ATOMIC THEORY TIMELINE

DEMOCRITUS

• First person to think there is an ultimate particle, atom
• Meaning a particle ends at some point and stops
• "Nothing exists except atoms and empty space; everything else is opinion

DALTON

• Proposed that each element is made of tiny particles called atoms
• All atoms have the same mass, volume, and other physical & chemical properties
• His second theory was not correct
• Atoms combine through simple whole-number ratios to form compounds

THOMSON

• Proposed the atom is unbreakable
• An atom has electrons in a positively charged electric field
• The electrons must be negatively charged this lead to the plum pudding model
• Model proposed that atom's mass is due to the electrons
• It also meant that an atom had a lot of empty space

RUTHERFORD

• Used target "bullets" to shoot through atom to prove plum pudding
• Results: most targets when straight through, a few curved, and a few repelled back
• Experiment lead to discovery of the nucleus, and that it contained protons amd neutrons
• He also discovered that the nucleus holds the mass if an atom
• Electrons weigh 0.00055 amu, protons weigh 1 amu, and neutrons weigh 1.0087 amu

BOHR

• Predicted that electrons travel in orbits around nucleus; farther the electron is the more energy it has
• Only specific orbits with specific energies are allowed in each energy level
• When an atom gains energy the electron moves from a lower energy state to a higher energy state
• The atom went from grounded state to excited state

SCHRODINGER

• Discovered an equation that predicts the probability of an electron's energy and location
• Saw that there are sub-levels within an energy level, the first 4 are s,p,d,f
• Also learned that there are orbitals within the sublevel, 2 electrons fit in one or orbital