CHEM 121 FINAL EXAM | UPDATED QUESTIONS AND ANSWERS UPDATED .Buy Quality Materials!
0 view 0 purchase
Course
CHEM 121
Institution
CHEM 121
CHEM 121 FINAL EXAM | UPDATED QUESTIONS AND ANSWERS UPDATED .Buy Quality Materials!
Radioactivity
Becquerel (1896) discovered that photographic plates darkened in contact with uranium ore
Rutherford discovered two types of particles
alpha and beta
alpha, a, particle
particles: heavy, non-...
CHEM 121 FINAL EXAM | UPDATED QUESTIONS AND
ANSWERS UPDATED .Buy Quality Materials!
Radioactivity
Becquerel (1896) discovered that photographic plates darkened in contact with uranium
ore
Rutherford discovered two types of particles
alpha and beta
alpha, a, particle
particles: heavy, non-penetrating, He 2+ (He nucleus, 2protons and 2 neutrons)
beta, b particles
lighter, more penetrating, e-
Villard
y rays: electromagnetic radiation, very energetic and penetrating
nuclear reactions
Nucleus transforms to another by emission or absorption of radio active particles.
Sum of mass and sum of atomic numbers must be equal in
products and reactants
Ejection of electron from
nucleus
Ejection of gamma rays
Nuclear reaction results in nuclei in an excited state
Relaxation to ground state by emitting radiation as gamma ray
decay series
Parent is the reactant
Daughter is the product (daughter my also decay)
Uranium decay series makes possible dating of objects too old for
carbon-14dating.
Longer half-lives.
radon is produced
Decays to 218Po which causes lung cancer.
Home testing is important in regions with high uranium in the soil
Minimized by ventilation
Positron
positron (antimatter)—anti electron: same mass as electron but opposite charge
electron capture
Electron is captured by the nucleus
Electron has very small mass so mass number is unchanged and atomic number
reduced by 1.
stability of nuclei
Very few stable isotopes exist
Band of stability: narrow range of stability
Only two isotopes exist with more protons than neutrons ( 2 H, and 3 He)
Up to Ca, stable isotopes often have equal protons and neutrons
,Beyond Ca, stable isotopes always have more neutrons than protons
Beyond Bi, no isotopes are stable
Heavy nuclei are unstable
As nuclei get heavier, lifetimes are shorter
Even numbers of atomic number are more stable than odd
Neutron rich means
high N/Z
b decay, neutrons to proton
mass number much higher than atomic mass
proton rich means
low N/Z ratio, B + emission, e capture, proton to neutron, mass number much lower
Eb nuclear binding energy
Energy associated with formation of the nucleus.
Holds nucleus together
Large to overcome the repulsion of the protons.
mass defect
Mass of nucleus is less than sum of masses of neutrons and protons
Matter transformed to binding energy
E = mc2
1 mole protons + 1 moles neutrons =
1 mole of nuclei + energy of 73 tons of TNT!
1st order kinetics
Half life (t½ ): time required to decay to half concentration (activity for radioactivity)
half life =
0.693/ke
acvivity
is number of nuclear disintegrations per unit time
Measured with Gieger counter
date with rate decay
Radiocarbon dating: 14 C (beta emitter) half life =5730 years (14 disintegrations/min)
Plants absorb CO2 into tissue continually ( 14 C is produced from solar radiation acting
on 14 N in upper atmosphere)
Carbon-14 percentage is same in the body as in the atmosphere
At death, the uptake stops but decay continues
Measuring amount of carbon-14 in object and comparing to atmosphere (at time of
death) gives age
limits of rate decay dating
Limited to 40K years (sample radioactivity decreases almost to 0)
Accuracy limited to 100 yrs
Carbon-14 in atmosphere varies (must be known for technique to be valid)
Uranium-238 is similar, comparing Pb to U
NUclear fision
Splitting of nuclei (into heavy nuclei)
More neutrons are ejected than used to initiate
Chain reaction Initiation: absorption of neutron
Propagation: recurring (released neutrons cause additional reactions which produce
, more neutrons)
Termination: process which consumes all fission able material or (more likely) neutrons
are captured but don't cause fission
alpha emmision
change in z = -2
change in a = -4
on product side 4/2 He
beta emmission
change in Z = +1
change in A = 0
on product side 0/-1 e
positron emission
change in Z = -1
Change in A = 0
on product side 0/1 e
electron capture
change in z = -1
change in a = 0
on reactant side 0/-1 e
on product side 0/0 y
proton
1/1 H
neutron
1/0 n
electron
0/-1 e
positron
0/1 e
alpha particle
4/2 He
Oxidation-Reduction (Redox) reactions
Essential for bodily function: food is oxidized, photosynthesis
Batteries: oxidation is separated from reduction
Electrons flow through wire
Fuel cells: hydrogen or methanol is oxidized
Principles of redox
One reactant is oxidized and another is reduced
Oxidation and reduction must balance (electrons are transferred and can't be destroyed)
Oxidizing agent causes oxidation and is reduced
Reducing agent causes reduction and is oxidized
Redox reactions cause a change in oxidation number
Oxidation
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller SUPERGRADES01. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $10.99. You're not tied to anything after your purchase.
