The Atom
Theories and Structure
A. Theories of the Atom
- Greeks
- Democritus
- each type of matter was made of unique, indivisible particles
-
Aristotle
- matter was not made of particles, it was made of continuous substance called hyme
- Dalton
- indivisible
- different elements have different types of atoms
- different types of atoms can physically mix together or combine in simple whole-number ratios to form compounds
- chemical reactions occur when atoms join together, are separated, or are rearranged.
- J.J. Thompson
- discovered electron with cathode ray tube
- Chocolate chip cookie model (electrons are "chips")
- Millikan
- oil drop experiment
- determined mass to charge ratio of electron
- Rutherford
- Gold foil experiment
- Atom is primarily empty space
- Positive nucleus exists
- Bohr
- planetary model
- electrons are arranged in specific energy levels
- Quantum Mechanic Model
- current model
- small, dense nucleus in center
- electrons are likely to be found in electron clouds outside of nucleus
B. Subatomic Particles
- Proton
- found in nucleus
- charge of +1
- mass of 1 amu
- Number of Protons = atomic number (Z)
- determines the identity of element
- Neutron
- found in nucleus
- charge of 0
- mass of 1 amu
- number of neutrons = Mass number(A) - atomic number(Z)
- varying number of neutrons in atoms of the same element results in isotopes
- Electron
- found in electron clouds
- relative mass of 0.002 amu
- if atom is neutral, number of electrons = number of protons
- gain or loss of electrons results in the formation of ions (charged particles)
- Other subatomic particles have recently been discovered
- quarks
- hadrons
- leptons
- positrons
- neutrinos
- many others
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