Nuclear chemistry
Atomic Structure/Revision
Atoms consist of a nucleus, containing protons and neutrons and a
surrounding cloud of electrons.
Particle
Proton
Neutron
Electron
Symbol
or 11H
1
0n
0
-1e
1
1p
Approx. mass
1
1
1/2000
Charge
+1
0
-1
Atomic number =
number of protons
Mass number
number of protons + number of neutrons
=
=
Location
Nucleus
Nucleus
Orbital
number of electrons
(in uncharged atom)
All atoms except 11H (hydrogen) contain neutrons as well as protons in
their nuclei.
Atomic notation
Mass Number
y
Atomic Number
z
X – Symbol of Element
From this notation the number of protons, neutrons and electrons for a
neutral atom can be calculated.
Eg.
24
12Mg
Protons = 12
Electrons = 12
Neutrons = Mass number – Atomic number
= 24
12
= 12
Isotopes
Isotopes are different types of atoms of the same element. i.e. they have
the same atomic number but different mass number (they have the same
number of protons but a different number of neutrons).
Eg. Chlorine has two isotopes:
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17Cl
17 protons
17 electrons
18 neutrons
17Cl
17 protons
17 electrons
20 neutrons
1
Radioactivity
In radioactive decay, changes are taking place in the nuclei of the
radioactive isotopes (radioisotopes). ). The stability of the nucleus
depends on the ratio of neutrons to protons.
Radioactive elements emit radiation to allow the nucleus to become more
stable. There are 3 types of radiation – alpha(), beta() and gamma()
Radiation is affected by application of a magnetic or electrical field, the
three different types of radiation are deflected in different ways.
The nature and properties of radiation
Radiation
Alpha, α
Beta, β
Gamma, γ



Penetration
Few cm in air
Thin metal foil
Great thickness of
concrete
Nature
He nucleus
Electron
Electromagnetic
radiation
Symbol
4
2𝐻𝑒
0
−1𝑒
Charge
2+
1-
Mass
4
1/2000
None
None
None
Alpha radiation has the lowest energy and is the least penetrating.
Gamma radiation has the highest energy and is the most
penetrating.
Beta radiation falls between alpha and gamma radiation with
respect to energy and penetrating.
With all radioactive decay equations the sum of the mass numbers
and the sum of the atomic numbers must be the same.
Loss of an α particle
Loss of an α particle causes a loss of 2 units of charge and 4 units of
mass.
232
228
4
90𝑇ℎ
88𝑅𝑎 + 2𝐻𝑒
2
Loss of an β particle
The particles in β radiation are electrons. β particles are formed in the
nucleus when neutrons break up into protons and electrons.
1
0𝑛

1
1𝑝
+
0
−1𝑒
As soon as they form, these high-energy electrons are ejected from the
nucleus as beta radiation. (‘Normal’ electrons are low energy electrons
when compared to the β electron, which is ejected from the nucleus).
Loss of an β particle causes a gain of 1 unit of charge and no change in
mass.
228
0
 228
88𝑅𝑎
89𝐴𝑐 + −1𝑒
Loss of an γ particle
Gamma waves electromagnetic waves and do not affect the Atomic
number or mass number of the radioactive isotope.
Half-live calculations
A measure of how quickly a radioactive substances decays is called it’s
half life. Atomic nuclei are said to be unstable when they spontaneously
disintegrate. It is impossible to predict when a particular atom will
disintegrate. It is a random process.
The half life ( t1/2 ) of a radioactive isotope is the time taken for the
mass or activity of the isotope to halve its radioactive decay.
The half life is independent of mass, pressure, concentration
or the chemical state of the isotope
e.g.
The half life of
12.5g?
14
C is 5,730 years. How long would it take to decay to
100g of 14C would decay to 12.5g in 3 x t
i.e. 5,730 x 3 years = 17,190 yrs
1/2
,
3
The time it takes this radioactive isotope to
reduce its mass by a half is 100 s.
The half life is therefore 100 s.
Uses of radioisotopes
Many artificially produced radioisotopes are known, these radioisotopes
have wide ranging applications in both medical and industrial fields.
Medical radioisotopes have been used for a considerable time for the
treatment of various cancers.



The alpha emitter 60
27𝐶𝑜 is used to treat deep-seated tumours.
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The beta emitter 15𝑃 is used to treat skin cancer.
The short half-life beta emitter 131
53𝐼 is used to assess the thyroid
gland (which absorbs iodine).
Industrial radioisotopes include:


The gamma emitter 60
27𝐶𝑜 is used to check the condition of welds
and to irradiate food, killing bacteria and fungi.
The alpha emitter 241
95𝐴𝑚 is used in domestic smoke alarms.
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Radioisotopes in scientific research include:


32
15𝑃 is
14
6𝐶 is
used to trace uptake of phosphate fertiliser in plants
used to date archaeological specimens of organic origin.
The origin of the elements
There are large quantities of hydrogen in space but most is widely
separated and unlikely to come into contact. However, the regions
between stars (interstellar gas clouds) contain more concentrated
hydrogen. Fusion occurs in these interstellar gas clouds to form larger
nuclei coalescing the gases into dense clumps and thus forming stars. Vast
amounts of energy are produced which initiates more fusion.
Eg.
3 42𝐻𝑒  126𝐶
12
4
6𝐶 + 2𝐻𝑒 
16
8𝑂
All elements have been produced by fusion, with heavier, hotter and
denser stars producing the heavier elements, essentially from hydrogen.
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