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Democritus Atomic Philosophy   (460 BC - 370 BC)

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Democritus Atomic Philosophy   (460 BC - 370 BC)

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- He believed that atoms were indestructible and indivisible.
- He lacked experimental support because his approach was not based on the scientific theory.

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- John Dalton used Democritus's idea and used the scientific method and came out with a whole new theory.
- 1. All elements are composed of atoms
-2. atoms of the same element are identical. The atoms of any one element are different from any other element
- 3. Atoms of different elements can be physically mixed together or can chemically combine in simple whole- number ratios to from a compound
- 4. Chemical Reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element.

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- Electrons - negatively charged subatomic partials.
- He performed experiments that involve passing electric currents through gasses at low pressure. He sealed the gasses in tubes and at the bottom there were metal disks called electrodes. - Thompson knew that opposites attract tiny negatively changed participial moving at high speed. He called these particles Corpuscles aka Electrons.
- Thompson concluded that electrons must be parts of the atoms of all elements.
- Electrons were stuck to the lamp of a positive charge similar to the raisins stuck in the dough.

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- Carried out experiments to find the quantity of charge carried by electrons.
- An electron carries one unit of negative charge, and its mass is 1/1840 the mass of a hydrogen atom.

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- He found a way to reverse the direction of the Cathode ray and he called these Canal rays and concluded that they were made of positive particles. Canal Ray

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- confirmed the existence of the neutron - a particle with no charge and the same mass unit equal to the proton

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- - After experimental test to find the current theory of atom structure, he proposed that the atom was mostly empty space which explained the lack of deflection of most alpha particles.
- All positive charge and almost all the mass are concentrated in a small region that has enough positive charge to account for the great deflection of some alpha particles
- He called this region the nucleus. - His model was also known as " The Nuclear Atom"
- In the nuclear atom, the protons and neutrons are located in the nucleus. The electrons are disturbed around the nucleus and occupy almost all the volume of an atom.
- the nucleus is tiny to the atom as a whole.
- model was left unfinished.
- the model couldn't explain the chemical properties of elements

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- proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.
- Each electron in his model had a fixed energy, and the energies an electron could have is called energy levels .
- gave results in agreement with experiments on hydrogen atoms, yet it failed to explain for energies absorbed and emitted, and with more than one electron .

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- used the results of past experiments to form a new equation describing the behavior of the hydrogen atom.
- the quantum mechanical model - comes from mathematical solutions to the Schrodinger equation
- The model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.
- The model shows how the electron is moving around the nucleus is similar to the motion of a propeller blade.