Atomic theories

Dalton (1805)

He created a model to explain three important laws of atoms:

    Definite composition

    multiple proportions (when two atoms meet their mass is the sum of their individual masses)

    conservation of mass

*His model fit these laws

His model was the billiard ball:

    Matter is composed of indestructible, indivisible atoms, which are identical for one element but different to other elements

Thompson

He found that matter contains electrons

    (therefore must contain + charges to balance - charges)

He fired a ray of electrons (cathode ray) and found that they gravitated towards a positively charged plate

His model was the Chocolate chip cookie:

    Matter is composed of atoms that contain electrons embedded in a positively charged     material. (electrons = chocolate chips, positively charged material = cookie)

Rutherford

(He was known for radiation.) In his experiment he fired alpha particles (He²+ ions; positively charged particles) at gold foil and observed that most passed through, but that some would occasionally reflect back. He then deduced that the atom was mostly empty space, with a positively charged particle at the center.

His model was the Atomic model:

    The atom is mostly empty space with a positively charged particle at the center, surrounded     by orbiting electrons along the outside.

Chadwick (neutrons)

    How can a hydrogen atom have one proton and a mass of one, and a helium atom have 2     protons but a mass of 4?

Chadwick proved the existence of neutrons by observing a particle with a charge but no mass.

Niels Bohr

He addressed the problems with Rutherfords model with his own:

    Electrons should fall into the nucleus (like + and - sides of magnets)

He fixed this with his own model, The Planetary Model:

    Electrons exist around different energy levels around the nucleus (energy holds them there). When an electron drops a level, it releases a specific amount of thermal and light energy. (So when you add an energy level it takes in heat and light)

Schrödinger

He found that though electrons have distinct energy levels, they behave more like waves than particles.

His model was the Electron Cloud (aka. Quantum Mechanical):

    this model is based on mathematical equations that let us predict where an electron is most likely to be found.