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Phys141 Principles of Physical Science
Chapter 10
Nuclear Physics
Instructor: Li Ma
Office: NBC 126
Phone: (713) 313-7028
Email: [email protected]
Department of Computer Science & Physics
Texas Southern University, Houston
Nov. 3, 2004
Topics To Be Discussed
Symbols of the Elements
 The Atomic Nucleus
 Skip §10.3 to §10.7
About Atomic Nucleus
The atomic nucleus and its properties have
important impact on our society:
– Advantage:
Archeological dating
Diagnosis & treatment diseases, esp. cancer
Generation of electricity by nuclear energy
Formation of new elements
Shinning of the Sun and other stars
Smoke detector
About Atomic Nucleus (cont)
The atomic nucleus and its properties have
important impact on our society (cont):
– Disadvantage:
Radiation damage
Nuclear bomb
Disposal of nuclear waste
Symbols of the Elements
A brief history of how the concept of element
arose and how elements are expressed in
– About 600 to 200 B.C., Greek philosophers
speculated the basic substance or substances that
make up matter
Aristotle: 4 “elements”: earth, air, fire & water – wrong
– Discovery and properties of the true elements are
discussed in Chemical Elements (Chapter 11)
Symbols of the Elements (cont)
How are these true elements symbolized?
– Berzelius (in the early 1800s) started to use
symbol notation for elements
First one or two letters of the Latin name for each
– Since Berzelius’ time, most elements have been
symbolized by the first one or two letters of the
English name:
C for carbon; O for oxygen; Ca for calcium
First letter is always in upper case, second in lower case
Symbols of the Elements (cont)
Periodic table:
– Show the positions, names, and symbols of the
114 elements presently known
Table 10.2 on page 228
The Atomic Nucleus
All matter is made of atoms
 An atom is composed of negatively charged
electrons that surround a nucleus
 The nucleus is the central core of an atom. It
consists of positively charged protons and
neutrons, which are electrically neutral
The Atomic Nucleus (cont)
An electron and a proton have the same
magnitude of electric charge, but opposite
 A proton and a neutron have almost the same
mass, and are about 2000 times more than
an electron
 Nuclear protons and neutrons are collectively
called nucleons
The Atomic Nucleus (cont)
Rutherford’s alpha-scattering experiment
– The diameter of a nucleus is about 10-14 m
– The diameter of an atom (i.e. the orbits of the
atom’s outer electrons) is about 10-10 m
Electron orbits determine the size of atoms
 The nucleus contributes 99.97% of the mass
The Atomic Nucleus (cont)
Charge is due to moving of electrons, so it
seems electron is a truly fundamental particle
of matter
 However, further investigation have revealed
that there still exist smaller particles called
 Theoretically, six types of quarks exist
(verified experimentally as well)
Numbers for An Element
An element is defined as a substance in
which all the atoms have the same number of
 The atomic number (Z) is the number of
protons in the nucleus of each atom of that
 The atomic number also represents the
number of electrons in a neutral atom
Numbers for An Element (cont)
Electrons may be gained or lost by an atom
=> ion of that same element
– A sodium atom (Na) becomes a sodium ion (Na+)
by losing an electron
The neutron number (N) is the number of
neutrons in the nucleus
 The mass number (A) is the number of
protons and neutrons in the nucleus, i.e. it’s
the total number of nucleons
Numbers for An Element (cont)
Atom of the same element can be different
because of different numbers of neutrons in
their nuclei
 Forms of atoms that have same number of
protons but differ in their numbers of neutrons
are known as the isotopes of that element
– The isotopes of the same element have same Z
but different N and different A
Numbers for An Element (cont)
The general designation for a specific
nucleus (for example, for element X):
mass number
atomic number
chemical symbol
N =A–Z
Numbers for An Element (cont)
Determine the composition of an atom:
– Use N = A – Z
– Ex. The neutron number (N) for the following
element is 10
The isotopes of an element have the same
chemical properties but different physical
The Strong Nuclear Force
Two fundamental forces of nature:
electromagnetic and gravitational
 The electromagnetic force between a proton
and an electron is about 1039 times greater
than the corresponding gravitational force
 The electromagnetic force is the only
important force on the electrons in an atom
The Strong Nuclear Force (cont)
In an atom, the protons and neutrons are
packed together in the nucleus and electrons
circulate around the nucleus in am empty
 Coulomb’s law: like charges repel, unlike
charges attract
 A strong force must exist in nucleus to hold
the nucleus together
The Strong Nuclear Force (cont)
The third fundamental force of nature strong
nuclear force (or just strong force or nuclear
force) acts on neutrons
 The strong nuclear force is a short range
force (distance less than 10-14 m)
 A weak nuclear force also exists
– A short range force
– Stronger than gravitational force, but very much
weaker than strong nuclear force
Homework Assignment
– Review Questions (page 255):
– Exercises (page 257):
– It’s due Monday, 11/15/04
Reading Assignment
– Chapter 15: §15.5 – §15.7