Size of atoms

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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.













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