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460 BCE
Democritus
Used the word "atom" for the first time, which means indivisible, indestructible and unchangeable.
Description of the model: Democritus’s model stated that matter consists of invisible particles called atoms and a void of empty space.
Main contribution: He provided the word atom that we use nowadays.
What was wrong? Atoms are divisible because they are made up of protons, neutrons, and electrons.
[http://www.abcte.org/files/previews/chemistry/s1_p1.html] -
Dalton's Billiard Ball Model
-Atoms are indivisible and indestructible.
-Atoms of different elements combine forming a compound.
Description of the model:He used wooden balls to model atoms.
Contribution: He explained the laws of conservation of mass, definite proportions, multiple proportions, along with other observations and that all elements are made up of atoms.
What was wrong? The indivisibility of an atom, an atom can be further subdivided into protons, neutrons and electrons. -
Thomson's Plum Pudding Model
-Atoms are solid positive spheres with negative electrons on the surface.
-He discovered the electron when he was experimenting with gas discharge tubes for what he called the movement cathode rays.
Model: Thomson discovered the electron by experimenting with a cathode ray, tube.
Contribution: He discovered electrons and discovered cathode rays.
What was wrong? Failed to recognize the positive charges in the atom as particles.
[http://thehistoryoftheatom.weebly.com/jj-thomson.html] -
Rutherford's Nuclear Atom
-Proposed that atoms consisted of a small dense center filled with positive charges for what he named nucleus.
-Negatively charged electrons were scattered around the nucleus.
Model: Rutherford fired tiny alpha particles at solid objects such as gold foil.
Contribution: Discovered protons.
What was wrong? Rutherford's model didn't account for the properties of electrons. He also concluded that atoms are mostly made up of empty space.
[http://thehistoryoftheatom.weebly.com/lord-rutherford.html] -
Bohr's Solar System Model
-Electrons moved in energy levels around the nucleus, called electron shells.
-Electrons can jump from a lower to a higher orbit by absorbing energy, of heat, light or electricity.
Model: An expansion on the Rutherford model of 1911.
Contributions: The view of motion of the planetary electrons bring the model in line with regular patterns of light emitted by hydrogen atoms.
What was wrong? Bohr's model was two-dimensional and atom's are three-dimensional. -
Schrödinger's Electron Cloud Model
-Levels are divided into sublevels & sublevels are divided into orbitals.
-We cannot know the location of an electron.
Model: The quantum mechanical model doesn't define the exact path of an electron, but, predicts the odds of the location of the electron.
Contribution: Discovered that electrons don't move in orbits.
What was wrong? Schrödinger's model assumes that electrons are waves and tried to describe orbitals, where electrons are most likely to be found. -
References
Sarkar, P. (2016, January 18). What are the drawbacks of Bohr's atomic model? Retrieved March 9, 2019, from https://www.quora.com/What-are-the-drawbacks-of-Bohrs-atomic-model. Augustyn, A. (2018, December 28). Bohr atomic model. Retrieved March 09, 2019, from https://www.britannica.com/science/Bohr-atomic-model. The Quantum Mechanical Model
http://www.dummies.com/how-to/content/atomic-structure-the-quantum-mechanical-model.html
