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Chemistry 103


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J.J. Thompson
o 1897
o Mass-to-charge ratio
o Cathode Rays
R Milliken
o 1909
o Oil Drop Experiment
o Charge of Electron
o Mass of electron can be determined
o 1886
o Discovered protons in the canal rays
o Protons moved towards negatively charged cathode
James Chadwick
o 1932
o Neutron
o Observed protons being emitted from paraffin wax target
o Only neutral charged particle could have done it
o 1911
o Gold foil experiment
o Particles deflected from path
o Discovered nucleus to be concentrated and tiny
Atomic mass defect
o Sum of all the masses of particles in the nucleus (protons + neutrons) is actually more than the true weight of the nucleus
o The “missing mass” is due to the bonding energy of the nucleus , where energy is related to mass by E=mc^2
Standard enthalpy of formation
o The enthalpy change for the formation of 1 mol of (molecule) from its elements at their standard state conditions (25°, 1atm)
Specific heat
o The quantity of heat required to raise the temperature of 1g of a substance by 1K within 1 phase
Photoelectric effect
o The experiment that demonstrated that light has particle-like behavior
 When light is shined on certain metals, nothing happens until the wavelength reaches a threshold value
 After threshold (different for every metal), electrons can be ejected, producing a current
 When the intensity of the light is increased, the current increases proportionally
Electron diffraction experiment
o Davisson and Germer
o 1927
o Wave-light nature of electrons
Failure of Bohr Model
o Only works for one electron atoms
o Electrons don’t really travel in circular orbits around the nucleus
Three quantum numbers
n, l, ml
 describes the energy of the orbital
 any nonzero positive integer
 describes the shape of the orbital
 any integer between 0 and n-1
 describes the direction of the orbital
 any integer between –l and +l, including 0
Pauli Exclusion Principle
o No two electrons in an atom or ion can have the same set of four quantum numbers (n, l, ml, and ms)
Hund’s Rule
o In an atom or ion in which A.O’s of equal energy are to be filled by electrons, the energetically preferred order of filling is such that as many electrons remain unpaired as possible
o Electrons will occupy available equal-energy A.O’s singly (to give a maximum number of unpaired spins) before electrons spin-pair with opposite spins
Longest lambda -->
lower energy
Low n to high n (n=1 --> n=3)
High n to low n (n=3 --> n=1)

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