A monatomic ion has a charge of +1

A monatomic ion has a charge of +1. The nucleus of the ion has a mass number of 85. The number of neutrons in the nucleus is 1.30 times that of the number of protons. How many electrons are in the ion? What is the name of the element?

Solution:

From the question, we know that there are 1.30 times the number of neutrons as there are protons. Let, p, represent the number of protons. Thus we can say, 1.30p is the number of neutrons. The total mass is 85, thus we can write:

85=1.30p+p

(remember, there is a +1 charge as stated in the question)

85=2.30p

Solve for p, and we get:

p=36.95 however, we will round up, giving us 37. In the periodic table, this element is rubidium (Rb). As the ion has a +1 charge, there is one less electron, meaning there are a total of 36 electrons.

This question can be found in General Chemistry, 9th edition, chapter 2, question 2.128