What is atomic mass? How is it calculated?

Solution : Here, we are asked to find the differences in the compositions of the given pairs of atomic nuclei. An atom is composed of three main subatomic particles namely protons, neutrons and electrons. The subatomic particles of an atom gives the element's atomic number and mass number. The number of protons in the n ucleus of an atom determines an element's atomic number. The sum of p rotons and neutrons give the atom’s ma ss number. Let’s consider a c arbon atom. C arbon atom with its m ass number and atom number can be represented as : Now, let’s look at the pairs given to find the difference in the composition of the nuclei : : Consider, atom : Bi is the chemical symbol of Bismuth. Bi has an atomic number of 83 and mass number of 210 as shown. Atomic number of 83 indicates, there are 83 protons and 83 electrons. Now we determine the number of neutrons. Number of neutrons = mass number - number of protons = 210-83 = 127. Consider, atom : Pb is the chemical symbol of Lead. Pb has an atomic number of 82 and mass number of 210. Therefore, number o