Atom has a tiny dense nucleus holding nearly all the mass, surrounded by electrons in mostly empty space.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
In the nuclear model the atom has a tiny, dense, positively charged nucleus that contains almost all of its mass, surrounded by electrons in largely empty space. It accounts successfully for the large-angle scattering of alpha particles in gold foil. However, classical electrodynamics predicts that an electron orbiting a nucleus should radiate energy and spiral into the nucleus in a fraction of a nanosecond, which would make atoms collapse. The model therefore could not explain the stability of atoms or their discrete line spectra. Bohr and later quantum mechanics solved this problem by quantizing electron energies.
Key ideas: All positive charge and nearly all mass are in a tiny nucleus; electrons occupy the surrounding space. Size ratio is about 10^5, so if the nucleus were a marble the atom would be a stadium. Number of protons = number of electrons in a neutral atom.
Common mistakes and connections: Classical physics predicts such an atom is unstable since orbiting electrons radiate energy and spiral inward within about 10^-11 s, which students overlook. That contradiction led to Bohr quantization and then quantum mechanics. It also supports using Z and A to describe nuclei.
On a log scale the nucleus is about 10,000 to 100,000 times smaller than the atom, so atoms are mostly empty space around a dense core. The interactive lesson shows this as a live animation or chart.
If an atom were the size of a football stadium, its nucleus would be about the size of a grain of sand at the centre.
Atom has a tiny dense nucleus holding nearly all the mass, surrounded by electrons in mostly empty space.
Nuclear Atom Model is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Atomic Structure & Periodicity first: Neutron, Thomson's Plum Pudding Model, Rutherford's Gold Foil Experiment.
The next topics in Atomic Structure & Periodicity are Atomic Number and Mass Number.
Yes. The interactive lesson includes a self-check question on Nuclear Atom Model, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Nuclear Atom Model is topic 18 of 115 in Atomic Structure & Periodicity.