(BQ) Part 2 book "Concise inorganic chemistry" has contents: General properties of the elements, coordination compounds, hydrogen and the hydrides, group I-The alkali matals, the chlor-alkali industry, group JI - the alkaline earth elements . | General properties of the elements 6 SIZE OF ATOMS AND ·IONS Size of atoms ' The size of atoms decreases fr()m left to right across a period in the periodic table. For example. on moving from lithium to beryllium one extra positive charge is added to the nucleus, and an extra orbital electron is also added. Increasing the nuclear c:harge results in all of the orbital electrons being pulled closer to the nucleus. In a given period, the alkali metal is the largest atom and the halogen the smallest. When a horizontal period contains ten transition elements the contraction in size is larger, and when in addition there are 14 inner transition eleme11ts in a horizontal period, the contraction in size is even more marked. On descending a group in the periodic table such as that containing lithium. sodium, potassiUm, rubidium and caesium, the sizes of the atoms increase due to the effect of extra shells of electrons being added: this outweighs the effect of increased nuclear charge. Size of ions Metals usually form positive ions. These are formed by removing one or more electrons from the metal atom. Metal ions are smaller than the atoms from which they were formed for two. reasons: 1. The whole of the ·outer shell of electrons is usually ionized, . removed. This is one reason why catfons · are much smaller than the original metal atom. 2. A second factor is the effective nuclear charge. In an atom, the number of positive charges on the nucleus is exactly the same as the number of orbital electrons. When a positive ion is formed; the number of positive charges on the nucleus exceeds the number of orbital electrons, and the effective nuclear charge (which is the ratio of the nun:iber of charges on the nucleus to the number of electrons) is increased. This results in the remaining electrons being more strongly attracted by the nucleus. Thus the electrons are pulled in - further reducing the . Table Covalent radii of the .
