Question

$can \: ya \: all \: please \: help$
Which element in the modern periodic table has as many electrons in its second shell as in the first shell? If its athm has 7 neutrons, then find the value of its atomic number and mass number.

Answer 1

beryllium has 4 atomic number

therefore 2 electrons in first shell

and 2 in second shell

if atom has 7 neutrons

mass number= 4 +7 = 11

atomic no = 4

Answer 2

Electronic configuration = 2,2 = Beryllium.

So, Atomic number (Z) = 4

Since neutrons = A-Z = 7

So, A = 7+4 = 11.