Notes on Formulae & Chemical Equations (b)

Vocabulary flashcards covering formula derivation, ionic compounds, state symbols, and equation construction from the notes.

Empirical formula

The simplest whole-number ratio of atoms in a compound, derived from the relative numbers of each element.

Subscript

A number written to the lower-right of an element symbol indicating how many atoms of that element are in the molecule.

Coefficient

A number placed before a chemical formula in a balanced equation that multiplies all atoms in that formula; subscripts are not changed when balancing.

Symbol capitalization rule

Element symbols always start with a capital letter; any second letter (if present) is lowercase.

Ionic compound

A compound composed of positively charged cations and negatively charged anions held together by ionic bonds; the formula balances total charges.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Charge balance

In an ionic compound, the total positive charge equals the total negative charge.

Common ions

Frequently memorized ions and their charges, e.g., Na+, K+, Ca2+, Mg2+, Al3+; Cl−, Br−, O2−, S2−, N3−; OH−, NO3−, SO4^2−, CO3^2−, NH4+.

Sodium chloride

NaCl; formed from Na+ and Cl− (an example of an ionic compound).

Magnesium oxide

MgO; formed from Mg2+ and O2−.

Calcium nitrate

Ca(NO3)2; formed from Ca2+ and NO3−.

State symbol

Notation indicating the phase of a substance: (s) solid, (l) liquid, (g) gas, (aq) aqueous.

Full equation

A chemical equation showing all reactants and products with state symbols; not broken into ions.

Ionic equation

An equation showing the ions present in solution by breaking strong electrolytes into ions; spectator ions may be canceled to give a net ionic equation.

Spectator ion

An ion that appears on both sides of a reaction unchanged and is removed when forming the net ionic equation.

Break into ions

In ionic equations, soluble substances are expressed as their constituent ions.

Cancel spectator ions

Removing ions that appear identically on both sides to obtain the net ionic equation.

Balance atoms (coefficients)

To balance an equation, adjust coefficients (not subscripts) so the number of each type of atom is equal on both sides.

Conservation of mass

The total number of each type of atom is the same on both sides of a balanced equation.

Mole ratio

The ratio of moles of reactants to products dictated by a balanced equation, used to relate amounts in stoichiometry.

Precipitation reaction

A reaction that forms an insoluble solid (precipitate) from ions in solution, e.g., AgCl(s) from Ag+ and Cl−.

Precipitate

The insoluble solid produced in a precipitation reaction.