Nomenclature & Formula Writing Review

Why do elements bond together? Elements react with each other so that they may have a full outer shell of electrons. They will ‘share’ or ‘steal’ electrons from each other in order to achieve this. Noble gasses already have full outer shell, and this is why they do not tend to react with other elements!

Simple Chemical Formulae Each element has a combining capacity which explains how many available bonding spaces it has. This is linked to the number of valence (outer orbital) electrons the element has. When 2 elements combine, every bonding space must be used.

The criss-cross method: Example: lithium and oxygen What are the combining capacities? Lithium: 1 Oxygen: 2

Because the “1” is implied, we simply write the formula as Li2O.

When possible, the formula must be reduced by its lowest common denominator. Example: magnesium and oxygen

Try these! Sodium and bromine Boron and oxygen Calcium and iodine Magnesium and sulphur NaBr B2O3 CaI2 MgS

Nomenclature (naming of molecules) You should be familiar with four basic naming rules from your previous years.

A. Metal-Nonmetal Write the name of the metal first The name of the nonmetal is written second, with the ending of the name changed to –ide Example: Li2O Lithium oxide

B. Nonmetal-Nonmetal Write the names of the nonmetals in the order that you find them (left to right) on the periodic table. Change the ending of the last one to –ide Use prefixes to indicate how many of each element is present **The nonmetals are rebels! They do not always follow the criss-cross rule you just reviewed. Fortunately, you can determine the formula from the name.

Mono- **generally not used for the first element Di- Tri- Tetra- Penta- Hexa- Hepta- Octa- Nona- Deca-

Example: P5Cl2 Pentaphosphorous dichloride

Your turn… CO Si4O2 NI3 Carbon monoxide Tetrasilicon dioxide Nitrogen triiodide

C. Multivalent metals These metals are found in the transition elements area (middle of the periodic table) Some transition metals have more than one possible combining capacity. For example, copper can have a combining capacity of either 2 or 1. Roman numerals are used in the name to indicate which ion is being used.

Example: copper (I) chloride & copper (II) chloride

***You need to reverse this process to convert from the formula to the name! This is nickel (II) nitride.

Your turn again! Cobalt (II) selenide Tin (IV) bromide NiS Fe2O3 CoS SnBr4 Nickel (II) sulphide Iron (III) oxide

D. Polyatomic Ions Your beloved data table contains a list of common ions and their charges. For naming and formula purposes, treat the ions as a single unit, and follow the criss-cross rule as you have already been doing.

Hints: You will be able to recognize polyatomic names because they are the only ones which do not end in –IDE!! You will be able to recognize polyatomic formulae because they are the only ones with three or more elements. (Of course, this will change as the year goes on….) 

Example: Calcium permanganate

Final round for you to try!!! Sodium phosphate Strontium chlorate NH4Cl CaC2O4 Na3PO4 Sr(ClO3)2 Ammonium chloride Calcium oxalate