Let us examine closely the following sets of compounds and study their properties in terms of their physical state, melting points and boiling points.
Properties of compounds
| Compounds |
State |
Melting Point |
Boiling point |
|
| Sodium chloride |
Solid |
1473.8oF |
2575.4oF |
[Group 1] |
| Potassium bromide |
Solid |
1346oF |
2615oF |
| Calcium iodide |
Solid |
1364oF |
2012oF |
| Carbon tetra chloride |
Liquid |
-73.4oF |
170.6oF |
[Group 2] |
| Ammonia |
Gas |
-172.4oF |
91.4oF |
| Sulphur dioxide |
Gas |
-163.4oF |
50oF |
In group-I, all the compounds are solids at room temperature. They have high melting point and even higher boiling points. The compounds belonging to group-II are either gases or liquids. They have very low melting and boiling points. One may wonder why this great variation exists in the properties of compounds? Examining the constituents of the compounds, we understand that group-I compounds are formed between metals and non-metals, whereas group-II compounds contain only non-metals. Groups of compounds containing both metals and non-metals together are called ionic or electrovalent compounds.
Group-II compounds containing only non-metals are called covalent compounds. Let us discuss the different types of compounds in detail.
