nuclear chemistry. nuclear reactions chemical reactions what can not change in a chemical...
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Nuclear
Chemistry
Nuclear
Chemistry
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Nuclear ReactionsNuclear ReactionsNuclear ReactionsNuclear Reactions
Chemical reactions What can NOT change in a chemical
reaction?Nuclear Reactions: changes that occur in
the nucleus of an atom The nucleus is unstable!!
Most atoms have unstable nuclei.
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Why are some stable, while others Why are some stable, while others are not?are not?
Why are some stable, while others Why are some stable, while others are not?are not?
Primary Reason: ratio of the neutrons
to the protons (n/p) An atom is most stable
when ratio is 1:1 The maximum ratio of
stability is around 1.5 : 1
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RadioactivityRadioactivityRadioactivityRadioactivity
An unstable nucleus emits rays and particles, called radiation, to become stable The process is called
radioactivity Gain stability by
LOSING energy Discovery dealt a
deathblow to Dalton’s theory of indivisible atoms
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He42
Types of RadiationTypes of RadiationTypes of RadiationTypes of Radiation
Alpha particle () helium nucleus
paper2+
Beta particle (-) electron e0
-11-
leadGamma ()
high-energy photon0
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3 Radioactive Particles3 Radioactive Particles3 Radioactive Particles3 Radioactive Particles
1. Alpha Particle (+) It travels about 1/10 the speed of light
(slowest)
• It is the largest, most massive particle
It is the most dangerous if ingested It has the least penetrating ability -
paper can stop this particle
He42
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3 Radioactive Particles3 Radioactive Particles3 Radioactive Particles3 Radioactive Particles
2. Beta Particle (-) Fast accelerated electron Ejected when a neutron is converted to a
proton in the nucleus Travels 1/4 the speed of light. It is lighter and faster than the alpha
particle. Average penetrating ability - can be
stopped by heavy clothing
e0-1
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3 Radioactive Particles3 Radioactive Particles3 Radioactive Particles3 Radioactive Particles
3. Gamma Ray Not a particle; it is high energy
electromagnetic radiation Has no mass and no charge. Always accompanies either beta or alpha
radiation. Travels at the speed of light. Highest penetrating ability - can be stopped
by heavy shielding such as lead.
00
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Radioactive Particles Radioactive Particles SummarySummary
Radioactive Particles Radioactive Particles SummarySummary
Alpha Particle
Positive Charge
Mass of a
Helium nucleus
1/10 the speed of light
Beta particle
Negative Charge
Mass of an
electron
1/4 the speed of light
Gamma ray
No charge
No Mass
Speed of Light, c
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Nuclear DecayNuclear DecayNuclear DecayNuclear Decay
Alpha Emission
He Th U 42
23490
23892
parentnuclide
daughternuclide
alphaparticle
Numbers must balance!!
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Nuclear DecayNuclear DecayNuclear DecayNuclear Decay
Beta Emission
A neutron is converted in the nucleus of an atom
A new atom is formed whose atomic number is increased by 1
e Xe I 0-1
13154
13153
epn 01
11
10
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Nuclear DecayNuclear DecayNuclear DecayNuclear Decay
Gamma Emission Always accompanies alpha and beta
emissions.Transmutation
One element becomes another.
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Half-lifeHalf-lifeHalf-lifeHalf-life
Half-life (t½) Time required for half the atoms of a
radioactive nuclide to decay. Shorter half-life = less stable.
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So, what does this So, what does this mean?mean?
So, what does this So, what does this mean?mean?
Let’s say you have 100 g of radioactive C-14. The half-life of C-14 is 5730 years. How many grams are left after one half-
life? How many grams are left after two half-
lives?
50 g
25 g
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Common RadioisotopesCommon RadioisotopesCommon RadioisotopesCommon Radioisotopes
Isotope Half-Life Radiation Emitted
Carbon-14 5,730 years
Radon-222 3.8 days
Uranium-235 7.0 x 108 years
Uranium-238 4.46 x 109 years
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Half-lifeHalf-lifeHalf-lifeHalf-life
r (0.5)ni
r : final massi : initial massn : # of half-lives
To find the remaining amount…
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More Half-Life EquationsMore Half-Life EquationsMore Half-Life EquationsMore Half-Life Equations
Total time passed (p) = n x t1/2
To find the half-life t1/2 =
To find the # of half lives that have passed… n =
p
n
1/ 2
p
t
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Half-lifeHalf-lifeHalf-lifeHalf-life Fluorine-21 has a half-life of 5.0 seconds. If you
start with 25 g of fluorine-21, how many grams would remain after 60.0 s?
GIVEN:
t½ = 5.0 s
i = 25 g
r = ?
p = 60.0 s
n = 60.0s ÷ 5.0s =12
WORK:
r = i (0.5 )n
r = (25 g)(0.5)12
r = 0.0061 g
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You try it!You try it!You try it!You try it!
If the half life element A is 3 hours and you have 90 grams of it, how many grams would be left after 9 hours?
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FF issionissionFF issionission
splitting a nucleus into two or more smaller nuclei
1 g of 235U = 3 tons of coal
U23592
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FF issionissionFF issionission
chain reaction - self-propagating reaction
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FusionFusionFusionFusioncombining of two nuclei to form one nucleus of larger mass thermonuclear reaction – requires temp of 40,000,000 K to sustain1 g of fusion fuel =
20 tons of coaloccurs naturally in
stars
HH 31
21