The third state i.e. gaseous state, as water vapour, though not visible is saturated in the air above the ice (Fig.6.2).
Water can be changed from one state to another by the addition or removal of heat. In the above experiment, air outside the glass is at a higher temperature and it supplies heat to the ice inside the glass, so that the ice melts. Similarly when we boil water, we supply heat to the liquid and it begins to convert into gaseous form.
The most familiar form of water for us is of course, the liquid state.
Physical Features of water
The main features that define water as a compound are:
| Molecular Formula | H2O |
| Nature of bonding | Covalent |
| Molecular mass | 18 |
| Vapour density | 9 |
