Question

how to find the periodic numbers and group number of elements in table

Answer 1

for example take sodium

electronic configuration is 1s2 2s2 2p6 3s1
number of valence electrons is 1so it's valency is 1
it. is in 3rd period
it is a s:-block element

Answer 2

the period of elements corresponds to the principle quantum number of the valence shell.
the block of an element corresponds to the type of orbital which receive the last electron.
the group of an element is predicted from the number of electrons in the valence shell or /and penultimate shell as follows:-
• for s- block elements, group number is equal to the number of valence electrons.
• for p- block elements, group number is equal to 10+ number of electrons in the valence shell.
• for d- block elements group number is equal to the number of electrons in a (n-1) d subshell+ the number of electrons in valence shell.
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