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Periodic Classification of Elements — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10SciencePeriodic Classification of Elements3 Marks
Question
Three elements ‘X’, ‘Y’ and ‘Z’ have atomic numbers 7, 8 and 9 respectively.
  1. State their positions (Croup number and period number both) in the Modern Periodic Table.
  2. Arrange these elements in the decreasing order of their atomic radii.
  3. Write the formula of the compound formed when ‘X’ combines with ‘Z’.
✓

Answer


The electronic configuration of the elements X, Y and Z can be written as: (X - 2, 5) (Y - 2, 6) (Z - 2, 7)
  1. Since all the elements consists two valence shells, therefore all will belong to period $2^{nd}$ Group to which X belongs = 10 + 5 = 15
Group to which Y belongs = 10 + 6 = 16
Group to which Z belongs = 10 + 7 = 17
  1. The elements can be arranged according to the decreasing order of atomic radii as follows: X > Y > Z this is because size of the atom decreases when moving from left to right in a period.
  2. When X combines with Z
Valency of X = 3
Valency of Z = 1
Cross multiplying the valences.

The compound formed is $XZ_3$.

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