1 nuclear chemistry why do some atoms undergo nuclear changes?
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NUCLEAR CHEMISTRY
Why do some atoms undergo nuclear
changes?
2ATOMIC COMPOSITIONATOMIC COMPOSITION
• ProtonsProtons– + electrical charge+ electrical charge– mass = 1.672623 x 10mass = 1.672623 x 10-24-24 g g– relative mass = 1.007 atomic mass units relative mass = 1.007 atomic mass units
(amu)(amu)• ElectronsElectrons
– negative electrical chargenegative electrical charge– relative mass = 0.0005 amurelative mass = 0.0005 amu
• NeutronsNeutrons– no electrical chargeno electrical charge– mass = 1.009 amumass = 1.009 amu
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RadioactivityRadioactivity• One of the pieces of evidence for the One of the pieces of evidence for the
fact that atoms are made of smaller fact that atoms are made of smaller particles came from the work of particles came from the work of
Marie CurieMarie Curie (1876-1934). (1876-1934). • She discovered She discovered radioactivityradioactivity, ,
the spontaneous disintegration of the spontaneous disintegration of some elements into smaller pieces.some elements into smaller pieces.
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RadioactivityRadioactivity Emission of particles and/or
energy due to a change in the nucleus of an atom.
Nuclear Radiation also called Ionizing radiation
Measure with Geiger Counter
5Geiger Counter: Geiger Counter:
Radiation detectionRadiation detection
6IsotopesIsotopes• Hydrogen:
– 11H, protium
– 21H, deuterium
– 31H, tritium
(radioactive)
• Helium, 42He
• Lithium, 63Li
and 73Li
• Boron, 105B
and 115B
• Except for 11H the mass
number is always at least 2
x atomic number.
• Repulsive forces between
protons must be
moderated by neutrons.
7IsotopesIsotopes
• Same element (Same element (ZZ) but different mass ) but different mass number (number (AA).).
• Boron-10Boron-10 has has 5 p5 p and 5 n: and 5 n: 101055BB
• Boron-11Boron-11 has has 5 p5 p and 6 n: and 6 n: 111155BB
10B
11B
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Why do unstable isotopes undergo nuclear reactions?
Unstable isotopes undergo nuclear reactions so that they may be changed, or
transformed, into stable isotopes.
9Stability Stability of of NucleiNuclei
• Heaviest naturally Heaviest naturally
occurring non-radioactive occurring non-radioactive
isotope is isotope is 209209Bi with 83 Bi with 83
protons and 126 neutronsprotons and 126 neutrons
• There are 83 x 126 = There are 83 x 126 =
10,458 possible isotopes. 10,458 possible isotopes.
Why so few actually exist?Why so few actually exist?
10Band of Stability Band of Stability and Radioactive and Radioactive DecayDecay
Isotopes with a n/p ratio, below or
above the band of stability decay, by
various nuclear reactions.
11Stability Stability of of NucleiNuclei
• Out of > 300 stable isotopes:
EvenEven OddOdd
OddOdd
EvenEven
ZZNN
157157 5252
5050 55
31311515PP
191999FF
2211H, H, 66
33Li, Li, 101055B, B, 1414
77N, N, 1801807373TaTa
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Types of RadiationTypes of Radiation
Types of Radiation
What are three types of nuclear radiation?
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Types of RadiationTypes of Radiation
Radiation is emitted during radioactive decay.
Three types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation.
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Types of NUCLEAR Types of NUCLEAR RadiationRadiation
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Types of RadiationTypes of RadiationAlpha Radiation
Some radioactive sources emit helium nuclei, which are also called alpha particles.
• Each alpha particle contains two protons and two neutrons and has a double positive charge.
• An alpha particle is written He or .42
– The electric charge is usually omitted.
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Alpha Radiation
The radioisotope uranium-238 emits alpha radiation and is transformed into another
radioisotope, thorium-234.
U23892
Uranium-238
Th +23490
Thorium-234
He ( emission)42
Alpha particle
Radioactivedecay
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Alpha Radiation
When an atom loses an alpha particle, the atomic number of the product is lowered by two and its mass number is lowered by four.
• In a balanced nuclear equation, the sum of the mass numbers (superscripts) on the right must equal the sum on the left.
• The same is true for the atomic numbers (subscripts).
U23892 Th +234
90 He42→
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Alpha Radiation
Because of their large mass and charge, alpha particles do not travel very far and are not
very penetrating.
• A sheet of paper or the surface of your skin can stop them.
– But radioisotopes that emit alpha particles can cause harm when ingested.
– Once inside the body, the particles don’t have to travel far to penetrate soft tissue.
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Beta Radiation
An electron resulting from the breaking apart of a neutron in an atom is called a
beta particle.
• The neutron breaks apart into a proton, which remains in the nucleus, and a fast-moving electron, which is released.
n10
Neutron
p +11
Proton
e 0–1
Electron(beta particle)
→
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Beta Radiation
• The –1 represents the charge on the electron.
• The 0 represents the extremely small mass of the electron compared to the mass of a
proton.
n10
Neutron
p +11
Proton
e 0–1
Electron(beta particle)
→
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Beta Radiation
• The nitrogen-14 atom has the same mass number as carbon-14, but its atomic number has increased by 1.
