Write scientific reasons:
a. Atomic radius goes on decreasing while going from left to right in a period.
  1. As we move from left to right in a period, the atomic number goes on increasing. i.e. the number of electrons goes on increasing along with the number of protons.
  2. Due to this increased nuclear charge, the shells are pulled towards the nucleus with a greater force.
  3. As a result, the atomic radius goes on decreasing while going from left to right in a period.
2 Marks
b. Metallic character goes on decreasing while going from left to right in a period.
  1. Metals show tendency to lose electrons.
  2. As we move from left to right in a period, electrons are successively added in the same shell.
  3. Thus, they experience a greater pull from the nucleus and the release of electrons becomes difficult.
  4. Hence, metallic character goes on decreasing while going from left to right in a period.
2 Marks
c. Atomic radius goes on increasing down a group.
  1. As we move down in a group, number of shells successively goes on increasing.
  2. This naturally increases the radius of the atom.
  3. Atomic size is determined by atomic radius.
  4. Therefore, atomic radius goes on increasing down a group.
2 Marks
d. Elements belonging to the same group have the same valency.
  1. The valency of an element is determined by the number of valence electrons present in the outermost shell of an atom.
  2. Elements belonging to the same group have same number of valence electrons.
  3. Therefore, elements belonging to the same group have the same valency.
2 Marks
e. The third period contains only eight elements even through the electron capacity of the third shell is 18.
  1. Electrons are filled in shells according to the octet rule.
  2. According to this rule, the outermost shell can contain a maximum of 8 electrons.
  3. Therefore, the third period contains only eight elements even through the electron capacity of the third shell is 18.
2 Marks

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30 July 2019 at 03:18