Question

By using the periodic table how did you determine how many neutrons are in the most common isotope of an element?

a. Subtracting protons from electrons
b. Subtracting protons from the atomic mass
c. Subtracting electrons from the atomic mass
d. Adding protons to electrons

Answer 1

To find the number of neutrons in the most common isotope of an element, subtract the atomic number from the atomic mass found on the periodic table.

Step-by-step explanation:

To determine how many neutrons are in the most common isotope of an element using the periodic table, you should choose option b: Subtracting protons from the atomic mass. The atomic number of an element is equal to the number of protons and is also indicative of the number of electrons in a neutral atom.

By looking at the atomic mass, which represents the mass number of the most common isotope and is the sum of protons and neutrons and subtracting the atomic number from this mass you can establish the number of neutrons. For instance chlorine (Cl) has an atomic number of 17 and an average atomic mass of approximately 35.45 which is based on the isotopic composition of Cl. However the most common isotope of Cl has a mass number of 35 (17 protons plus 18 neutrons).