Chemical reactions and the periodic table

Whenever elements and compounds react together to form a stable compound, the atoms always try to rearrange the outer electrons to achieve a complete outer
electron shell of two or eight. These complete shells were found to be the structures of the elements in group 8 of the periodic table.
The scientists of the nineteenth century discovered new materials that they found to be made up of combinations of simple elements. They began to compare the masses of these elements and discovered that this property was a fundamental characteristic of the element – its atomic mass.
In 1896 a Russian scientist called Mendeleev found that these numerical values could be put into an ordered pattern which he called the periodic table, which was completed later when more elements were discovered. In about 1932 scientists found that the fundamental property that sequenced the elements in their periodic table order was not their mass but the number of protons in their nucleus. This property is called the atomic number, and every element has its own unique atomic number.

In the periodic table according to atomic number all the elements are put in order, each element differing by one unit from its neighbour. It is that simple!
The millions of compounds formed by combining these elements together are not so easily systematized. The use of chemical abbreviations and chemical formulae was introduced as some of the molecules were so huge that using names alone for all their contents would lead to impossibly large words. (see formula and symbols for elements in the Glossary.) There are many millions of compounds made up of approximately 100 different elements. The vast majority of compounds that make up biological tissues are carbon compounds. This branch of chemistry is called organic chemistry. There are over a million compounds containing carbon and hydrogen that are arranged into logical groups based upon what is in them and how they react.
These groups are called ‘homologous series’. Some of these molecules are very large, and proteins are such a group, containing 2000 or more groups of carbon, hydrogen, nitrogen and oxygen atoms. Similarly sugars (or carbohydrates) and fats (lipids) are vast molecules. Of course there are the famous molecules DNA (deoxyribosenucleic acid) and RNA (ribosenucleic acid), which are combinations of smaller groups joined together in their thousands. These molecules are in twisted bundles inside cells, and if they were untwined and strung end to end the molecules in our body would stretch to the sun and back 600 times.
When these protein and other molecules inside our cells are working efficiently then we are well, but if they go wrong, something has to be done. Usually our own body mechanisms can correct these faults itself, but sometimes medication and drugs are needed. That is the beginning of our story about the chemistry of cells and drugs.
Understanding of these complex chemicals needs to be built up in small steps by studying the chemistry of their component parts. Drugs and medicines containing hydrocarbon compounds are covered in Chapter 2; compounds containing OH groups are studied in Chapter 3; the precursors of sugars and fats start with a study of carbonyl compounds in Chapter 4; and the starting point for understanding proteins is the study of amino compounds and amino acids in Chapter 5. Some of the processes involved in the chemistry of medicinal compounds require an understanding of what is meant by covalency, acids, oxidation, solubility, the speed of a reaction and the role of metal ions.