nuclear chemistry edited

8/12/2019 Nuclear Chemistry Edited

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Gold foil experiment This was performed by Rutherford and his colleagues, Ernest

,greiger

He used an energetic alpha particle and fired them through a and they were deflected as they were passed through the gold

He observed that most particles were deflected by a small angfound that large deflections were there for the particles thaclose to the nucleus and got deflected by large angles.

He concluded that the positive charge of the atom must be cothe centre of the atom.

He concluded that the size of the nucleus must be smaller thaby a factor of 10^4.

He finally concluded that most of the atom is an empty space


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Nuclear structure

They consists of protons and neutrons.they are bind togetherstrong force called nuclear force. this force is of short range equal to 10-15 m .this means the attractive force between nupairs drops to zero for nucleon separations greater than certacritical value.

In lighter nucleus the no.of protons is equal to no.of neutronshence we get a stable nuclei with only nuclear force acting asoperating force.

whereas in heavier atoms we have more neutrons in comparprotons .this results in coloumbic repulsion effect.this is becanucleon will interact with only a small number of its neighbouthrough that force and the energy tied up with strong bondincreases. also the energy tied up in columbic bond increasesprotons start interacting with other protons in the system.


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Subatomic particles

In order to understand the structure we need to know some particles lleptons, mesons and baryons .

leptons are the lightest particles including the electron(mec^2=0.511Mev).they only interact with weak electromagnetic interactions. they hinternal structure and are not composed of other small particles. they true fundamental particles with no finite dimensions .they all have a sp.eg:electrons,tau particles and their respective neutrinos.

Mesons they are the intermediate perticles having mc^2=140 Mev . strongly interacting particles having an integral spin.they decay throug

strong ,weak,electromagnetic interactions .eg :pions ,hadrons. they coof one quark and antiquark bound together by strong interaction.

Baryons are the heaviest of all particles having e=450 Mev .they arestrongly interacting having half integral spins(1/2, 3/2, 5/2).the familmembers are neutrons and protons. A baryon is made up of three qua


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Nuclear spin and magnetism

Nuclei like atoms have an intrinsic angular momentwhose


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What are quarks?

A quark is an elementary particle and a fundamental constituent of maquarks are never found in isolation they are only found within hadronsbaryons or mesons.

They are actually six types of quarks . they are strange, up, down, chabottom .up and down quarks have the lowest masses of all quarks. thequarks change into up and down quarks through particle decay. becautheir stability they are found in most abundant in the universe.

Every quark has an antiquark also which is opposite in sign and equal magnitude.

Its difficult to isolate a quark as it might take perhaps infinite energy tseparate them even to a distance of a nucleon.actually when we try tseparate two quarks they form a quark and antiquark pair which thencombines to form a meson.paradoxically inside a nucleon or meson a qexist as a free particle and the force between two quarks inside a nucapproaches almost zero.


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Quark model

It was suggested independently by murray gellmann and george zweigsubatomic particles like mesons and baryons are composed of more sefundamental particles called quarks.

The quarks listed at that time were up(u),down(d),strange (s) along wantiparticles i.e the antiquarks ,,.

The quarks have fractional electric charges (equal to elementary chargelectron) i.e +2/3 for the u quark,-1/3 for the d and s quark.

The quarks have fractional baryon number i.e 1/3. every baryon has b

number equal to B=1(baryons),B=-1(antibaryons),B=0(non baryons). All quarks have a spin value of which means according to quantum

mechanics combination of two quarks can have either have a spin valuor 1.

According to this model baryons are composed of three quarks while mare made up of two quarks.


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Reactions of the nucleus Alpha decay it is the radioactive decay of the nucle

which alpha particles and other particles are emitted fthe nucleus.

Beta decay - a nucleus that decays spontaneously byemitting an electron(positive or negative ) is said toundergo beta decay.

Gamma decay this occurs after the ,decay when tdaughter nucleus is in an excited state . It can then ma lower energy state by emitting a gamma ray photonthe same way that an atomic electron can jump to a lenergy state by emitting a light ray photon.


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radioactivity

Radiation was first discovered by Henri Becquerrel he found that the piece of uranium he was workinghad a special property of turning his photographicinto black.

It was pierre and marie curie who isolated radioact

elements and discussed radioactivity significantly. Radioactivity is the process by which an unstable a

or nucleus loses energy by emitting particles of ionradiation.the kind of emmissions are ,,decay.


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Alpha decay

Alpha decay, or-decay, is a type of radioactive decayin which an atomic nucleu

an alphaparticleand thereby transforms (or 'decays') intoan atom with a mass nuless and atomic number2 less. For example, uranium-238decaying through -partemission to form thorium-234can be expressed as

Because an alpha particleis the same as the nucleus of a helium-4atom - consistintwo protonsand two neutronsand thus having mass number4 and atomic numbercan also be written as:

Notice how, on either side of the nuclear equation, both the mass number and the number are conserved: the mass number is 238 on the right side and (234 + 4) onside, and the atomic number is 92 on the right side and (90 + 2) on the left side.

