Atoms, Molecules and Ions – Part II (General Chemistry I, Lesson 5)

Flashcards covering key definitions, charge trends, nomenclature rules, and representative examples from Lesson 5 on atoms, molecules, ions, and compound naming.

What is an atom?

The smallest unit of an element that retains the element’s identity; composed of a nucleus (protons + neutrons) surrounded by electrons and is electrically neutral (#p⁺ = #e⁻).

What is a molecule?

Two or more atoms covalently bonded together; overall electrically neutral.

What is an ion?

An electrically charged atom or molecule formed when electrons are lost (cation) or gained (anion).

Define cation.

A positively charged ion produced when an atom loses one or more electrons.

Define anion.

A negatively charged ion produced when an atom gains one or more electrons.

Typical ionic charge of Group 1 (alkali metals).

+1

Typical ionic charge of Group 2 (alkaline-earth metals).

+2

Typical ionic charge of Group 17 (halogens).

–1

Typical ionic charge of Group 16 (oxygen/chalcogen group).

–2

What is a homonuclear molecule?

A molecule made of atoms of the same element (e.g., O₂).

What is a heteronuclear molecule?

A molecule composed of atoms of different elements (e.g., H₂O).

Define diatomic molecule.

A molecule consisting of exactly two atoms (same or different).

Define polyatomic molecule.

A molecule containing three or more atoms.

Give an example of a homonuclear diatomic molecule.

O₂, H₂, N₂, etc.

Give an example of a heteronuclear molecule.

H₂O, CO₂, NH₃, etc.

Greek prefix for one atom in covalent naming.

mono-

Greek prefix for two atoms in covalent naming.

di-

Greek prefix for three atoms in covalent naming.

tri-

When naming covalent compounds, when is the prefix “mono-” omitted?

It is never used on the first element’s name.

Name the compound CO.

Carbon monoxide.

Name the compound SF₄.

Sulfur tetrafluoride.

What happens to the final "a" or "o" in a prefix before an element name beginning with "a" or "o"?

The final vowel is dropped (e.g., tetraoxide → tetroxide).

Common name for H₂O.

Water.

Common name for NH₃.

Ammonia.

Naming rule for monovalent metal cations.

Element name + "ion" (e.g., Na⁺ → sodium ion).

Naming rule for polyvalent metal cations.

Element name + (Roman numeral showing charge) + "ion" (e.g., Fe³⁺ → iron(III) ion).

Classical suffixes for metal cations with two possible charges.

-ous for lower charge, ‑ic for higher charge (e.g., Fe²⁺ ferrous, Fe³⁺ ferric).

Naming rule for monatomic anions.

Root of element + "-ide" + "ion" (e.g., Cl⁻ → chloride ion).

For oxyanions with two forms, how are names assigned?

More O atoms → ‑ate; fewer O atoms → ‑ite (e.g., NO₃⁻ nitrate, NO₂⁻ nitrite).

For oxyanions with four forms, what prefixes are used?

per- (most O) and hypo- (least O) with ‑ate/-ite endings (e.g., ClO₄⁻ perchlorate, ClO⁻ hypochlorite).

Binary ionic compound naming rule.

Name metal first, then non-metal root + "-ide"; include Roman numeral if metal has variable charge.

Give the systematic name for FeCl₃.

Iron(III) chloride.

Ternary ionic compound naming rule.

Name the metal first, then the polyatomic ion; include Roman numeral if metal is variable valence.

Give the systematic name for CaSO₄.

Calcium sulfate.

Binary acid naming rule.

hydro- + root of non-metal + "-ic acid" (used for H + non-metal in aqueous solution).

Name the acid HBr(aq).

Hydrobromic acid.

Oxyacid naming rule based on anion suffix.

-ate anion → ‑ic acid; ‑ite anion → ‑ous acid (e.g., nitrate → nitric acid, nitrite → nitrous acid).

Name the acid HNO₂.

Nitrous acid.

Naming rule for bases composed of metal + OH⁻.

Metal name + "hydroxide" (e.g., KOH → potassium hydroxide).

What is the formula for potassium hydroxide?

KOH.

What method is commonly used to balance charges when writing formulas of ionic compounds?

The criss-cross (cross-multiplication) method.

Write the formula for aluminum oxide.

Al₂O₃.

Which subatomic particle has the smallest mass?

Electron.

Which quantity differs between two isotopes of an element?

Mass number (because of differing numbers of neutrons).

How many protons are in the isotope ²³⁸U?

92 protons.