Chemistry - formulae and equations

Element

An element is a substance made up of only one type of atom.

Compound

A compound is made up of at least two different elements chemically bonded together. This means compounds are made up of more than one type of atom.

Nitrate Ion

Nitrate: NO3-

Carbonate Ion

Carbonate: CO3 2-

Oxide Ion

Oxide: O2-

Hydroxide Ion

Hydroxide: OH-

Ammonium Ion

Ammonium: NH4+

Sulfate Ion

Sulfate: SO4 2-

Ionic Compound

Ionic compounds are made up of positive and negative ions, held together by electrostatic attraction.

Sodium Chloride Formula

Sodium chloride has the formula NaCl as the charges on the ions must cancel to give a compound with no overall charge.

Aluminium Oxide Formula

For the ionic compound to have no overall charge, two aluminium ions must bond with three oxygen ions, giving the formula Al2O3.

Zinc Nitrate Formula

For the ionic compound to have no overall charge, two nitrate ions must bond with the zinc ion. This gives the formula Zn(NO3)2.

Oxidation Number

A number assigned to an atom or an ion which represents how many electrons have been lost or gained by the atom.

Oxidation Number of an Element

Zero.

Overall Oxidation Number of CaCO3

Zero. The oxidation numbers of a neutral compound add up to zero.

Overall Oxidation Number of HCO3-

-1. The overall oxidation number of a charged compound is simple as it is the charge shown on the molecule.

Oxidation States of Hydrogen and Oxygen

Hydrogen: +1 (except in metal hydrides where it is -1). Oxygen: -2 (except in peroxides and F2O where it is -1).

Common Oxidation States of Halogens and Group One Metals

Halogens: -1. Group one metals: +1.

Oxidation Number of Sulfur in Na2SO4

Sulfur must have an oxidation number of +6 to balance the charges.

Oxidation Number of Chromium in K2Cr2O7

Chromium must have an oxidation number of +6 to balance the charges.

State Symbols in Chemical Equations

(g) - gas; (aq) - aqueous; (l) - liquid; (s) - solid.

Ionic Equation

Ionic equations only show the reacting ions and can be written for any reaction involving ions in solution.

Ionic Equation for HNO3 and NaOH

H+(aq) + OH-(aq) → H2O(l)

Ionic Equation for AgNO3 and NaCl

Ag+(aq) + Cl-(aq) → AgCl(s)