Given below are some elements of the modern periodic table: ₄Be, ₉Fe, ₁₄Si, ₁₉K, ₂₀Cai. Select the element that has one electron in the outermost shell and write its electronic configuration.ii. Select two elements that belong to the same group. Give reasons for your answer.iii. Select two elements that belong to the same period. Which one of the two has bigger atomic size?

Academic Chemistry NCERT Class 10

i. ₁₉K has one electron in the outermost shell and its electronic configuration is 2, 8, 8, 1.

ii.₄Be and ₂₀Ca belong to the same group i.e., Group 2.

Electronic configuration:

₄Be – 2, 2

₂₀Ca – 2, 8, 8, 2

₄Be and₂₀Ca have the same number of valence electrons in the outermost shell i.e., 2 so they belong to the same group.

iii.₉F and ₄Be belong to the same period i.e., period 2. Electronic configuration:

₉F - 2, 7

₄Be - 2, 2

₄Be has a bigger atomic size than ₉F because the atomic radius decreases as we move from left to right in a period due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and hence the size of the atom reduces.

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Updated on: 10-Oct-2022

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