What is the number of neutrons in an atom with atomic mass o

What is the number of neutrons in an atom with atomic mass of 35, three energy levels, and 7 valence electrons? 7 17 18 35

Solution

Atomic mass (M) = 35

Energy levels = 3

Valence electrons = 7

no. of neutrons (N) = ?

N = M- n

The number of neutrons is equal to the atomic mass minus atomic number. The atomic number is equal to the number of protons in the atom. The number of protons are equal to the number of electrons. In the given case there are three energy levels. 1st energy level has 2 electrons, 2nd energy level has 8 electrons and 3rd energy level of the valence shell has 7 electrons. Therefore, number of electrons is equal to 17 which would be equal to the atomic number.

Therefore,

N = 35 - 17

= 18

ANSWER : Number of neutrons is 18