Question

Consider  ¹⁴N and ¹⁵N.  What exactly do the 14 and 15 signify?  What causes these two forms of nitrogen to have different numbers?  

Answer 1

14 and 15 signify the mass number of N.

they are isotopes of N.

atomic number = proton number = 7

mass number = proton number + neutron number

mass number tells us number of particles in the nucleus.

There are 14 protons and 7 neutrons in a nucleus of N-14 and 15 protons and 8 neutrons in a nucleus of N-15.

Isotopes have same atomic number or proton number but have different mass number.