Transcript Nuclear Reactions

Nuclear
Chemistry
Types of
Radioactivity
What is radioactivity?
• The emission of
high energy
particles from the
nucleus of an
atom.
What are some sources of
Radioactivity?
Can you see radioactivity?
Hear?
Taste?
Feel?
Smell?
How did man find out about it?
• 1896 - Henri Becquerel accidentally left
some uranium salt in a drawer with a
photographic plate
– developed film showed an outline of the
uranium salt on the film.
– concluded an invisible energy
that exposed the film.
– This is called radiation.
How did man find out about it?
Becquerel's
photographic plate.
In the exposure at the
bottom of the image,
he has found that he
could absorb the
radiations, casting the
shadow of a Maltese
cross that was placed
between the plate and
the uranium salts.
Radioactive Elements
• Radioactive elements all have high atomic
numbers
– Remember: The atomic number
represents the number of protons in the
nucleus
• The number of protons determines what
the element is.
• Nucleus is held together by “strong force”
Remember this….
Radioactive Elements
• Larger atoms – harder to hold together
• This makes it possible for particles to
escape the nucleus
• This is radioactive decay
• Any element that has
an atomic number
greater than 83,
is radioactive.
Nuclear Notation
Isotopes of elements
• differ in their number of neutrons
in the nucleus
• This gives them a different atomic
mass.
• The nucleus of an isotope with a
certain atomic number and mass
is called a nuclide.
• Radiation energy is given off from
unstable (large) nuclides.
– Radioactive decay
Isotopes of elements
• Isotopes of elements differ in the ratio
of neutrons to protons.
– This ratio affects the stability of the nucleus
• In smaller atoms the nucleus is stable if
the ratio is 1 to 1
• In larger atoms the nucleus is stable if the
ratio is 3 neutrons to 2 protons
• An atom can be unstable if it has too few
or too many neutrons.
Chemical reactions
involve changes in the
number or
configuration of
electrons.
Nuclear reactions
involve the protons
and neutrons found
in the nucleus.
Nuclear Reactions
• During nuclear reactions, a nucleus can
lose or gain protons and neutrons
• Remember: adding or taking away protons
changes the identity of the element
An
alchemist’s
dream!!
Radioactive Decay
The release of radiation
Radioactive Decay
There are 3 types of radiation.
Alpha α Decay
• Alpha particles are given off when a
nucleus releases 2 protons and 2 neutrons
Alpha α Decay
• Alpha particle is the same as the nucleus
of a Helium atom
• Has a 2+ charge and an atomic mass of 4
• Is the largest and slowest form of radiation
• It is the least penetrating
– Can be stopped by a sheet of paper
• But still can be deadly
Alpha α Decay
Alpha decay follows the form:
Alpha α Decay
Ra

4
2
Po

4
2

4
2
222
88
208
84
256
103
Lr
He
He
He
+
218
86
Rn
+
204
82
Pb
+
252
101
Md
Beta β Decay
• Beta particles are electrons escaping from
the nucleus of an atom.
• Created by the spontaneous break down
of a neutron to a proton and an electron.
• Beta particles are faster and more
penetrating than Alpha particles
• Can be stopped by a sheet of aluminum
foil.
Beta β Decay
• Carbon-14 is an example of an isotope
that decays by beta emission
Beta β Decay
Beta negative decay follows the form:
Beta β Decay
90
38
Sr
239
93
247
95

0
1
e
+
Np

0
1
Am

0
1
e +
e +
90
39
Y
239
94
Pu
247
96
Cm
Gamma γ Waves
• have very high frequency, short
wavelengths
• have no mass and no charge.
• Travel at the speed of light.
• Usually released along with Beta or
Alpha particles.
• The most penetrating form of radiation
• Lead and concrete are used as barriers
for gamma waves.
• Can cause great harm to living cells
Gamma γ Waves
Gamma decay follows the form:
Electromagnetic radiation
Alpha, Beta, Gamma