Question

What is the mass number of boron?

Answer 1

Well it depends on the isotope....

Explanation:

`Z=5`, and thus WE KNOW that we got the element boron.

To a first approx. `""^11B` is 80% abundant, and clearly (why?) this isotope has 6 nucular neutrons and thus a mass number of `11`.....and `""^10B` is 20% abundant, and clearly (why?) this isotope has 5 nucular neutrons and thus a mass number of `10`; and a neutron is simply a massive nuclear particle with ZERO electronic charge.

Do you agree?

Answer 2

The mass number of the most common isotope of boron is 11.

Please see the more detailed explanation below.

Explanation:

This is a slightly tricky question, because a mass number is for a particular isotope of an element, not the element itself.

Element number 5 is boron (B). That means every atom of boron has 5 protons.

The most common isotope (about 80% of naturally occurring boron) of boron has 6 neutrons too, for a total of 11 nucleons (protons + neutrons). Its mass number is 11.

Some naturally occurring boron (about 20%) has 5 neutrons, for a total of 10 nucleons, and a mass number of 10.

It is also possible to make isotopes with more than 6 or less than 5 neutrons.

The mass number of the most common isotope of boron is 11.