Question

29. A negative ion of an atom of element X has 18 electrons and 16 protons. Calculate the number of electrons and protons in its corresponding atom. Also calculate the number of neutrons, if the mass number is 2 units more than double the number of protons.

Answer 1

• The number of protons present inside the nucleus is called atomic number which is represented by Z.
• Number of protons = Number of electrons
• Mass number indicates the sum of protons and neutrons present inside the nucleus. It is represented by A.

Mass number = Number of protons + Number of neutrons

Number of neutrons = Mass number - Number of protons

Given that:

Number of electrons for the negative ion of an atom of element X = 18

Number of protons for the negative ion of an atom of element X = 16.

Number of protons will remain the same whether the element is gaining or losing electrons.

We know that in an atom, number of protons = Number of electrons

So, the number of electrons = Number of protons = 16.

According to the statement given, mass number = twice the number of protons + 2 units

Mass number = (2 × 16) + 2

Mass number = 34

Now, number of neutrons = Mass number - Number of protons

Number of neutrons = 34 - 16 = 18

Therefore,

Number of electrons present in element X = 16

Number of neutrons present in element X = 18.