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In this model, atoms had their mass and positive electric charge concentrated in a very small nucleus. [3] By 1920, isotopes of chemical elements had been discovered, the atomic masses had been determined to be (approximately) integer multiples of the mass of the hydrogen atom, [4] and the atomic number had been identified as the charge on the ...
Kekulé argued that tetravalent carbon atoms – that is, carbon forming exactly four chemical bonds – could link together to form what he called a "carbon chain" or a "carbon skeleton," to which other atoms with other valences (such as hydrogen, oxygen, nitrogen, and chlorine) could join. He was convinced that it was possible for the chemist ...
The prevailing model of atomic structure before Rutherford's experiments was devised by J. J. Thomson. [2]: 123 Thomson had discovered the electron through his work on cathode rays [3] and proposed that they existed within atoms, and an electric current is electrons hopping from one atom to an adjacent one in a series.
[35]: 118 Moreover, the periodic table could predict how many atoms of other elements that an atom could bond with — e.g., germanium and carbon are in the same group on the table and their atoms both combine with two oxygen atoms each (GeO 2 and CO 2). Mendeleev found these patterns validated atomic theory because it showed that the elements ...
An image from John Dalton's A New System of Chemical Philosophy, the first modern explanation of atomic theory.. This timeline of chemistry lists important works, discoveries, ideas, inventions, and experiments that significantly changed humanity's understanding of the modern science known as chemistry, defined as the scientific study of the composition of matter and of its interactions.
Ions consisting of only a single atom are termed atomic or monatomic ions, while two or more atoms form molecular ions or polyatomic ions. In the case of physical ionization in a fluid (gas or liquid), "ion pairs" are created by spontaneous molecule collisions, where each generated pair consists of a free electron and a positive ion. [5]
1999 Ahmed Zewail wins the Nobel prize in chemistry for his work on femtochemistry for atoms and molecules. [33] 2000 scientists at Fermilab announce the first direct evidence for the tau neutrino, the third kind of neutrino in particle physics. [30] 2000 CERN announced quark-gluon plasma, a new phase of matter. [34]
Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms that have either a deficit or a surplus of electrons are called ions. Electrons that are farthest from the nucleus may be transferred to other nearby atoms or shared between atoms.