Innumerable chemical reactions occur in the world around us. They all obey the authority of electron-shell chemistry. An atom may gain electrons or may lose them, becoming a negatively or a positively charged ion. An atom can combine with hundreds and thousands of others to form a giant molecule. But it always remains the carrier of the properties of the same element. Carbon forms over three million compounds, but in each of them, be it carbon dioxide CO₂ or the most complicated antibiotic, carbon remains carbon.

   Changing an element into another involves rearranging its atomic nuclei to alter their charge.

   To bring about chemical processes chemists make use of high temperatures and pressures and of catalysts, substances which accelerate reactions when added in small amounts. Temperatures of thousands of degrees and pressures of hundreds of thousands of atmospheres fail to rearrange the atomic nucleus. One element cannot be changed into another in this way.

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