2. SCOPE OF STUDY
SCOPE OF STUDY
11 main sub topics students should learn and understand in this
chapter are :
Structure and Properties of the Nucleus
Discovery of Neutrons
The Nuclear Forces
Atomic Number and Mass Number
Atomic Mass Unit
3. SCOPE OF STUDY
SCOPE OF STUDY
Mass Defect
Binding Energy per Nucleon
Mass-Energy Equation
Isotopes of an Element
Mass Spectrometer
Detection of Presence of Isotopes
4. STRUCTURE &
STRUCTURE &
PROPERTIES OF
PROPERTIES OF
NUCLEUS
NUCLEUS
Nucleus consists of protons and neutrons.
A proton is the nucleus of the simplest atom hydrogen.
Proton has positive charge.
Neutron carries no electric charge and has mass slightly larger than a proton.
The number of neutrons in the nucleus is N.
7. STRUCTURE &
STRUCTURE &
PROPERTIES OF
PROPERTIES OF
NUCLEUS
NUCLEUS
Neutrons and protons are collectively called nucleons.
Although hydrogen nucleus consists of a single proton alone, the nuclei of all
other elements consist of both neutrons and protons.
Nuclei is a plural of nucleus.
The different nuclei are often referred to as nuclides.
The radius, r of nucleus depends on atomic mass number, A
(
r ≈ 1.2 ×10
−15
)
13
mA
9. DISCOVERY OF
DISCOVERY OF
NEUTRONS
NEUTRONS
In 1932, Chadwick proved the existence of neutrons - elementary particles
devoid of any electrical charge.
In contrast with the helium nuclei (alpha rays) which are charged, and therefore
repelled by the considerable electrical forces present in the nuclei of heavy atoms,
this new tool in atomic disintegration need not overcome any electric barrier and is
capable of penetrating and splitting the nuclei of even the heaviest elements.
11. DISCOVERY OF
DISCOVERY OF
NEUTRONS
NEUTRONS
Chadwick smashed alpha particles into beryllium, a rare metallic element,
and allowed the radiation that was released to hit another target: paraffin
wax. When the beryllium radiation hit hydrogen atoms in the wax, the atoms
were sent into a detecting chamber. In physics it is known that only a particle
having almost the same mass as a hydrogen atom could effect hydrogen in
that manner. The experiment results showed a collision with beryllium atoms
would release massive neutral particles, which Chadwick named neutrons.
12. NUCLEAR FORCES
NUCLEAR FORCES
Two types : Strong nuclear forces and weak nuclear forces.
Strong nuclear force is an attractive force that acts between all nucleons
(protons and neutrons alike).
Protons attract each other via strong nuclear force at the same time they repel
each other via electric force.
Strong nuclear force > electric force.
Neutrons (electrically neutral) only attract other neutron or protons via strong
nuclear force.
13. NUCLEAR FORCES
NUCLEAR FORCES
Strong nuclear force is a short-range force. It acts only over a very short
distance.
It is very strong between 2 nucleons if they are < 10 -15 m apart.
It is 0 if they are separated by a distance > 10 -15 m apart.
Electric and gravitational forces are long-range forces.
If the nuclide contains too fewer or too many neutrons relative to the number of
protons, the binding of nucleons reduce (nuclide unstable).
14. NUCLEAR FORCES
NUCLEAR FORCES
Nuclei stable – have the same number of protons as neutrons (N=Z) up to about
A = 30.
Beyond this, stable nuclei contain more neutrons and protons.
As Z increase, electric repulsion increase, greater number of neutrons require to
maintain stability.
For very large Z, no number of neutrons can overcome the greatly increased
electric repulsion. (Above Z = 82, no completely stable nuclide).
Weak nuclear force – second type of nuclear force that is much weaker than
strong nuclear force.
16. ATOMIC NUMBER, Z
ATOMIC NUMBER, Z
DEFINITION
DEFINITION
Number of protons in the nucleus
To establish the chemical identity of the atom.
Each atomic number corresponds to a different chemical element.
It symbols by Z.
17. MASS NUMBER, A
MASS NUMBER, A
DEFINITION
DEFINITION
Total number of protons and neutrons
(nucleons) in the nucleus
Neutron number : N = A - Z
18. MASS NUMBER, A
MASS NUMBER, A
It symbols by A.
A and Z sufficient to specify a nuclide.
Nuclide are symbolized by symbol :
X is the chemical symbol for the element.
It contains the same information of
recognizable form.
Z
but in the more easily in the
19. ATOMIC MASS UNIT
ATOMIC MASS UNIT
It is symbolized by amu or u.
It is a unit to specify the nuclear masses because the very small size of protons it
is not convenient to express the mass of nuclei and atomic particles in the
conventional unit of kilograms.
Masses of atoms are measured with reference to the carbon-12 atom, which is
assigned a mass of exactly 12 u.
20. ATOMIC MASS UNIT
ATOMIC MASS UNIT
The relationship between the atomic mass unit and kilogram is :
where c : speed of light = 3.0 x 108 m/s
22. MASS DEFECT, ∆m
MASS DEFECT, ∆m
DEFINITION
DEFINITION
The amount by which the sum of the individual masses
The amount by which the sum of the individual masses
of the protons and neutrons exceeds the mass of intact
of the protons and neutrons exceeds the mass of intact
nucleus
nucleus
It is also known as the difference in mass of the nucleus.
