Nuclear Chemistry

Published by admin on

Willhelm Roentgen
(1845-1923) discovered X-rays, a high energy form of light (1895)
Henri Becquerel
(1852-1909) found that uranium ores emit radiation that can pass through objects (like x-rays) and affect photographic plates (1896)
Marie Sklodowska Curie
(1867-1934) Marie and Pierre worked with Becquerel to understand radioactivity. Shared a Nobel prize in physics in 1903. She later won a nobel prize in chemistry in 1911/
E.O. Lawrence
Invented the cyclotron which was used at UC Berkeley to make many of the transuranium elements
The spontaneous breakdown of atomic nuclei, accompanied by the release of some form of radiation (also called radioactive decay)
Time required for half of a radioactive sole to decay
One element being converted into another by a nuclear change
Isotopes of elements that are identified by the number of their protons and neutrons
Decay series
The sequence of Nuclides that an element changed into until It forms a stable nucleus
Radioactive dating
Using half life information to determine the age of objects. C-14/C-12 is common for organic artifacts. Uranium is common for rocks
Nuclear fission
Large nucleus breaking down into pieces of about the same mass
Nuclear fusion
Two or more light nuclei blend to form one or more larger nuclei
Types of radiation
Alpha particles, beta particles, gamma rays
Alpha particles
Same as a helium nucleus, 4/2 He, w a mass of 4 amu. Travels about 1/10th speed of light, most easily stopped of the particles, least dangerous
Beta particles
High speed electrons, 0/-1e, with a mass of 0.00055 amu and travel at nearly the speed of light, they can be stopped by a sheet of aluminum, more penetrating/dangerous than alpha
Gamma rays
Extremely high energy light, y, with no mass, and are the most penetrating (several cm’s of lead are needed to stop them) they can cause severe damage
Positron emission
Emission of positron from nucleus 0/+1e
Electron capture
Inner electrons captured by nucleus 0/+1e, caused when electron becomes proton, outer electron fills vacancy…giving off energy
Variables in half life problems
Total time, starting amount, half life, ending amount
Half life graph characteristics
Time it takes for the amount of substance or the activity of the substance to drop to half is the same WHEREVER you start on the graph. This is a first-order reaction. Half lives can range
Symbols for important particles
Alpha 4/2He, Beta 0/-1e, positron 0/+1e, neutron 1/0n
Decay in equations
The particle is on the right side of the equation
Reasons for a nucleus to be unstable
The nucleus has too many protons compared to neutrons (positron decay)
The nucleus has too many neutrons compared to protons (beta decay)
The nucleus is too big (alpha decay)
Stable nucleus
N:p Ratio between 1 and 1.5
Radioactive dating
You can calculate the time needed to change from what is expected to what is actually found
Many substances can be radioactive and then followed as they move through the body
Fission reactors
Current nuclear reactors use fission reactions to produce heat which is used to turn water into steam and drive turbine engines that produce electricity
The sun and stars
Powered by nuclear fusion…this is related to the fact that the most abundant element in the universe is hydrogen…followed by helium
Means element can be split when bombarded by neutrons
Chain reaction
Each spitting nucleus can emit neutrons that can split other nuclei is the basis
Breeder reactors
Use different isotoprs
Fusion in the Sun
Involves several steps – 4(1/1H)–> 4/2He+2 0/1e+energy
Thermonuclear devices
Use isotopes of hydrogen (deuterium and tritium)
equation Basis for explaining where energy associated with nuclear changes comes from
Mass defect
When a nuclear change occurred, the mass of the products is slightly less than the mass of the reactants. The loss in mass is called the mass defect
Variables in mass defect equations
e= the energy
m=the mass defect
c= the speed of light, 3.000 c 10^8 m/s
1 kg of mass converted into energy
Equivalent to burning 3 billion kg of coal
During beta decay
1 neutron changes into 1 proton + 1 negative beta particle (the atomic # increases by one due to the new proton. The mass # is unchanged… A neutron is gone. To maintain electrical neutrality, a negative beta particle is also formed
During positron decay
1 proton changes into 1 neutron+1 positron particle (the atomic # decreases by one due to the loss of a proton. Since it changed into a neutron the mass # is unchanged)
Daughter isotope
Often unstable after decay, many decays may occur before stable nucleus is formed
Characteristic decay series
Method used to verify the identity of newly formed atoms
Nuclear waste problem
Daughter products can be even more radioactive than parent so disposal/storage is a problem
Useful characteristic of decay particle
Ionize the air as they pass through by striking atoms and knocking off electrons
Geiger counters
Detects and measures radiation by: radioactive particles pass through chamber with two electrodes, ionized particles migrate to + and – electrodes and complete the circuit
Smoke detectors
Use tiny piece of radioactive Am to keep circuit flowing due to ionized particles. Smoke particles attract ionized particles, break the circuit, and set off alarm
Kept ionized by tiny bits of radioactive material to more easily attract tiny bits of dust
Glenn Seaborg and Al Ghiorso
At UC Berjeley were able to use E.O. Lawrence’s cyclotron to make larger atoms (elements 93 and 94)
Largest naturally occurring element
Uranium Z=92
New element uses
Medical field, further understanding of nucleus
Largest element
As of July 2000, 118
Nuclear force
Force of attraction that holds nucleus together
Nuclear binding energy
Energy produced when atoms nucleons are bound together, energy released when a nucleus is formed from nucleons
Band of stability
Stable isotopes fall into a narrow band
Radioactive tracer/label
If you replace one atom with radioisotope- monitor radioactive emissions
Radiation therapy
Damage DNA of cancer cells
External beam radiation therapy
Delivered by machine
Internal radiation (brachytherapy)
Substance introduced to body
Nonionizing radiation
Light, microwaves
Categories: Nuclear Chemistry