ATOMIC THEORY TIMELINE

DEMOCRITUS

• He was the first to introduce the idea of an atom
• Though that if he kept dividing something he would reach an indivisible thing
• He called this indivisible and indestructible thing an atom
• But he could not explain the behavior of atoms
• "Nothing exists except atoms and empty space; everything else is opinion"

DALTON

• Began to develop the modern atomic theory
• All elements are made of indestructible atoms
• All atoms of a specific element are identical
• Compounds are made of whole number ratios of atoms
• Mathematically found the relative masses of atoms. H=1amu

THOMSON

• Discovered the existence of electrons and created the Plumb Pudding Model
• Proved there was something smaller than the atom and that it was breakable
• Said: negatively charged electrons floated in a positively charged electric field
• Said: mass of the atom must be due to the mass of electrons
• Said: there must be a lot of empty space within an atom.

RUTHERFORD

• Used a gold foil experiment and discovered the nucleus of an atom
• Nucleus has practically the whole mass of the atom
• Nucleus is positively charged to balance out the negative chare of electrons
• Discovered the existence of protons and neutrons
• Said that both neutrons and protons are 1amu and electrons are not even 1amu

BOHR

• Proposed the idea of orbitals and created the Bohr Model
• Explained how electrons react to light
• Orbitals have specific energy levels
• Electrons switched from orbital to orbital with a specific amount of quantum
• His work mainly explained the behavior of hydrogen

SHRÖDINGER

• Discovered equation to find the probability of finding an electron in an atom
• Also made Quantum Mechanical model which has shells, subshells & orbitals
• Subshells are identified by letters s,p,d,f
• Orbitals: regions with high probability of having electron; they have specific shapes
• Each shell has one or more subshells