Asked Oct 10, 2019

1. Use the second member of each group from Group IA to Group 7A to show that the number of valence electrons on an atom of the element is the same as its group number.


Expert Answer

Step 1

Periodic table is defined as a tabular display of the chemical elements. In a periodic table, elements are arranged in the increasing order of their atomic number.

In the periodic table of elements, the elements having equal number of valance electrons in their outermost shell are present in groups, whereas in periods, the number of valance electrons in elements increases by 1 from left to right for adjacent elements.

The second member of each group from group 1A to 7A is Na, Mg, Al, Si, P, S, and Cl, respectively.

Step 2

The atomic number of Na is 11. Its electronic configuration is,

Na = 1s22s22p63s1

The outermost shell in the sodium atom is 3rd shell, which contains only 1 electron. Therefore, the number of valance electrons in sodium is 1.

The atomic number of Mg is 12. Its electronic configuration is,

Mg = 1s22s22p63s2

The outermost shell in the magnesium atom is 3rd shell, which contains 2 electrons. Therefore, the number of valance electrons in magnesium is 2.

Step 3

The atomic number of Al is 13. Its electronic configuration is,

Al = 1s22s22p63s23p1

The outermost shell in the aluminium atom is 3rd shell, which contains 3 electrons. Therefore, the number of valance electrons in aluminium is 3.

The atomic number of Si is 14. Its electronic configuration is,


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