Question

A carbon atom has a mass number of 12. How many protons and how many neutrons does it have?

Answer 1

Hint: The answer lies in basic concept of chemistry which makes use of formula to find the number of protons, neutrons and electrons which is based on the periodic table and the formula is therefore given by, $n_p=m-n_n$

Complete answer:
In the lower classes of chemistry, we are familiar with the concepts of atoms, its structure, composition and also the properties about it from the basic concepts of chemistry which we studied in the chapters of chemistry.
We shall see what is an atom and what its constituent parts.
- An atom is the smallest particle that can exist which builds the entire universe and each atom has the size of about 100 picometers. It is composed of a central nucleus in which positively charged species called protons and the neutral species called neutrons are situated.
- The electrons that are negatively charged species that revolve around the orbit of the nucleus in the circular path.
- The atomic number of any atom indicates that number of protons present in their nucleus and also from the facts it is known that the number of protons are always equal to the number of electrons and therefore they are equal.
- Neutrons and protons together are concentrated in the nucleus which gives the mass number to that particular element.
- Therefore, mass of an element and the number of neutrons present can be calculated using the mass number which is given by the formula, $n_p=m-n_n$
- Here, the according to the data given,
Mass of carbon atom = 12 amu
Since, from the periodic table data, the atomic number of carbon is 6 and this implies that the total number of protons in it are 6.
This also means that the total number of electrons in the carbon atom are also 6.
Now, substituting the values in the above formula, number of neutrons can be found and that is,
$$n_n=12-6=6$$
Therefore, the correct answer is, the number of protons and neutrons in a carbon atom with mass 12 is 6 and 6 respectively.

Note:
Note that the unit of atomic mass is amu (atomic mass unit) which is the mass exactly equal to one – twelfth the mass of carbon – 12 atoms. This unit is also written in the form of Dalton units, denoted by ‘D’ or sometimes ‘Da’.