Interactive Chemistry Worksheets for Students |
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Introduction
Compounds are pure substances that are made up of two or more elements that are chemically combined in fixed mass ratios. The elements in the compound are joined together by chemical bonds.
The properties of a compound are unique are greatly differ from the elements that make up the compound.
How do you name compounds?
When compounds are named the name of the second element is changed to an “ide” suffix to indicate that the elements are chemically combined and are not just mixtures. Also by convention the metals are named first. Eg. The reaction of magnesium metal and oxygen produces the compound magnesium oxide. The reaction of iron and sulfur produces the compound iron sulfide.
Naming of Binary Compounds
|
Element 1 |
Element 2 |
Compound ("ide" suffix) |
|
Sodium |
Chlorine |
Sodium chloride |
|
Barium |
Sulfur |
Barium sulfide |
|
Aluminum |
Oxygen |
Aluminum oxide |
|
Magnesium |
Nitrogen |
Magnesium nitride |
|
Potassium |
Fluorine |
Potassium fluoride |
What is a chemical formula?
All compounds have a chemical formula which tell us
- the elements that are present in the compound and
- the ratio of these elements in the compound.
For example
- the chemical formula for water is H2O. This means that there are two parts hydrogen to one part oxygen.
- the chemical formula for salt is NaCl. This means that the ratio of sodium to chlorine parts is 1:1
Ionic or covalent?
Compounds may be divided into two main groups, ionic compounds or covalent compounds.
As a general rule it is helpful to know the following
| Ionic Compounds | Covalent compounds |
|
Made of a metal + non-metal Eg. Sodium chloride, NaCl |
Made of non-metal + non-metal Eg. Water, H2O |
|
Composed of positive and negative ions Eg. Na+ and Cl- Are good electrolytes |
Composed of neutral or unchanged molecules. Eg. H2O Are poor electrolytes |
An electrolyte is a liquid that conducts an electric current. The liquid may be molten or aqueous which means dissolved in water.
Ionic substances are made up of charged particles called ions. eg. Na+ and Cl-
Positive ions are called cations and negative ions anions. A helpful way of remembering cations are positives is that the t in cations looks like a + sign!
The positive sodium ion, Na+ is an example of a cation and the negative chlorine ion, Cl- is an example of anion.
When an ionic compound is dissolved in water the positive and negative ions are surrounded by the water molecules. The symbol aq means aqueous or surrounded by water molecules.
The dissolving of sodium chloride or common table salt, chemical formula NaCl is given by the following chemical equation.
NaCl(s) → Na+(aq) + Cl-(aq)
(s) = solid
(aq) = aqueous
Ionic substances are good electrolytes or conductors of electricity when dissolved in water because the charged ions are able to move in an electric field.
The covalent compound water on the other hand is a relatively poor conductor of electricity. It is made up mostly of neutral water particles which are not affected by an electric field.
Please note that water always contains a small amount of H+ and OH- ions and is able to conduct electricity at high voltages, so always be careful. Only test the conductivity of water at school under the directions of a science teacher. A low voltage power pack will be used.