Important Questions for Class 10 Chapter 5 - Periodic Classification of Elements

Important questions based on NCERT syllabus for Chapter 5 - Periodic Classification of Elements:

Question-1: How will the tendency to gain electrons change as we go from left to right across a period? Why?

Solution: 1. On moving from left to right across a period, metallic character decreases and non-metallic character increases.
2. Since metals tend to lose electrons and non-metals tend to gain electrons, the tendency to gain electrons increases as we move from left to right across a period.

Question-2: How and why does the atomic size vary as you go:

  1. From left to right across a period?
  2. Down a group?

Solution: 1. Atomic size decreases on moving from left to right across a period. This is due to the increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.

  1. Atomic size increases on moving down a group. This is due to addition of new shells which increases the distance between the outermost electrons and the nucleus even though nuclear charge increases.

Question-3: What were the limitations of Newland’s Law of Octaves?

Solution: The limitations of Newland's Law of Octaves are:-

  1. It was not valid for elements beyond calcium.
  2. When new elements like noble gases were discovered, his table had no place for them.
  3. Placing of iron far away from cobalt and nickel, which have similar properties as iron, could also not be explained.