Question

Formulas to find the element's group , block and period

Answer 1

a))) PREDICTION of PERIOD
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In the electronic configuration of an atom , the principal quantum number of valance electron represents the PERIOD of the element .
example :- Ca ( atomic no = 20 )
configuration of Ca : 1s², 2s² , 2p^6 , 3s² , 3p^6, 4s² .
valance electrons = 2 { in 4S }
Principal Quantum no = 4
hence, period of Ca is 4th

PREDICTION of GROUP
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The orbital { S, P , d , or f } which receives the last electton represents the block of the element.
➡ The group of the element is predicted from the block of the elements as : -

(1) if the element belongs to S - block , it's group number is equal to the number of valance electrons .

(2) if the element belongs to P -block ,
Group number = 10 + number of valance electrons
= 10 +nS electrons + nP electrons

(3) if the elements belongs to d -block ,
Group number = number of electrons in (n -1)d subshell + number of electrons in nS subshell .

(4) if the element belong to f - subshell , group number is always 3 .