Define atomic size. Give its unit of measurement. In the modern periodic table what trend is observed in the atomic radius in a group and a period and why is it so?



  • Atomic size or atomic radius is the distance from the center of the nucleus to the outermost shell of the atom.
  • Atomic size is measured in Angstroms . 1 A o =10 -10


  • In a group, as we move down, the atomic radius increases as the number of energy shells of the atoms keeps on increasing from top to bottom.
  • In a period, as we move from left to right, the atomic radius decreases as the nuclear charge increases but the number of shells increases so this tends to pull the electrons closer to the nucleus. 

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CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo