Question: What is shielding effect? Give its trends in the periodic table.
Answer.
Shielding Effect
The decrease in force
of attraction between nucleus and
valence electrons due to
presence of inner shell electrons is called shielding effect.
It is also known as
screening effect. It increases with increase in inner shell electrons. For
example, Mg has greater shielding effect than Be. This is because Mg has eight
more inner-shell electrons than Be.
Trend in
Periodic Table
In period
As we move from left to
right in a period, shielding effect remains constant. Reason is that the number
of inner shell electrons remains constant along the period.
In group
As we move from top to bottom in a group, shielding
effect increases. This is due to fact that the number of inner shell increases
and hence, inner shell electrons also increase.
For example, Na has greater shielding effect
than Li because of eight more inner shell electrons than Li.
Example 3.5 Identifying the
element whose atoms have greater shielding effect, using periodic table choose the elements whose atoms you expect to
have greater shielding effect.
(a)
Be or Mg (b) C or
Si 2
Solution:
(a) Mg atoms has greater shielding effect than
Be as Mg is relatively down than Be in IIA group.
(b) Si atoms has greater shielding effect than C as Si is relatively down in IVA group.
xercise 3.5
Self-Assessment
Choose the element whose
atoms you expect to have smaller shielding effect.
(a) F or Cl (b) Li or Na
(c) B or Al
Solution.
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