Lecture 22 Chapter 13 The Atom & Nuclear Power

Thoughts on Chapter 13 From what we have studied to date, we are indeed entering a new era of alternative energy. We cannot, however, forget the current energy choices and their ramifications on our environment, life style, and the future of our children. It is our hope that emotion can be put aside and the material examined in a rational manner so that you can make educated choices needed to develop an energy policy that serves us all.

Atomic Hypothesis Atoms (from Greek atomos, meaning indivisible) Named by Democritus in 420 BC, idea was ahead of its time Aristotle in 320 BC believed that all matter originated from the 4 elements, (air, fire, water, earth). This view was maintained for nearly 2000 years.

Atomic theory was revived by English chemist John Dalton about the turn of century He concluded that every element was made up of atoms By studying chemical reactions, he identified 20 different kinds of atoms Today we know that there are more than 100

Fig. 13-1a, p. 428 Fig. 13-1b, p. 428 Evacuated tube used to observe cathode rays. Apparatus used to measure charge- to-mass ratio of the electron

Radioactivity Henri Becquerel and Marie and Pierre Curie observed that several massive elements emitted radiation spontaneously Observed various types of radiation –Alpha (positive charged) –Beta (negative charged) –Gamma (similar to X-rays) Discovered that chemical transformation occurs after emission of radiation

Nucleus Geiger and Marsden observed that Alpha particles were deflected through very large angles Rutherford concluded that nucleus was core of an atom and very small Nucleus contains 99.9% weight of atom –Protons (positively charged particles) –Neutrons (neutral charged particles) Smallest particles are quarks 3 quarks combine to make one proton of +1 charge

Fig. 13-4, p. 431 Fermi, Batavia, ILSee also LHC:

Number of protons in Nucleus = Atomic Number Atoms in various configurations form molecules Bonds between elemental particles in the nucleus are related to nuclear energy and are electrical in nature Electrons have both kinetic and electrical energy

Fig. 13-6, p. 433

Fig. 13-5, p. 432 Carbon atom nucleus has a charge of +6. The number of protons gives the element its atomic number. Z: atomic # (# of protons) A: atomic weight (# protons + neutrons)

Atomic Spectrum Various elements when excited by heat or electrical discharge emit different colored light –Neon is red –Mercury is blue-purple –Sodium is yellow Colors caused by the transition of electrons from an excited state back to a unique lower energy level If viewed through a slit and prism, will yield distinct bands of color marking wavelengths. These wavelengths are used to determine the composition of elements of the source. (like a finger print)

Fig. 13-7, p. 434

Fig. 13-8a-c, p. 435 Isotopes of hydrogen - have same number of protons, but different numbers of neutrons and therefore different masses.

Table 13-1, p. 436  particles are nuclei of He atoms (2 protons & 2 neutrons)  particles are electrons or positrons  rays are electromagnetic waves

Transmutation As protons in the nucleus change, so do elements. If the new element is also radioactive, then it will digress into another element as decay continues. This process will eventually end when the final element is no longer radioactive and considered “stable”.

Fig. 13-9, p. 436 Radioactive  decay of 238 U Th: Thorium Pa: Protactinium

Fig , p. 437 Radioisotope Half-life Polonium seconds Bismuth seconds Sodium-2415 hours Iodine days Cobalt years Radium years Uranium billion years

Fig a, p. 449

Fig b, p. 449 U

Nuclear Glue Binding energy of a nucleus is the energy needed to disassemble the nucleus into its individual parts. The larger the binding force the more stable the nucleus When a nucleus is split, the energy required to hold the two new nuclei is less than that required to hold the original. The remaining glue is energy. One gram of Helium formed as a product of fusion of protons and neutrons would yield the energy equivalent of burning 23,000 kg of coal.