Phys141 Principles of Physical Science Chapter 10 Nuclear Physics

1. Phys141 Principles of Physical ScienceChapter 10 Nuclear Physics Instructor: Li Ma Office: NBC 126 Phone: (713) 313-7028 Email: malx@tsu.edu Webpage: http://itscience.tsu.edu/ma Department of Computer Science & Physics Texas Southern University, Houston Nov. 3, 2004

2. Topics To Be Discussed • Symbols of the Elements • The Atomic Nucleus • Skip §10.3 to §10.7

3. 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.

4. 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.

5. 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)

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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)

12. 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

13. 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

14. 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

15. Numbers for An Element (cont) • The general designation for a specific nucleus (for example, for element X): mass number X A chemical symbol Z N = A – Z atomic number

16. 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 properties 19 F 9

17. 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

18. 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

19. 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

20. 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