1. (c) The atoms lose their electrons more easily.
2. (b) Mg
3. (a) Neon
4. (a) All the elements in the in the same column as boron have three electrons in the
valence shell. That is all the elements are trivalent.
(b) All the elements in the same column as fluorine has one electron in the valance
shell, which is all the elements, are monovalent.
5. Chlorine has the electronic configuration 2, 8, 7.
(a) Atomic number of element is 17.
(b) F (9)
6. (a) A is a non-metal.
(b) C is less reactive than A.
(c) C will be smaller than B.
(d) A will form anion.
7. Nitrogen atomic number 7 has got 7 electrons with electronic configuration 2, 5.
Phosphorus with atomic number 15 has got 15 electrons with electronic
configuration 2, 8, 5.
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Non-metallic character decreases as we move down the group. Therefore, nitrogen
will be more electronegative than phosphorus.
8. Group number on an element can be predicted from the number of electrons in the
Period number of an element can be predicted from the number of shells with filled
Knowing the electronic configuration, we can find the number of electrons in the
outermost shell and the number of shells with filled electrons. This can help to relate
its position in the Periodic Table.
9. Elements in a group have similar properties. Elements with atomic numbers 12 and
38 lie in the same group as calcium. Therefore, they will have properties resembling
a. In both tables, physical and chemical
properties has been taken basis for
classification and kept in same group.
b. The formulae of the oxide and
hydrides formed by an element were
treated as one of the criteria for
classification of elements.
a. While Mendeleev’s Table was based
on the atomic mass but modern
Periodic table is based on atomic
b. Mendeleev’s Table contain 6periods
and 8 groups but modern periodic
table contain 7 periods and 18
c. Transition elements have been placed
at the end of Mendeleev’s periodic
table but in modern periodic table
they are placed in the middle.