Atoms and things

While some Ancient Greek scientists were suggesting medical solutions to common complaints by mixing together natural products, others were ‘thinking’ and
‘wondering’ what the composition was of materials in general. Democritus in 400 BCE suggested that all materials were made up of small particles he called atoms.
He even invented symbols instead of writing the names for elements. In the Western world it was the school teacher and scientist John Dalton, in 1803, who resurrected the idea of the atom. It took until the 1930s for the structure of the atom to be fully understood. Atoms are so small that about 1 000 000 000 atoms of iron would fit onto the point of a pin.
Atoms are composed of a heavy central nucleus containing positively charged protons, and these are accompanied by varying numbers of the same-sized neutral particles called neutrons.
Rotating in orbits around the nucleus like planets around the sun are negatively charged, very small particles called electrons. The positive charge on the nucleus keeps the negative electrons in place by mutual attraction. The orbits contain only a fixed number of electrons; the inner shell holds a maximum of two and the outer orbits eight electrons or more.
Each element has its own unique number of protons and electrons. This is called its atomic number. Whenever elements react together to form molecules they try to arrange their outermost electrons to obtain this complete electron shell (of either two or eight electrons), either by sharing electrons with another atom (called covalent bonding) or by donation and accepting electrons (called ionic bonding). A more complete explanation of these is given in later chapters.
The naturally occurring hydrogen gas molecules, H2, shares one electron from each hydrogen atom so that each now has a share of two electrons. This is a covalent bond (Figure 1.8). The other method of bonding to get a complete outer electron shell is demonstrated with sodium chloride or common salt. Here the outermost single electron of sodium is completely transferred to the chlorine atom. Sodium loses an electron so it then has a net positive charge, whereas the chlorine gains the electron and so has a net negative charge. These two oppositely charged particles, called ions, attract each other and form a strong ionic bond.
As the years progressed, the methods of analysis become more accurate and precise. Scientists were able to detect very small quantities of materials and the structures were worked out. In modern times chemical analysis is done by very accurate and sophisticated techniques.