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  2. Discovery of the neutron - Wikipedia

    en.wikipedia.org/wiki/Discovery_of_the_neutron

    The question was challenging to answer because the electron's mass is only 0.05% of the proton's, hence exceptionally precise measurements were required. The difficulty of making the measurement is illustrated by the wide-ranging values for the mass of the neutron obtained from 1932 to 1934. The accepted value today is 1.008 66 Da.

  3. Atomic nucleus - Wikipedia

    en.wikipedia.org/wiki/Atomic_nucleus

    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.

  4. Rutherford scattering experiments - Wikipedia

    en.wikipedia.org/wiki/Rutherford_scattering...

    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.

  5. J. J. Thomson - Wikipedia

    en.wikipedia.org/wiki/J._J._Thomson

    Thomson made the discovery around the same time that Walter Kaufmann and Emil Wiechert discovered the correct mass to charge ratio of these cathode rays (electrons). [35] The name "electron" was adopted for these particles by the scientific community, mainly due to the advocation by George Francis FitzGerald, Joseph Larmor, and Hendrik Lorentz.

  6. Atom - Wikipedia

    en.wikipedia.org/wiki/Atom

    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 ...

  7. Rutherford model - Wikipedia

    en.wikipedia.org/wiki/Rutherford_model

    After Rutherford's discovery, subsequent research determined the atomic structure which led to Rutherford's gold foil experiment. Scientists eventually discovered that atoms have a positively charged nucleus (with an atomic number of charges) in the center, with a radius of about 1.2 × 10 −15 meters × [atomic mass number] 1 ⁄ 3. Electrons ...

  8. Neutron - Wikipedia

    en.wikipedia.org/wiki/Neutron

    Electrons were assumed to reside within the nucleus because it was known that beta radiation consisted of electrons emitted from the nucleus. [46] About the time Rutherford suggested the neutral proton-electron composite, several other publications appeared making similar suggestions, and in 1921 the American chemist W. D. Harkins first named ...

  9. Atomic physics - Wikipedia

    en.wikipedia.org/wiki/Atomic_physics

    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.