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Hewitt Chapter 31/32 The development of models that describe the atom…
Hewitt Chapter 31/32
The development of models that describe the atom
"Billiard Ball" atom model
Solid, considered unbreakable
Electron
1752 by Benjamin Franklin
1987 Joseph John Thomson showed cathode rays were particles smaller & lighter than atoms
1909 Robert Millikan oil-drop experiment calculated numerical value of a single unit of electric charge
"Plum Pudding" atom model
Electrons scattered like raising in a sea of positively charged pudding (light negative charges and positively charged pudding uniformly mix throughout atom
"Planetary" atom model
Atom mostly empty with tiny massive positive nucleus at center and electrons orbit
Neutron
1932 James Chadwick found nucleus of atoms contained neutral particles named neutrons
Atomic Structure
Most of mass in nucleus
Protons (positive) & Neutrons (electrically neutral)
(approx. same mass)
P+N = Nucleons
Form Positive Ions when lose electrons
Form Negative Ions when gain electrons
"Bohr's" atom model
E=
hf
,
h
is Planck's constant, E is energy of light particle and
f
is frequency
Modification of Rutherford's planetary model
Size of electron orbits determined by number of electrical charge in nucleus
Accounts for the chemical properties of elements (eg. group 1 elements have 1 electron on outermost orbit and have similar chemical properties)
Electron standing waveform
Nodes were portion of the wave remains stationary
Combination of two waves travelling in opposite directions
No fraction of wavelength is possible in a circular electron standing wave
Quantum Physical atom model
Erwin Schrodinger & Werner Heisenberg created quantum mechanics, they combined the particle and wave nature of matter mathematically
Describes an electron as a wave function that describes the possible states and calculate the probability of finding an electron at any location around nucleus. electron can be found more frequently in certain regions depending on energy, hence atomic orbitals
