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460 BCE
Democritus
Democritus, a Greek who lived from 460 BCE to 370 B.C., developed a new theory of matter; his ideas were based on reasoning rather than science. -
442 BCE
Democritus Model
Democritus’s model stated that matter consists of invisible particles called atoms and an empty space. He said that atoms are indestructible and unchangeable. and that they were homogenous, meaning they have no internal structure. His atomic model was a solid particle, and stated all atoms differ in size, shape, mass, position. However, he was wrong due to the lack of charge, electrons and empty space inside the particle rather than exterior of it. -
John Dalton
John Dalton (1766-1844), investigated into the great depths of chemistry. He came up with a theory on the smallest particles in the universe, of what makes up what we call "matter". All matter consists of indivisible particles. Dalton gave the name to these minute particles, the atom.There are different types of atoms, these are called elements. Hydrogen, oxygen and nitrogen are examples of elements. Each of these elements is different from one another only by its weight. -
Billiard Ball Model or Dalton's Model
- All elements are made up of atoms.
- It is impossible to divide or destroy an atom.
- atoms of the same element are alike.
- Atoms of different elements are different.
- Atoms of different elements combine to form a compound. These atoms must be in definite whole number ratios. Chemical reactions occur when atoms are separated, joined, or rearranged.
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Joseph John Thomson
Thomson's electron came from his work with an experiment: the cathode ray tube. For years scientists had known that if an electric current was passed through a vacuum tube, a stream of glowing material could be seen. Thomson found that the mysterious glowing stream would bend toward a positively charged electric plate. Thomson theorized tthat the stream was in fact made up of small particles, pieces of atoms that carried a negative charge. These particles are electrons. -
Ernest Rutherford
Rutherford performed a series of experiments with radioactive alpha particles. While it was unclear at the time what the alpha particle was. Rutherford fired tiny alpha particles at solid objects such as gold foil. He found that while most of the alpha particles passed right through the gold foil, a small number of alpha particles passed through at an angle and bounced straight back. -
Niels Bohr
The Bohr model was based on his observations of the atomic emissions spectrum of the hydrogen atom. When white light is diffracted with a prism, all the colors of the visible spectrum can be seen. Each color corresponds to a specific amount of energy; however when the light given off by the hydrogen atom was passed through a prism, only certain colors of light could be seen. His expriment helped to see the different properties of the atom. -
Erwin Schrödinger
chrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom. Unlike the Bohr model, the quantum mechanical model does not define the exact path of an electron, but rather, predicts the odds of the location of the electron. This model can be portrayed as a nucleus surrounded by an electron cloud. -
Plum Pudding Model or Thomson's Model
Thomson’s model was known as the "Plum Pudding Model” (or "Raisin Bread Model.") As each atom was a sphere filled with a positively charged fluid, known as the “pudding”. Scattered in this fluid were negatively charged electrons. This means that the electrons were all around the surface. He was wrong, since the electrons are not found in the atoms surface, but in its sorroundings. -
Planetary Model or Rutherford's Model
Rutherford proposed that atoms consisted of a small dense center filled with positive charges. He named it the nucleus. He then said that negatively charged electrons were scattered surrounding this dense, positively charged center. He stated these negatively charged electrons were held in orbit by the positively charged nucleus, due to the electrical forces. However, the model is wrong due to the movement of electrons. -
Atomic Model, Energy Level Model or Bohr's Model
He stated they moved in circular orbits (energy levels) around the nucleus, these called electron shells. These shells were at set distances from the nucleus and were the same for all atoms. He stated they became larger the further away they are from the nucleus, and that electrons furthest from the nucleus have higher energy. He identified that an electron can jump from a lower orbit to a higher orbit by absorbing energy, this can be done in the forms of heat, light or electricity. -
Qunatum Mechanical Model or the Schrodinger Model
The cloud model represents a sort of history of where the electron has probably been and where it is likely to be going. The red dot in the middle represents the nucleus while the red dot around the outside represents an instance of the electron. Imagine, as the electron moves it leaves a trace of where it was.
