Question

An atom has 17 protons and 18 neutrons. Which of the following could be the symbol for that atom, including its mass number?

Answer 1

Answer: The atomic symbol is $_{17}^{35}\textrm{Cl}$

Explanation:

Atomic number is defined as the number of protons or electrons that are present in a neutral atom.

Atomic number = number of protons = number of electrons

Atomic mass is defined as the sum of number of protons and neutrons that are present in an atom.

Atomic mass = Number of protons + Number of neutrons

General representation of an isotope is $_Z^A\textrm{Z}$

where,

A = atomic mass

Z = atomic number

X = symbol of an atom

We are given:

Number of protons = atomic number = 17

Number of neutrons = 18

Atomic mass = 17 + 18 = 35

Hence, the atomic symbol is $_{17}^{35}\textrm{Cl}$

Answer 2

An atom of chlorine-35 contains 18 neutrons (17 protons + 18 neutrons = 35 particles in the nucleus) while an atom of chlorine-37 contains 20 neutrons (17 protons + 20 neutrons = 37 particles in the nucleus). Adding or removing a neutron from an atom's nucleus creates isotopes of a particular element.