Transcript Nuclear Chemistry

Atoms consist of
three basic particles:
•Protons (Positive)
•Neutrons (Neutral)
•Electrons (Negative)
The protons and
neutrons are located
in the nucleus.
 The electrons orbit
the nucleus.

9P
10 N
electrons
Fluorine
Protons and Neutrons are
particles called nucleons.
Protons and neutrons
have nearly the same
mass.
Nucleons have a mass
nearly 2000 times that
of electrons!!!
The positive protons
attract the negative
electrons and hold
them in orbit around
the nucleus.
 Atoms are generally
electrically neutral.

Why?
9P
Fluorine
Atoms are generally
neutral because the
number of positive
protons equals the
number of negative
electrons.
9P
Fluorine

6P
Carbon
The configuration of
electrons in an atom’s
highest energy level
determine its
chemical properties,
and thus its bonding
properties and
conductivity.
Isotopes are atoms of an
element that have the same
number of protons and
electrons, but different
numbers of neutrons.
 In other words, the number of
neutrons varies among the
atoms of that element.

The atomic mass found on the
periodic table is an average
mass of all the atoms of that
element, taking into account
the varying numbers of
neutrons.
 Neutrons do not play a role in
determining the identity of an
atom.


Hydrogen isotopes may
consist of one proton; one
proton plus one neutron; or
one proton plus two neutrons
Thus the Average Atomic Mass of
Hydrogen is 1.00794 amu.
Isotopes of
Hydrogen
The positive protons tend to repel
each other through electrostatic
repulsion.
But the presence of the neutrons
provides a ‘nuclear force’, or strong
force which holds the nucleus
together and stabilizes it.
Neutron
Proton
 The
nuclear force is only strong when
the nucleons are close together.
 As the number of protons increases,
the electrostatic repulsion increases
and the nuclear force weakens.
 So, even more neutrons are needed to
stabilize the nucleus.
A stable neutron - proton ratio is 1:1.
As the number of protons increases, so
does the number of neutrons. This
keeps the nucleus stable.
But, this increases the neutron – proton
ratio.
A neutron-proton ratio of 1.5 : 1 is
at the limit of stability.
•Atoms with more than 83 protons cannot
reach stability even with their larger numbers
of neutrons.
•All elements beyond bismuth on the
periodic table are unstable
and undergo some sort
of ‘decay’ in order to
become stable.
Unstable nuclei are those with a high
neutron:proton ratio; this will result in
decay or a change in the nucleus in order
to become stable.
 Transmutation: a change in the identity of
an element as a result
of a change in the
number of protons.


Atoms will decay by ejecting nucleons, or
altering the nucleons into different
particles by releasing one or more of the
following:
› Alpha rays
› Beta rays
› Gamma rays
› Positron Emission
› Electron Capture
Alpha particles consist of two
protons and two neutrons, and
are emitted during some kinds
of radioactive decay.
 Remember that protons
determine the identity of the
element : if an alpha particle is
emitted, the identity of the
element changes.
 Alpha particles are often called
a helium nucleus.

Helium nucleus
2+ charge
The atomic
number will be
reduced by
two, and the
mass number
reduced by
four.
Alpha rays are streams of alpha particles
given off during nuclear decay.
 Alpha rays are relatively slow and easy to
stop – a piece of paper will stop alpha
particles.

› They will travel only a few centimeters before
stopping even if they do not encounter any
matter.
› The positive charge of the alpha particle
attracts electrons nearby and the particle
becomes a harmless helium atom.
A Beta particle is an electron created and
emitted when a neutron is transformed* into
a proton and an electron during radioactive
decay.
 This action adds a proton and thus changes
the identity of the atom.
 The mass number stays
the same.

*The proton and electron
are not ‘inside’ the neutron.
They are created at the
time of the action.
Beta rays travel faster than alpha rays
and can penetrate paper, but are
generally stopped by thin sheets of metal
such as aluminum.
 Their negative charge causes them to
interact with other atoms which slows
their speed.

-
Gamma rays are photons of
electromagnetic radiation
with high frequency and
energy.
 Gamma rays are given off
when the nucleons undergo
an abrupt energy difference.
 Gamma rays have no mass –
they are pure energy.

