From the study of sulfur, I felt it would be interesting to study the other elements, particularly non-metals such as nitrogen, carbon, etc. But the chemistry of these elements (like those of many others) is inextricably linked with the chemistry of air and water, through their ‘biogeochemical’ cycles. They were the original Greek elements, along with earth and fire. Of course, air and water can be studied during the study of the element oxygen, but that will not tell the whole story.
To study air and water is to study the idea of cycles, the way substances pass through the earth; through the lithosphere (where most of the minerals come from), the hydrosphere and the atmosphere, usually by the action of living beings (the biosphere). These cycles, in the present time, have been greatly affected by the action of one species, the human beings. So much so that the scientists have named the epoch Anthropocene, i.e., marked by human activities. Much of this involves the idea of pollution, change that causes harm – where it comes from, what it does and how to control it.
Consider water: It is a topic studied across classes and disciplines. It is essential to life and the study of its properties like boiling range, surface tension, capillarity, adhesion/cohesion and its anomalous density pattern are illustrated by its effect on life. Water, in the biosphere, acts as an environment, medium for reactions, as a solvent and as a reactant. So it would be good to do experiments that illustrate the behaviours. Many of these are apparent in real life examples and can be brought to the attention of the students.
The first interesting fact about water on earth is that there is so much of it. The second is that, on earth, it is the only substance to exist in all three phases, solid, liquid and gas. The water cycle (see picture) is a great way of illustrating this.
The author works with Centre for Learning, Bangalore. She can be reached at firstname.lastname@example.org.