Proton, Electron and Neutron: Mass and Charge Compared
Chemistry · Structure Of Atom · NEET
An atom has three main particles. The proton has a +1 charge, the electron has a -1 charge, and the neutron has no charge (it is neutral). The proton and neutron have almost the same mass, but the electron is about 1836 times lighter than a proton. Memory hook: "PEN" - Proton Positive, Electron less mass, Neutron no charge.
Proton (+1) and neutron (0) have almost equal mass (~1 u) and sit in the nucleus; the electron (-1) is drawn tiny because it is about 1836 times lighter.
Your doubts, answered
Is the mass of a proton and a neutron exactly the same?
No, they are almost the same but not exactly equal. A proton has mass about 1.672 x 10^-27 kg and a neutron about 1.675 x 10^-27 kg. The neutron is very slightly heavier. For NEET, you treat both as roughly 1 u (one atomic mass unit), so we usually say their mass is nearly equal.
Which is heavier, a proton or an electron, and by how much?
A proton is much heavier than an electron. A proton is about 1836 times heavier than an electron. So the electron's mass is very small compared to the proton. This is why almost all the mass of an atom is in the nucleus (protons + neutrons), not in the electrons.
Why do we say the mass of an electron is negligible?
Because it is about 1836 times smaller than a proton. Electron mass is about 9.11 x 10^-31 kg, while a proton is about 1.67 x 10^-27 kg. When we add up the mass of an atom, the electrons add so little that we can ignore them. That is why atomic mass is counted mostly from protons and neutrons (nucleons).
What is the charge of proton, electron and neutron in coulombs?
A proton carries +1.602 x 10^-19 C (positive). An electron carries -1.602 x 10^-19 C (negative, same size, opposite sign). A neutron carries 0 C (no charge). Because proton and electron charges are equal in size but opposite, a neutral atom has equal numbers of protons and electrons.
Does a neutron have any charge at all?
No. A neutron has zero charge; it is neutral. That is where its name comes from. A neutron only adds mass to the nucleus, it does not add any charge. So changing the neutron number changes the mass number but not the identity or the charge of the atom.
Why is the electron's charge negative but its size same as the proton?
By convention, the electron was defined as negative and the proton as positive. Their charge magnitudes are exactly equal: 1.602 x 10^-19 C. Only the sign is different. This equal-and-opposite charge is why atoms are electrically neutral when protons equal electrons.
⚠️ The NEET trap ✗ Choosing that the proton is heavier than the neutron, or that the electron's charge is smaller in size than the proton's charge. ✓ The neutron is very slightly heavier than the proton (both about 1 u), and the electron's charge is equal in size to the proton's charge (1.602 x 10^-19 C), only opposite in sign. 🧠 NTA loves the wording 'equal magnitude, opposite sign' for charge, and 'neutron slightly heavier' for mass. Do not confuse mass order with charge order.
Real NEET questions
2020
The number of protons, neutrons and electrons in ^{175}_{71}Lu, respectively, are:
A · 71, 71 and 104
B · 175, 104 and 71
C · 71, 104 and 71 ✓
D · 104, 71 and 71
Solution: In the symbol ^A_Z X, Z = atomic number = number of protons, and A = mass number = protons + neutrons. Here Z = 71, so protons = 71. Neutrons = A - Z = 175 - 71 = 104. In a neutral atom, electrons = protons = 71. So the answer is 71 protons, 104 neutrons, 71 electrons, which is option C. This works because the proton carries the +charge, the electron carries the equal -charge, and the neutron (no charge) only adds to the mass number.
Solved Structure Of Atom NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
