Determining the Number of Subatomic Particles in Atoms

Question

Which of these atoms has the largest number of neutrons in the nucleus?

More than one may apply.

 

149Nd

148Eu

162Ho

157Dy

159Gd

Answer 1

In order to determine the number of neutrons in an atom, you need subtract the atom's number of proton (the atomic number) from the atom's mass number for the particular isotope.

 

The mass number has to be given to you. It is the number in the upper left in standard notation (e.g. ¹⁴⁹Nd has 149 nucleons = protons + neutrons).

 

The atomic number is sometimes given in the isotope notation. It would be the bottom left number, which is not given to you in the problem. So, you need to get the atomic number by determining the element's number in the periodic table. For example, Nd is element 60 on the periodic table, so Nd has an atomic number of 60.

 

To get the number of neutrons in neodymium-149 (¹⁴⁹Nd, or ¹⁴⁹₆₀Nd), you simply need to compute 149-60 = 89.

 

You simply need to follow that procedure to determine the number of neutrons in all of the other isotopes... that is: 1) get the atomic number for each element; and 2) subtract that number from the given number of nucleons.