Magnesium sulfate; employed as a laxative and in bath soaks.

Hydrated Lime [Ca(OH)₂]

Calcium hydroxide; used in mortar, plaster, and water treatment.

Lime (CaO)

Calcium oxide; reacts with water to form Ca(OH)₂, used in cement and soil treatment.

Noble-Gas Configuration

Stable electron arrangement resembling that of the nearest noble gas, often achieved by ion formation.

Electron Configuration

Notation showing the distribution of electrons among orbitals in an atom or ion (e.g., 1s² 2s² 2p⁶).