Concept of Mass of Number

The great scientist Ernest Rutherford who discovered the nucleus by splitting atoms using the gold foil experiment in the year 1911, is the one who came up with the idea of mass number. As of before, John Dalton had already proposed the theory on atomic weights, but Rutherford worked his way and came up with the Mass number, which later on was adopted by the society. As we can see all the advancements in chemistry, all these basic concepts remain the key ground for research. 

What Do You Know By Mass Number?

An atom consists of a nucleus within the nucleus; there are protons and neutrons with electrons revolving around the nucleus. This is the scientist’s basic idea, and Rutherford explained that Mass number is the total sum of protons and neutrons in an atom. This approximation of mass can easily calculate how many neutrons an element has by simply subtracting the number of protons from the mass number. Protons and neutrons both weigh about one atomic mass unit or amu. So isotopes of the same element will have the same atomic number but different mass numbers.

With the discovery of mass numbers, it became easier to distinguish between atoms as an atomic number never changed but the mass number varied in different isotopes of the same element.

With mass number, we can find the number of neutrons present in the atom using this formula

number of neutrons=mass number-atomic number

This formula can also be written as;

Here,                                               

N-number of neutrons

N =A-Z A-Mass number                      

Z-Atomic number

Given an atomic number (Z) and mass number (A), you can find the number of protons, neutrons, and electrons in a neutral atom. For instance, a lithium atom (Z=3, A=7 ) contains three protons (found from Z), three electrons (as the number of protons is equal to the number of electrons in an atom) and four neutrons (7 – 3 = 4).

This will be more clear with a solved example,

• The element Chromium has an atomic number of 24 and a mass number of 52. Find the number of neutrons in its nucleus.

Ans: let’s apply it in the given formula number of neutrons in a Cr atom=52-24=28.

Are Atomic Numbers and Mass Numbers the Same?

Atomic number and mass number are not the same; the atomic number is the total number of protons in an atom. This helps to distinguish between different elements. For instance, Carbon has an atomic number of 6 because it has 6 protons in its nucleus. Whereas in the case of mass number, it is the sum total of protons and neutrons in the nucleus of the atom, i.e., in Carbon for carbon, the mass number is 12 as it has 6 protons and 6 neutrons in its nucleus.

This doesn’t mean that they can never be the same. By definition, they are different, but there are some cases when the atomic number and mass number become the same; for instance, take the case of hydrogen. in a Hydrogen atom, there are no neutrons, so the atomic number and mass number is 1

How will you represent the mass and atomic numbers in shorthand notation?

In the given picture, you can see that the mass number is represented as subscript occupies the top left, and the atomic number is below the given element.

Atomic Mass And Mass Number Of An Element, Is it the same?

The mass number should never be confused with the element’s atomic weight, which is the ratio of the atomic mass of the different isotopes of that element to the atomic mass(amu). The atomic weight is an actual mass, while the mass number is counted (sum of proton and neutron). The average weight considered in atomic weight keeps on varying, so it is a non-integer, whereas the mass number is a proper integer.

Conclusion:

We can conclude by saying that Mass numbers are of great significance in chemistry. We know how to calculate the mass number, its definition and peculiarities. We have also come to know that the different isotopes and their formation are very closely related to the mass number. It also played an important role in arranging these elements in the periodic table, even the most recent period table. We have also solved numerical problems based on it. The concept of mass numbers has made identifying elements easy.