Chemistry

Chemistry connects the composition and structure of chemical substances to their properties and transformations. Its central surprise is that rearranging the same chemical atoms can produce a different substance: molecular hydrogen and molecular oxygen can become water without changing which chemical elements are present. Chemical bonds explain the connections; chemical reactions describe the transformations; stoichiometry makes quantitative predictions from the bookkeeping.

This gives a useful route from an invisible world to measurable quantities. A molecule has a definite composition, such as two hydrogen chemical atoms and one oxygen chemical atom in water. A sample contains an enormous number of such molecules. Counting them through amount of substance, measured in moles, lets the same small-number ratios describe a macroscopic sample. The beauty is that the bookkeeping survives this huge change of scale.

This is a section about Chemistry!

Chemistry is a very important subject about which there is a lot to say.

For example, this sentence. And then another one.

Chemistry is fun. Too hard for precise physics (pre quantum computing, see also quantum chemistry), but not too hard for some maths like social sciences.

And it underpins biology.