23. BINDING ENERGY PER
BINDING ENERGY PER
NUCLEON
NUCLEON
BINDING ENERGY
The energy needed to break the nucleus into its
The energy needed to break the nucleus into its
constituent protons and neutrons ((nucleons).
constituent protons and neutrons nucleons).
24. BINDING ENERGY PER
BINDING ENERGY PER
NUCLEON
NUCLEON
Because of the strong nuclear force, the nucleons in a stable nucleus are held
tightly together.
Thus, energy is required to separate a stable nucleus into its constituent
nucleons.
The more stable the nucleus is, the greater is the amount of energy needed to
break it apart.
Each of the separated nucleons is at rest and out of range of the forces of the
other nucleons.
26. BINDING ENERGY PER
BINDING ENERGY PER
NUCLEON
NUCLEON
BINDING ENERGY PER NUCLEON
The total binding energy of a nucleus divided by
The total binding energy of a nucleus divided by
mass number, A
mass number, A
28. BINDING ENERGY PER
BINDING ENERGY PER
NUCLEON
NUCLEON
Example: Binding energy for iron.
Calculate the total binding energy and the binding energy per nucleon for
,
the most common stable isotope of iron.
Solution:
Calculate the mass of the iron nucleus, the mass of 26 protons, and the
mass of 30 neutrons. The total binding energy is the difference, 492
MeV, and the binding energy per nucleon is 8.79 MeV.
29. MASS-ENERGY
MASS-ENERGY
EQUATION
EQUATION
The energy change in a nuclear reaction is considerably greater than that of a
normal chemical reaction.
This change can be calculated using Einstein's equation:
ΔE = Δmc22
ΔE = Δmc
where ΔE is the change in energy,
Δm is the change in mass,
c is the speed of light (3.00 x 108 m/s).
32. ISOTOPES OF
ISOTOPES OF
ELEMENT
ELEMENT
Every nuclide is an isotope of some other nuclide.
Most elements have several isotopes.
In most cases some of the isotopes of a given element are stable (not
radioactive), and some are radioactive.
For example, iodine has 23 known isotopes with mass numbers ranging from
117 to 139.
Two of these, I-127 and I-131, are shown below.
34. ISOTOPES OF
ISOTOPES OF
ELEMENT
ELEMENT
The relationship between the two nuclides is that they are isotopes.
I-131 is an isotope of I-127, and I-127 is also an isotope of I-131.
For most elements the most common or most abundant form is the stable
isotope.
The radioactive forms are therefore isotopes of the more common forms,
explaining the strong association isotopes have developed with radioactivity.
36. MASS
MASS
SPECTROMETER
SPECTROMETER
DEFINITION
DEFINITION
An instrument which can measure the masses and
An instrument which can measure the masses and
relative concentrations of atoms and molecules. It
relative concentrations of atoms and molecules. It
makes use of the basic magnetic force on a moving
makes use of the basic magnetic force on a moving
charged particle.
charged particle.
38. DETECTION OF
DETECTION OF
PRESENCE OF
PRESENCE OF
EXAMPLE
ISOTOPES
ISOTOPES
Two radioactive isotopes of sodium—sodium-22 and sodium-24—are used
Two radioactive isotopes of sodium—sodium-22 and sodium-24—are used
in medicine and other applications. They can be used as tracers to follow
in medicine and other applications. They can be used as tracers to follow
sodium in aaperson's body. A tracer is aaradioactive isotope whose presence
sodium in person's body. A tracer is radioactive isotope whose presence
in aasystem can easily be detected. The isotope is injected into the system at
in system can easily be detected. The isotope is injected into the system at
some point. Inside the system, the isotope gives off radiation. That radiation
some point. Inside the system, the isotope gives off radiation. That radiation
can be followed by means of detectors placed around the system.
can be followed by means of detectors placed around the system.
39. DETECTION OF
DETECTION OF
PRESENCE OF
PRESENCE OF
ISOTOPES
ISOTOPES
Sodium-24 also has non-medical applications. For example, it is used to test
Sodium-24 also has non-medical applications. For example, it is used to test
for leaks in oil pipe lines. These pipe lines are usually buried underground.
for leaks in oil pipe lines. These pipe lines are usually buried underground.
It may be difficult to tell when aa pipe begins to leak. One way to locate aa
It may be difficult to tell when pipe begins to leak. One way to locate
leak is to add some sodium-24 to the oil. If oil leaks out of the pipe, so does
leak is to add some sodium-24 to the oil. If oil leaks out of the pipe, so does
the sodium-24. The leaking oil may not be visible, but the leaking sodiumthe sodium-24. The leaking oil may not be visible, but the leaking sodium24 is easily detected. It is located by instruments that are designed to detect
24 is easily detected. It is located by instruments that are designed to detect
radiation.
radiation.
40. ~~ THE END ~~
“ Write it on ur heart that every
day is the best day in the year”
~Ralph Wardo
Emerson~