• It contains an additional proton and one fewer neutron.
C146
Carbon-14 (radioactive)
N +147
Nitrogen-14 (stable)
e ( emission)0–1
Beta particle
→
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Beta Radiation
A beta particle has less charge than an alpha particle and much less mass than an alpha
particle.
• Thus, beta particles are more penetrating than alpha particles.
– Beta particles can pass through paper but are stopped by aluminum foil or thin pieces of
wood.
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Beta Radiation
Because of their opposite charges, alpha and beta radiation can be separated by an electric field.
• Alpha particles move toward the negative plate.
• Beta particles move toward the positive plate.
• Gamma rays are not deflected.
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Gamma Radiation
A high-energy photon emitted by a radioisotope is called a gamma ray.
• The high-energy photons are a form of electromagnetic radiation.
• Gamma rays are emitted during radioactive decay.
Ra +22688
Radium-226
Th23090
Thorium-230
He + 42
Alpha particle
Gamma ray
→
Pa +23491
Protactinium-234
Th23490
Thorium-234
e + 0–1
Beta particle
Gamma ray
→
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Types of RadiationTypes of Radiation
Gamma rays have no mass and no electrical charge.
• Emission of gamma radiation does not alter the atomic number or mass number of an atom.
Gamma Radiation
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Gamma rays are extremely penetrating making them dangerous.
• Gamma rays pass easily through paper, wood, and the human body.• They can be stopped, although not completely, by several meters of
concrete or several centimeters of lead.
Gamma Radiation
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Penetrating AbilityPenetrating Ability
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Gamma rays can be dangerous because of their penetrating power. What property determines the relative penetrating power of electromagnetic radiation?
CHEMISTRY & YOUCHEMISTRY & YOU
The wavelength and energy of electromagnetic radiation determine its relative penetrating power. Gamma rays have a shorter wavelength and higher energy than X-rays or visible light.
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Characteristics of Some Types of Radiation
Type Consists of Symbol ChargeMass (amu)
Common source
Penetrating power
Alpha radiation
Alpha particles (helium nuclei)
, 2+ 4Radium-226
Low (0.05 mm body tissue)
Beta radiation
Beta particles (electrons)
, 1– 1/1837Carbon-14
Moderate (4 mm body tissue)
Gamma radiation
High-energy electromagnetic radiation
0 0 Cobalt-60Very high (penetrates body easily)
He42
e0–1
Interpret DataInterpret Data
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Which process involves a radioactive nucleus releasing a high-speed electron?
A. oxidation
B. alpha emission
C. beta emission
D. gamma radiation
C
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RadioactivityRadioactivity
How do nuclear reactions differ from chemical reactions?
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RadioactivityRadioactivity
Unlike chemical reactions, nuclear reactions are NOT
affected by changes in temperature, pressure, or the
presence of catalysts.
Nuclear reactions of a given radioisotope cannot be slowed
down, sped up, or stopped.
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Nuclear ReactionsNuclear Reactions
• Ernest Rutherford found Ra forms Rn gas
when emitting an alpha particle.
• 1902—Rutherford and Soddy proposed
radioactivity is the result of the natural
change of the isotope of one element into
an isotope of a different element.
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Nuclear ReactionsNuclear ReactionsorTransmutationsorTransmutationsNatural Decay
Spontaneous breakdown of unstable nuclei.
Called Radioisotopes
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NATURAL Decay:NATURAL Decay:
DECAY = Fall apartAlpha DECAYBeta DECAY
Positon DECAY
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RadioactivityRadioactivity
Radioactive decay is a spontaneous process that does not require an input of energy.
• If the product of a nuclear reaction is unstable, it will decay too.
• The process continues until unstable isotopes of one element are changed, into
stable isotopes of a different element.
• Stable isotopes are not radioactive.
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Nuclear ReactionsNuclear Reactions• Alpha emissionAlpha emission
Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2.
Nucleons are rearranged but conserved
Nucleons = PROTON OR NEUTRON (particle in the nucleus)
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Nuclear ReactionsNuclear Reactions• Beta emissionBeta emission
Note that mass number (A) is unchanged and atomic number (Z) goes up by 1.
How does this happen?
39Other Types of Nuclear Other Types of Nuclear ReactionsReactions
Positron (Positron (00+1+1): a positive electron): a positive electron
K-capture:K-capture: the capture of an electron from the first or K shell
An electron and proton combine to form a neutron.0
-1e + 11p --> 1
0n
207 207
40Radioactive Decay SeriesRadioactive Decay Series
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Writing Nuclear Reactions Parent element = Reactant
Daughter element = Product
Radioactivity = radiation produced
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Writing Nuclear Reactions
Law of Conservation of Mass
L. of C. of Charge Isotopic Notation Mass # and Nuclear Charge
146C = 14
7N + 0-1e
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Key ConceptsKey Concepts
Unlike chemical reactions, nuclear reactions are not affected by changes in temperature, pressure, or the presence of catalysts. Also, nuclear reactions of a given radioisotope cannot be slowed down, sped up, or stopped.
Three types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation.