Atomic History and Nuclear Chemistry

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Democritus
the world was composed of tiny particles called atoms
Thomson
discovered the electron by using the cathode ray experiments, developed the Plum Pudding Model
Law of Conservation of Matter
matter is neither created nor destroyed in a chemical reaction
Goldstein
discovered the proton
Bohr
used the concept of energy to make the atom stable
quantum
a discrete packet of energy
quantized energy
energy levels
Quantum Theory
energy exists in steps, it is not continuous
electrons orbit the nucleus in their stable energy levels
absorption and emission
Milikan
responsible for determining the charge, figured out the mass of the electron
Chadwick
discovered the neutron
Rutherford
discovered the nucleus using the gold foil experiment
gold foil
the experiment used to discover the existence of the nucleus
target = gold sheet (few atoms thick)
bullet = smaller particles
results of gold foil
-98% passed straight through = mostly empty space
-2% deflected at angles = something with a positive charge was repelling them
-less than 0.01% bounced off foil and came right back = something very small and very dense is in the atom and
problems with gold foil
1. not an accurate mass- did not add up with the protons- there must be something else in the nucleus (Chadwick then discovered the neutron)
2. instability – electrons were not pulled into nucleus because they were orbiting freely (Bohr discovered that electrons orbit the nucleus in different ranks/levels
absorption
energy in – the electrons jump up an energy level
emission
energy out – the electrons jump down an energy level
atomic number
the number of protons (= the number of electrons in a neutral atom)
isotopes
atoms with the same number of protons, but different numbers of neutrons
ion
an atom in which the number of protons and electrons are unequal
mass number
number of protons and number of neutrons
atomic mass unit (AMU)
one-twelgth the mass of a carbon atom having six protons and six neutrons
atomic mass
weighted average if the masses if the isotopes
(mass isotope A * natural abundance of A) + (mass isotope B * natural abundance of B) +…
need: # of stable isotopes, mass of each isotope, % abundance of each isotope
mass defect
the mass of any nucleus is less than the sum of the separate masses of its protons and neutrons
non-ionizing radiation
can pass through an atom without harming it
-weaker energy/longer wave lengths
-outside of nucleus – energy moving between levels
ionizing radiation
has enough energy to strip the electrons from the atom
– creates ions
-shorter wavelengths/higher energy
– originates from electron movement
nuclear radiation
a change in an atom’s nucleus
-can change one element into another
radioactive decay
-unstable nucleus loses energy by emitting radiation
alpha particle
Helium nucleus, 2 protons + 2 neutrons (2+ charge)
alpha decay
-alpha particle
– not very penetrating, a sheet of paper stops them
if atomic number is greater than or equal to 83
– mass # parent drops by 4, atomic # parent drops by 2
beta negative
too many neutrons, negative charge, no mass, above band of stability, rid of neutrons, mass number stays the same but the atomic number increases by one, neutron converts to a proton in the process
beta positive
too many protons, positive charge, no mass, below band of stability , rid of proton, mass number stays the same but the atomic number decreases by one, proton converts to a neutron
gamma ray
high-energy radiation with no mass and no charge
gamma radiation
-gamma ray
-highly penetrating, no mass and no charge so they can travel through most materials
stability of nucleus
determined by the neutron/proton ratio
non-radioactive = falls within the band of stability
band of stability
– stability of isotopes
– too many protons = need more neutrons to buffer the positive
– too few protons = radioactive
smaller nuclei: Z
1:1 ratio and the isotope is stable
bigger nuclei: Z>/= 20
nuclei gets larger and needs more neutrons to stabilize the protons
elements with Z >/= 83
no stable nuclei wiht an atomic # >/= 83
decay by alpha emission
nuclear decay
Parent Isotope –> Daughter Isotope + High Energy Particle
Half-lives
the time it takes for one-half of a radioactive isotope to decay
AE = Ao * 0.5^t/t1/2
AE = amount of substance left
Ao = original amount of substance
t = elapsed time
t1/2 = half-life of the substance
fission
the nucleus of an atom splits into smaller fragments
-fission reactions can be controlled in nuclear power plants with control rods
-atomic bomb which used chain reactions
fusion
the merging or fusing of nuclei to form one large nucleus
-fusion reactions are uncontrollable and they require such high temperatures that cannot be generated in labs
-hydrogen bomb = used a fission reaction to rise temperature until all the nuclei joined together in one huge nucleus with extreme power and force
Categories: Nuclear Chemistry