The alpha particle also has a charge +2, but the charge is usually not written in nucequations, which describe nuclear reactions without considering the electrons. Thisconvention is not meant to imply that the nuclei necessarily occur in neutral atomsdecay typically occurs in the heaviest nuclides. In theory it can occur only in nucleisomewhat heavier than nickel (element 28), where overall binding energyper nucllonger a minimum, and the nuclides are therefore unstable toward spontaneous fisprocesses. In practice, this mode of decay has only been observed in nuclides consheavier than nickel, with the lightest known alpha emitter being the lightest isotopnumbers 106110) of tellurium(element 52)
http://en.wikipedia.org/wiki/Alpha_particlehttp://en.wikipedia.org/wiki/Alpha_particlehttp://en.wikipedia.org/wiki/Radioactivityhttp://en.wikipedia.org/wiki/Atomic_nucleushttp://en.wikipedia.org/wiki/Mass_numberhttp://en.wikipedia.org/wiki/Alpha_particlehttp://en.wikipedia.org/wiki/Atomic_numberhttp://en.wikipedia.org/wiki/Atomic_numberhttp://en.wikipedia.org/wiki/Uranium-238http://en.wikipedia.org/wiki/Mass_numberhttp://en.wikipedia.org/wiki/Atomic_numberhttp://en.wikipedia.org/wiki/Thorium-234http://en.wikipedia.org/wiki/Thorium-234http://en.wikipedia.org/wiki/Uranium-238http://en.wikipedia.org/wiki/Thorium-234http://en.wikipedia.org/wiki/Protonhttp://en.wikipedia.org/wiki/Alpha_particlehttp://en.wikipedia.org/wiki/Neutronshttp://en.wikipedia.org/wiki/Neutronshttp://en.wikipedia.org/wiki/Mass_numberhttp://en.wikipedia.org/wiki/Mass_numberhttp://en.wikipedia.org/wiki/Helium-4http://en.wikipedia.org/wiki/Atomic_numberhttp://en.wikipedia.org/wiki/Protonhttp://en.wikipedia.org/wiki/Neutronshttp://en.wikipedia.org/wiki/Mass_numberhttp://en.wikipedia.org/wiki/Atomic_numberhttp://en.wikipedia.org/wiki/Binding_energyhttp://en.wikipedia.org/wiki/Binding_energyhttp://en.wikipedia.org/wiki/Isotopehttp://en.wikipedia.org/wiki/Telluriumhttp://en.wikipedia.org/wiki/Isotopehttp://en.wikipedia.org/wiki/Telluriumhttp://en.wikipedia.org/wiki/Telluriumhttp://en.wikipedia.org/wiki/Isotopehttp://en.wikipedia.org/wiki/Binding_energyhttp://en.wikipedia.org/wiki/Atomic_numberhttp://en.wikipedia.org/wiki/Mass_numberhttp://en.wikipedia.org/wiki/Neutronshttp://en.wikipedia.org/wiki/Protonhttp://en.wikipedia.org/wiki/Helium-4http://en.wikipedia.org/wiki/Helium-4http://en.wikipedia.org/wiki/Helium-4http://en.wikipedia.org/wiki/Alpha_particlehttp://en.wikipedia.org/wiki/Thorium-234http://en.wikipedia.org/wiki/Thorium-234http://en.wikipedia.org/wiki/Thorium-234http://en.wikipedia.org/wiki/Uranium-238http://en.wikipedia.org/wiki/Uranium-238http://en.wikipedia.org/wiki/Uranium-238http://en.wikipedia.org/wiki/Atomic_numberhttp://en.wikipedia.org/wiki/Mass_numberhttp://en.wikipedia.org/wiki/Alpha_particlehttp://en.wikipedia.org/wiki/Atomic_nucleushttp://en.wikipedia.org/wiki/Radioactivity


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Beta decayIn this decay electrons are emitted as particles .there are two of decay : negative decay and positive decay.

1.In positive decay ,a positron is emitted which is an antiparticelectron. in this a proton decays into a neutron and a positroneutrino is released for conservation of momentum. The reac

Pn+ 1+

2.In negative decay a neutron decays into an electron and becinto a proton.it also releases an antineutrino. the reaction of

undergoing decay to give scandium is 20Ca-1+ S


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Nuclear models

1. The collective model: this model wsa developed by Neils Boexplain nuclear fission. here nucleus is treated as a bodyanalogous to a oil drop.in this the equilibrium shape of the drop is determined by the interactions of its molecules andsimilarly the equilibrium shape of the nucleus is determinedinteraction among its nucleons. a nucleus can absorb energthe entire nucleus rotating about its axis or vibrating along equilibrium shape.the expression of the energy is given by

2. The independent particle model :it states that each nucleonassigned well defined states similar to the states of electronatom .like electrons ,nucleons arrange themselves into shewell defined quantum numbers. when a shell is filled the nuobtained is of unusually high stability.


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scope in this field

Nuclear fiission and fusion


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Summary

nuclear chemistry edited

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