# What is the mass number for Technetium when the atom has 56 neutrons?

Feb 6, 2016

The mass number of this isotope of technetium is 99.

#### Explanation:

The mass number, A, of an isotope is the number of protons (Z) and neutrons (N) in the nuclei of its atoms.

Technetium (Tc) has atomic number, Z= 43, which means that all of its atoms have 43 protons in their nuclei.

To determine the mass number of this isotope of technetium, add the protons and the neutrons. $\text{A=Z+N}$

$\text{A"_"Tc"=43+56"=} 99$

This isotope of Tc is technetium-99. Its nuclear notation (isotopic notation) is:

$\text{_43^99"Tc}$

Generic Nuclear Notation