Demonstrate a knowledge of chemical formulae and balanced chemical equations

• including ionic compounds

The Periodic Table of the Elements provides a great deal of information about various elements. During the nineteenth century chemists arranged the then-known elements according to chemical bonding, recognizing that one group (the furthermost right column on the Periodic Table, referred to as the Inert Gases or Noble Gases) tended to occur in elemental form (in other words, not in a molecule with other elements). It was later determined that this group had outer electron shells containing two (as in the case of Helium) or eight (Neon, Xenon, Radon, Krypton, etc.) electrons. As a general rule, for the atoms we are likely to encounter in biological systems, atoms tend to gain or lose their outer electrons to achieve a Noble Gas outer electron shell configuration. The number of electrons that are gained or lost is characteristic for each element, and ultimately determines the number and types of chemical bonds atoms of that element can form.

Ionic bonds are formed when atoms become ions by gaining or losing electrons. Chlorine is in a group of elements having seven electrons in their outer shells. Members of this group tend to gain one electron, acquiring a charge of negative1. Sodium is in another group with elements having one electron in their outer shells. Members of this group tend to lose that outer electron, acquiring a charge of positive1. Oppositely charged ions are attracted to each other, thus Cl^- (the symbolic representation of chlorine) and Na⁺ (the symbol for sodium, using the Greek word natrium) form an ionic bond, becoming the molecule sodium chloride. Ionic bonds generally form between elements in Group I (having one electron in their outer shell) and Group VIIa (having seven electrons in their outer shell).

In the formation of a crystal of sodium chloride, each positively charged sodium ion is surrounded by six negatively charged chloride ions; likewise each negatively charged chloride ion is surrounded by six positively charged sodium ions. The overall effect is electrical neutrality.

The metal is always named first and the root of the nonmetal is followed by the suffix “ide” Ex. BaCl2 is Barium Chloride.

Conversely, the formula can be determined from the name. Ex. For Aluminum Oxide we know that the two atoms involved are Aluminum and Oxygen. To determine the necessary subscripts look at the charges on each atom. From the periodic table Al has a charge of +3 and O has a charge of -2. The smallest number of each atom that can balance the charges is therefore Al2O3