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Almost coincident with their discovery, neutrons were used by Norman Feather, Chadwick's colleague and protege, in scattering experiments with nitrogen. [91] Feather was able to show that neutrons interacting with nitrogen nuclei scattered to protons or induced nitrogen to disintegrate to form boron with the emission of an alpha particle ...
A model of an atomic nucleus showing it as a compact bundle of protons (red) and neutrons (blue), the two types of nucleons.In this diagram, protons and neutrons look like little balls stuck together, but an actual nucleus (as understood by modern nuclear physics) cannot be explained like this, but only by using quantum mechanics.
Many more types of subatomic particles have been found. Most such particles (but not electrons) were eventually found to be composed of even smaller particles such as quarks. Particle physics studies these smallest particles; nuclear physics studies atomic nuclei and their (immediate) constituents: protons and neutrons.
The prevailing model of atomic structure before Rutherford's experiments was devised by J. J. Thomson. [1]: 123 Thomson had discovered the electron through his work on cathode rays [2] and proposed that they existed within atoms, and an electric current is electrons hopping from one atom to an adjacent one in a series.
The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force. This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed for the electron to escape. The closer an electron is to the nucleus, the greater the ...
[19]: 461 Heavy nuclei carry a large positive charge, hence they require "extra" neutrons to be stable. [19]: 461 While a free neutron is unstable and a free proton is stable, within nuclei neutrons are often stable and protons are sometimes unstable. When bound within a nucleus, nucleons can decay by the beta decay process.
Within a molecule, electrons move under the influence of several nuclei, and occupy molecular orbitals; much as they can occupy atomic orbitals in isolated atoms. [128] A fundamental factor in these molecular structures is the existence of electron pairs .
The true beginning of atomic physics is marked by the discovery of spectral lines and attempts to describe the phenomenon, most notably by Joseph von Fraunhofer. The study of these lines led to the Bohr atom model and to the birth of quantum mechanics. In seeking to explain atomic spectra, an entirely new mathematical model of matter was revealed.