Question

For lighter, stable isotopes, the ratio of the mass number to the atomic number is close to acertain value. What is the value? What happens to the value of the mass number to atomic number ratio as stable isotopes become heavier?

Short answer

The ratio of mass number to atomic number is nearly 2. For the isotopes of heavier stable, the ratio of mass to atomic number is more than 2.

Step-by-step solution

Lighter stable isotopes

The proton number is equal to the neutron number. If the proton number (Z) and neutrons are equal, then the mass number can be twice the number of atoms. A is sum of neutrons and protons.

The ratio of the mass number to the atomic number is close to a certain value

The ratio of mass number to atomic number is nearly 2 for lighter isotopes.

$\frac{A}{Z}\approx 2$

Value of the mass number to atomic number ratio as stable isotopes become heavier

The neutron number will exceed the proton number (Z) for heavier stable isotopes. Thus, the mass number can be twice the number of atoms. This will make the ratio of mass and atomic number can be greater than 2.

$\frac{A}{Z}>2$