Because they have no charge and are
high energy, gamma rays travel far and
penetrate further than alpha or beta rays.
 Thick concrete or lead is needed to stop
gamma rays.

The release of gamma rays alone do not
affect the identity of the atom since they
have no mass and no charge.
 But, gamma radiation may be released
along with release of an alpha or beta
particle.

Beta Particle
Gamma Ray
A positron is a particle that has the same
mass as that of an electron, but has a
positive charge.
A positron is emitted from the nucleus as
a proton is converted into a neutron.
The atomic number decreases by one but
the mass number stays the same.
1
p
1
1
n
0
0
B
+1
Positron
The nucleus can ‘capture’ one of its own innerorbital electrons if the atom is unstable due to
too many protons.
The electron will combine with a proton in the
nucleus and form a neutron.
The atomic number decreases by one but the
mass number stays the same.
0
-1
e
1
1
p
1
0
n
We are exposed to low doses of radiation,
including gamma radiation, every day
without ill effects.
•Radioactive decay heats the
interior of Earth.
•Radiation occurs in all of our
surroundings: air, water, soil.
•Cosmic radiation reaches us
every day.
The largest dose of
radiation we are
normally exposed to
comes from radon
gas which emanates
from the ground.
In low doses with short
exposure, gamma
radiation is not harmful.
But if you are exposed to
a high concentration, or
for an extended period of
time, gamma radiation
may cause damage.
Gamma rays are the most dangerous
form of radiation to humans because the
rays can travel through the body,
exposing organs to damage by altering
the molecules that make-up the body.
 This molecular damage can result in
genetic mutations, tumors, and other
physical abnormalities.

High-dose exposure may result
in radiation burns, nausea,
hair-loss, pre-mature aging,
weakness, organ damage, and
death within hours or a few
months, depending on the
dose.
Humans have the ability to harness and
manipulate radioactivity for:
› National defense and weaponry
› Medical diagnosis and treatments
› Energy production
› Radioactive Dating
Nuclear weaponry includes the
nuclear bomb – the explosive
energy coming from nuclear
reactions, usually fission, but
sometimes the combinations of
fission and fusion.
Atomic bomb: fission bomb
Hydrogen bomb:
thermonuclear bomb (uses
fusion and fission)
Naval vessels are equipped to
use nuclear propulsion.
Nuclear warheads attached
to missiles can be launched
if needed for national
defense.
Gamma radiation can be
safely used when directed
at cancerous tumors for
the purpose of killing
cancer cells.
 Gamma rays are used in
the medical field for
imaging purposes to
diagnose diseases and
tumors.

The nuclear fission reaction is used in power
plants to generate electricity for homes and
industry.
Nuclear power plants supplied
roughly 13% of the world’s
electricity in 2012, according to
the International Energy
Agency.
Nuclear power plants use nuclear fuel to create heat
which boils water, creating steam, which turns the turbine
to generate the electricity.
Radioactive dating is a process
used to determine the
approximate age of an object.
The amount of radioactive
nuclides present in the object,
such as a rock, can be
measured.
The half-life of the radioactive
nuclide must be known, and from
there, the age of the object can
be estimated.
Half-life: the
time it takes
for half of a
given amount
of radioactive
material to
decay.
Carbon-14 is a radioactive
nuclide often used to
estimate the age of
organic material
Approximate amounts of
radiation can be detected by
the following devices:
•Film badge
•Geiger-Muller counter
•Scintillation counter
The film badge is worn on a
lapel, the wrist, or finger,
and detects the approximate
accumulated dose of
radiation over time.
People who work with radiation, such
as x-ray technicians, will wear such a
device.
The Geiger-Muller counter detects
the approximate radiation present
at any given time by counting
electric pulses carried by gas
ionized by radiation.
The Geiger-Muller counter would be
used to detect an approximate
radiation dose that a person has
been exposed to, such as when the
Fukushima nuclear power plant
leaked radiation.
The scintillation counter can
detect ionizing radiation. Some
substances absorb ionizing
radiation and emit visible light, or
scintillate.
A scintillation counter would be used
in border security, homeland
security, and nuclear plant safety,
among other things.
For More Information…
Information about radiation
exposure - Hiroshima, Chernobyl,
Three Mile Island
Information on Effects of Nuclear
Weapons
Information on: What is
Radioactivity? What is Radiation?