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Transcript
Phys141 Principles of Physical Science
Chapter 10
Nuclear Physics
Instructor: Li Ma
Office: NBC 126
Phone: (713) 313-7028
Email: [email protected]
Webpage: http://itscience.tsu.edu/ma
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
Etc.
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
Etc.
Symbols of the Elements

A brief history of how the concept of element
arose and how elements are expressed in
symbols
– 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
element
– 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
signed
 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
showed
– 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
quarks
 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
protons
 The atomic number (Z) is the number of
protons in the nucleus of each atom of that
element
 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
A
Z
atomic number
X
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
19
9

F
The isotopes of an element have the same
chemical properties but different physical
properties
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
space
 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
Assignment

Homework Assignment
– Review Questions (page 255):

1,2,5,6,7,15
– Exercises (page 257):

2
– It’s due Monday, 11/15/04

Reading Assignment
– Chapter 15: §15.5 – §15.7