Question

An element X has mass number 35 and the number of neutrons is 18 . group no and period of X .

Answer 1

good morning.

I am meritkshitij here.

given,

mass number of x=35

and,no. of neutron=18

thus,atomic no.=mass no.-- no. of neutron
=35-18

=17


now,

let's try it electronic configuration

18=2,8,7

clearly,they are 3 shells so,period is 3

now,group =10+7=17


WHY?

to find group no. add 10 to the no. of electron of last shell of an element only if it is greater than 2.

Answer 2

Given , Mass number ( A) = 35 .
Number of neutrons (n) = 18 .

Atomic number ( Z) = ?

A = Z + n
35 = Z + 18
Z = 17 .

Atomic number = 17 .

So, The element X is Chlorine, with valency 1 .

Group number = 8 - 1 = 7A group.

According to recent changes by IUPAC, Group number of Chlorine = 7+10 = 17 ( D block also given continuous numbering)

Regarding it's period,

Write down it's electronic configuration.

E. C = 1s² 2s²2p^63s²3p^5

Writing down distribution of electrons,

Cl = 2 , 8 , 7 .

Hence, Electrons are present in 3rd shell so, It's period is 3 .