Shielding Effect (Grade 9 Students) and its trend in Periodic Table.

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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