ATOMIC THEORY TIMELINE

DEMOCRITUS

BEGINNING OF THE ATOM

• The atom was first proposed by Democritus, a Greek philosopher (460-370 B.C.)
• Democritus was known as the 'laughing philospoher'.
• He insisted that our world was made of the ultimate particle.
• This particle is called an atom, from the Greek word "atomos" meaning indivisible.
• Democritus explained the atom was infinitely small.

DALTON ADVANCES ATOMIC THEORY

DOLTON'S THEORY

• John Dalton (1766-1844) proposed his atomic theory
• 1)Each element is composed of tiny, indestructible spheres called atoms
• Dalton used the name Democritus brought forth
• 2) All atoms of an element are identical (same physical and chemical properties).
• Atoms combine in simple, while number ratios to form molecules and compounds.

DALTON CONTINUED

• Dalton used assumed formulas to find the relative masses of atoms.
• He based his scale on Hydrogen which has one AMU.
• Many of the assertions John Dalton made were wrong, but his ides were essential to atomic theory.

J.J.THOMSON

J.J. THOMSON TAKES THE NEXT STEP

• Joseph John Thomson (1856-1940) advanced atomic theory.
• Thomson useda cathode and anode to project light onto a phosphorus coat.
• He then manipulated the light by means of a positive and negative plate.
• He concluded that the atom's structure has electrons suspended in a positively charged electric field.
• To further increase his knowledge Thomson performed more experiments

THE PLUM PUDDING MODEL

• Thomson expressed his ides with the plum pudding model.
• He affirmed with Dalton that the atom was indestructible.
• He also predicted that the mass of the atom is due to the mass of the electrons.
• As well as there must be a lot of empty space in the atom.
• His experiment was model since he had no knowledge of the orbits within an atom.

RUTHERFORD

RUTHERFORD DISPROVES THE PLUM PUDDING MODEL

• Ernest Rutherford (1871-1937) performed an experiment that disproved the plum pudding model and advanced atomic theory
• In his experiment Rutherford shot alpha particles through gold foil assuming every electron would pass through
• What he found was that 98% passed through while 2% were deflected and 0.01% bounced back.
• He did not believe these resluts
• From these results Rutherford concluded that in the center of the atom was the nucleus, a small dense region.

RUTHERFORD CONTINUED

• If the plum pudding model was correct than all the alpha particles should have passed through
• Rutherford assumed the nucleus consisted of nearly all the atom's mass.
• He concluded that the nucleus had a positive charge as well.
• An incorrect assumption he made was that electrons were scattered in space aroud the nucleus, with protons inside.
• A correct assumption he made was that in the nucleus there were protons, and his discovery, the neutron.

BOHR MODEL

THE BOHR MODEL

• Neils Heinrik David Bohr (1885-1962) proposed the Bohr model
• This model organized electrons into orbitals, each with a specific energy.
• The farther the electron from the nucleus, the more energy it has.
• When an electron raises energy and gains a quantam it is in an excited state.
• When it returns to the ground state, it emits light.

SCHRÖDINGER

SCHRÖDINGER'S PROBABLITIY

• Erwin Schrödinger (1887-1961) is the father of quantum mechanics.
• This is science that involves finding the probability of where an electron is at a particular time.
• Schrödinger used orbitlas as a place where electrons are 90-95% of the time.
• The orbitals were organized from sub levels s, p, d, f
• Each sub level has a specific amount of orbitals