Question

An element has mass number 35 and atomic number 17 , find:

(1) the number of neutrons in the element, and

(2) the number of electrons in theoutermost shell

Answer 1

Mass number= number if protons+ number if neutrons
atomic number= number if protons/elections

1) number of neutrons is 35-17 = 18
2) number if elections present in last shell= 7
Therefore the valency if this element is -1

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Answer 2

GIVEN -

Mass number is 35

Atomic number is 17

METHOD -

To find the neutron number of the element, we have to subtract atomic number from the mass number.

(1) Neutron number = 35 - 17

•                              = 18

Therefore, 18 is the neutron number.

(2) The electronic configuration of the atomic number 17 will be  2, 8, 7.

So the electron number which is present in the last shell is 7.

Hence, in this way we can find out the electrons of the last shell and the neutron number.