CHEMISTRY REVIEW: Atomic Model Timeline

Philosophical Atom Model

The first model of an atom dates back to the times of the ancient Greeks, when Leucippus, a Greek philosopher, first used the word “atom” (The History of the Atom, 2016). Leucippus’s model just stated that an atom is something that is indivisible and that atoms can form different kinds of elements and compounds (2016) . This idea stemmed from theoretical and philosophical thinking, with no scientific basis; therefore, this concept was not embraced until the 19th century when scientists began examining this model more closely (Atomic Structure Timeline).

Dalton Model

John Dalton was an English physicist and chemist in the 18th century that built upon of the theory made by the Greek philosophers (2016). In 1803, Dalton created the Dalton Model of the atom, also known as the Solid Sphere Model (2016). This model claimed that atoms were indivisible and identical between all elements (2016). The Solid Sphere Model also stated that atoms can combine to make more complex structures (Models of the Atom). Although now we know how flawed Dalton’s model is, it was the first truly scientific model of the atom at the time.resized_image2_82baeb3eea64ade049b4f13d3777667c

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Plum Pudding Model

The next influential model of the atom came 101 years after John Dalton’s model, in 1904 (Models of the Atom). This new model was the Plum Pudding Model, created by J.J. Thomson (Models of the Atom). He expanded on Dalton’s model by recognizing the charges in the atom, stating that atoms are mostly positive charges with smaller negative charges throughout them called electrons (2016). In his model, the atom is a spherical structure which itself is completely positive but has electrons embedded in it, thus resulting in a model that looks like plum pudding (Models of the Atom).

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Rutherford Model

The following model of the atom comes from New Zealand born-British physicist, Ernest Rutherford (2016). Rutherford performed the gold foil experiment, in which he shot alpha particles (which have a positive charge) at a gold foil and recorded the result (Atomic Structure Timeline). In his data, he found that most of the particles actually passed completely through the atom, with a few being deflected at great angles and some not passing through the atom at all (2016). These results did not make sense with respect to the Plum Pudding Model; therefore, Rutherford created his own model of the atom in 1911 (2016). This model showed the atom as mostly consisting of empty space, with a positively charged nucleus in the center and much smaller electrons around the nucleus (Models of the Atom). This was a breakthrough in the atom model, but it did not explain the movement of electrons in the atom.

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Bohr Model

Years later Danish physicist Niels Bohr modified the Rutherford Model in order to explain the movement of electrons within the atom (Atomic Structure Timeline). This model was called the Bohr Model, which is also known as the planetary model (2016). In this model, the electrons moved in orbits of fixed sizes and energies around the nucleus (Models of the Atom). This explained the emissions of spectra in some elements; however, this model did not quite make sense in respect to heavier atoms because electrons could not collapse into the nucleus in this model, despite doing so in actual atoms (2016).

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Schrödinger Model

The currently accepted model of the atom was created by Erwin Schrodinger many years later, known as the Schrodinger Model (or the Wave Mechanical Model), it states that electrons do not move in orbits around the nucleus; rather, they move in random waves in a “cloud” (Atomic Structure Timeline). This means that while it is impossible to ever know the exact location of the electron, we do know the probability of the electron being in that cloud (2016). To this day, the Wave Mechanical model of the atom is widely accepted as the closest model to an actual atom, with great evidence to support it.

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References:

  • “The History of the Atom – Theories and Models.” Compound Interest, Compound Interest, 16 Oct. 2016, www.compoundchem.com/2016/10/13/atomicmodels/.
  • Atomic Structure Timeline, atomictimeline.net/
  • “Models Of The Atom.” Properties Of Light: Revision | Geometrical Optics | Siyavula, www.siyavula.com/read/science/grade-10/the-atom/04-the-atom-02.

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