. Principles of modern biology. Biology. Fig. 4-4. Structure of atoms of atomic numbers 1-20 and 26. The central circle represents the atomic nucleus, the number in the circle showing the net positive charge, , the atomic number; the small black circles rep- resent planetary electrons. These figures are purely diagrammatic and do not pretend to show the actual spatial configuration of the electrons. The atoms whose symbols are printed in heavy type are those of elements generally present in living matter. negatively charged particles, the electrons, also present in the atomic Ener
. Principles of modern biology. Biology. Fig. 4-4. Structure of atoms of atomic numbers 1-20 and 26. The central circle represents the atomic nucleus, the number in the circle showing the net positive charge, , the atomic number; the small black circles rep- resent planetary electrons. These figures are purely diagrammatic and do not pretend to show the actual spatial configuration of the electrons. The atoms whose symbols are printed in heavy type are those of elements generally present in living matter. negatively charged particles, the electrons, also present in the atomic Energetically re- volving around the atomic center, like the planets of the solar system, there is another group of electrons, the planetary electrons. The number of protons and electrons present in the whole configuration differs for each particular kind ol atom (Fig. 4-4). but always the total number of electrons present in a given atom is exactly equal to the number of its protons. In short, each atom, as a whole, is an uncharged body. A knowledge of atomic structure provides an understanding of how various atoms enter into chemical union. One group of the atoms (the electropositive atoms) tends to give up one or more planetary electrons, transferring the elec- trons to the planets of atoms of another group (the electronegative atoms), which have a tend- ency to gain planetary electrons. When such an exchange occurs (Fig. 4-5), the participating atoms tend to cling together, constituting a molecule. The atom that has lost electrons now possesses a positive charge, and this makes it cling to the other atom, which having gained electrons, pos- sesses a negative charge. Such studies also explain 4 Actually the atomic center is composed mainly of neutrons, each formed by the union of one proton with one electron. In fact, the number of free protons present in the atomic center is restricted to the num- ber of planetary electrons in each atom, and this de- termines the atomic number
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