Atomic theory - modern models
Rutherford atomic model What Rutherford discovered was that most of the alpha particle "bullets"
passed straight through the gold foil, as though it were empty space.
The occasional particle was diverted from its course by something very
small and dense in the gold atoms. The Rutherford atomic model was also known as the "Rutherford nuclear
atom" and the "Rutherford Planetary Model". In 1911, Rutherford
described the atom as having a tiny, dense, and positively charged core
called the nucleus. Rutherford established that the mass of the atom is
concentrated in its nucleus. The light, negatively charged, electrons
circulated around this nucleus, much like planets revolving around the
Sun.
The Bohr atomic model
Instead, Bohr suggested that an atom's electrons move in orbits of fixed size and energy and that the energy of an electron depends on the size of the orbit. Radiation could only be emitted from an atom when an electron dropped from a higher energy orbit to another lower orbit. Stable atoms have their electrons in the lowest possible energy orbits. This was the first "quantum atomic theory", allowing only certain energy levels to exist within the atom. Today's modern quantum theories are very close to Bohr's ideas.
The modern quantum atomic theory The change from Bohr's model is how electrons occupy space. Scientists now believe that electrons move in regions rather than in orbits and use mathematics and quantum numbers to describe this. Bohr's model is quite adequate for describing the chemical properties of an atom. However, the modern quantum theory allows a deeper understanding of the strange subatomic world of wave/particles and electromagnetic energy.
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