Chemistry · Structure Of Atom · NEET
A nucleon is the general name for any particle that sits inside the nucleus. Both protons and neutrons are nucleons. So "nucleon" is like a family name, and "proton" and "neutron" are the two members. When a question says "number of nucleons," it just means protons + neutrons added together.
No. This is the most common mistake. Electrons move around outside the nucleus, so they are NOT nucleons. Only protons and neutrons are nucleons. Remember: nucleons live IN the nucleus; electrons live OUTSIDE it. NEET often tries to trap you here.
Yes. Mass number A is defined as the total number of nucleons, that is protons + neutrons. A = Z + N, where Z = number of protons (atomic number) and N = number of neutrons. Electrons are almost massless, so they are not counted in A. This is why A is a whole number.
The nucleus is the tiny centre of the atom. The nucleons are the particles that make up that centre. So the nucleus is the "box" and the nucleons (protons and neutrons) are the "things inside the box." One nucleus contains many nucleons.
Look at the top-left number in the symbol (A/Z X). The top number is the mass number A = total nucleons. For Lu-175, A = 175, so there are 175 nucleons. To split them: protons = Z (bottom number = 71), and neutrons = A - Z = 175 - 71 = 104. So 71 protons + 104 neutrons = 175 nucleons.
The number of protons, neutrons and electrons in Lu-175 (A=175, Z=71), respectively, are:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Because they are the only two particles found inside the nucleus. The name comes from "nucleus." Electrons stay outside, so they are left out.
An electron has almost no mass (about 1/1836 of a proton). So its mass is ignored. Only the heavy protons and neutrons decide the mass number A.
No. Isotopes have the same protons but different neutrons, so they have different total nucleons and different mass numbers. Example: protium, deuterium and tritium all have 1 proton but 0, 1 and 2 neutrons.
Almost every "find protons, neutrons, electrons" question uses this: nucleons = protons + neutrons = mass number. Get this right and you can solve symbol-notation and isotope questions quickly.
