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We frequently define an acid or a base as a substance whose aqueous solution gives, respectively, a higher concentration of hydrogen ion or of hydroxide ion than that furnished by pure water. This is a very one sided definition.

The discovery of various phenomena has led to a recognition of the fact that the chemical atom is an individual which again is itself made up of several units into a selfcontained whole.

Moreover, the abundance of chemical compounds and their importance in daily life hindered the chemist from investigating the question, in what does the individuality of the atoms of different elements consist.

Since hydrogen is a constituent of most of our electrolytic solvents, the definition of an acid or base as a substance which gives up or takes up hydrogen ion would be more general than the one we used before, but it would not be universal.

During the 20th century, we came to understand that the essence of all substances - their colour, texture, hardness and so forth - is set by their structure, on scales far smaller even than a microscope can see. Everything on Earth is made of atoms, which are, especially in living things, combined together in intricate molecular assemblages.

The atoms may be compared to the letters of the alphabet, which can be put together into innumerable ways to form words. So the atoms are combined in equal variety to form what are called molecules.

If you had to sum up chemistry in one sentence, it might be this: Atoms need to have full shells of electrons to feel satisfied, and different elements steal, shed, or borrow different numbers of electrons to achieve a full shell.

Nucleic acids are the main information-carrying molecules of the cell, and, by directing the process of protein synthesis, they determine the inherited characteristics of every living thing. The two main classes of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

The basic parts, the start-up molecules, can be supplied in abundance and don't have to be made by some elaborate process. That immediately makes things simpler.

Chemistry is a class you take in high school or college, where you figure out two plus two is 10, or something.