Chemistry · Structure Of Atom · NEET
About 100,000 times, which is 10^5. The atom radius is 10^-10 m and the nucleus radius is 10^-15 m. Divide them: 10^-10 / 10^-15 = 10^5. So the diameter of the atom is roughly 100,000 times the diameter of the nucleus. This is why we say the nucleus is 'tiny' compared to the atom.
NCERT states the radius of the atom is about 10^-10 m and the radius of the nucleus is about 10^-15 m. In other units: the atom is about 100 pm (picometres) and the nucleus is about 1 fm (femtometre, also called 1 fermi). Learn both numbers as a pair, because NEET options often try to swap them.
Because the nucleus is only 10^-15 m but the atom is 10^-10 m. The nucleus sits at the centre and holds almost all the mass, but takes up almost none of the volume. Since volume depends on radius cubed, the nucleus fills only about (10^-15/10^-10)^3 = (10^-5)^3 = 10^-15 of the atom's volume. The rest is space where electrons move. This is why most alpha particles passed straight through the gold foil in Rutherford's experiment.
It is NCERT's way to picture the huge size gap. If you blow up the nucleus until it is as big as a cricket ball, then the whole atom would grow to about 5 km in radius, roughly the size of a large town area. This shows the nucleus is very small and very far from the edge of the atom, with empty space in between.
No, this is the common mix-up. The nucleus is small in SIZE (volume) but it carries almost ALL the mass of the atom. Protons and neutrons in the nucleus are heavy, while electrons in the large outer space are very light. So the nucleus is tiny but heavy and dense; the atom is large but almost empty.
1 fermi = 1 femtometre = 10^-15 m. The nucleus radius is about 1 fermi, so 'fermi' is the natural unit for nuclear size. For atom size we use angstrom: 1 angstrom = 10^-10 m, so an atom is about 1 angstrom. Knowing these unit names helps you read NEET options quickly.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
About 10^5, meaning the atom is roughly 100,000 times wider than the nucleus (atom 10^-10 m, nucleus 10^-15 m).
About 10^-15 m, which is 1 femtometre or 1 fermi. It holds almost all the mass of the atom in a very small volume.
About 10^-10 m, which is 100 picometres or 1 angstrom. Most of this space is where the electrons move, and it is nearly empty.
No. The nucleus is small in volume but contains almost all the mass. The atom is large in size but very light in the outer region where only electrons are present.
It explains Rutherford's alpha scattering result (most particles pass through empty space) and is directly asked as a numbers or ratio question. Remembering 10^-10, 10^-15 and the 10^5 ratio saves time.
