1 Chapters 18 NUCLEAR CHEMISTRY

2 CHAPTER OUTLINE  Atomic Structure Atomic Structure  Radioactivity Radioactivity  Alpha Decay Alpha Decay  Beta & Gamma Decays Beta & Gamma Decays  Radionuclide Radionuclide  Half Life Half Life  Nuclear Fission & Fusion Nuclear Fission & Fusion

3 ATOMIC STRUCTURE  The general designation for an atom is shown below: No. of protons No. of protons & neutrons

4 Example 1: Determine the number of protons, electrons and neutrons in a fluorine atom. # of protons = atomic no. (Z)= 9 # of electrons = # of protons = 9 # of neutrons = A-Z = 19-9 = 10

5 Example 2: Argon (Ar) has 18 protons, 18 electrons and 22 neutrons. Write a formula designation for an argon atom. Atomic no. = # of protons = 18 Mass no. = p + + n 0 = = 40

6 HISTORY OF RADIOACTIVITY  The discovery of radioactivity can be attributed to several scientists.  Wilhem Roentgen discovered X-rays in  Shortly after that, Henri Becquerel observed radioactive behavior while experimenting with salts of uranium.  However, the term radioactivity was first coined by Marie Curie in 1898.

7 RADIOACTIVITY  Radioactivity is the spontaneous emission of particles and/or rays from the nucleus of an atom.  Nuclides are said to be stable (non-radioactive) or unstable (radioactive).  All elements having an atomic number greater than 83 (bismuth) have unstable nuclei, which undergo spontaneous decay (disintegration), and are therefore radioactive.

8 RADIOACTIVITY  These elements can undergo one of 3 different kinds of decay called  (alpha),  (beta) and  (gamma).  When decaying, the original nucleus (A) changes into another nucleus (B) and gives off radiation (b). Parent Daughter Radiation

9 TYPES OF RADIATION  The three different kinds of radiations can be distinguished by their interactions with an electric field.   -Radiations carry a positive charge and are attracted to the negative plate.  β-Radiations carry a negative charge and are attracted to the positive plate.  γ-Radiations carry no charge and are attracted to neither plate.

10 TYPES OF RADIATION  The three different kinds of radiations have different energies and penetration abilities.  α-Particles have low energy and can be blocked by a thin sheet of paper.  β-Particles have moderate energy and can be blocked by a thin sheet of metal.  γ-Rays have high energy and can only be blocked by a thick sheet of lead.

11 ALPHA DECAY  Alpha decay occurs when a nucleus changes into another nucleus and gives off an  -particle, which is a helium nucleus  Note that the sum of the atomic numbers and the mass numbers on the left and the right side of the equation are equal. 90 = = Loss of alpha particle from the nucleus results in loss of 4 in mass number (A) and 2 in atomic number (Z).

12 Examples: 1. undergoes alpha decay. Write the equation for this process. 92 – 2 = – 4 =

13 Examples: 2. Write the equation for alpha decay of radium isotope 88 – 2 = – 4 =

14 BETA DECAY  Beta decay occurs when a nucleus changes into another nucleus and gives off a ß-particle, which is an electron  In beta decay, a neutron is transformed into a proton and an electron. The proton remains in the nucleus, while the electron is emitted as a beta particle. 6 = =

15 GAMMA DECAY  Gamma decay occurs when a nucleus gives off  -rays, and becomes a less energetic form of the same nucleus. More energetic Less energetic gamma radiation

16 Examples: 1. Complete the following equation for nuclear decay: γ-decay

17 Examples: 2. Complete the following equation for nuclear decay: β-decay 47 = =

18 POSITRON DECAY  Certain nuclear processes can also lead to a fourth form of radiation, called a positron 17 = = positron

19 REVIEW: TYPES OF RADIATION  Alpha () particle is two protons and two neutrons  Beta () particle is a high-energy electron  Positron ( + ) is a positive electron  Gamma ( ) ray is high-energy released from a nucleus General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

20 SUMMARY OF TYPES OF RADIATION General, Organic, and Biological Chemistry

21 RADIONUCLIDES  A nuclide will be radioactive if it meets any of the following criteria: 1. Its atomic number is greater than It has fewer n 0 than p + in the nucleus. 3. It has odd # of n 0 and odd # of p +.

22 Examples: Which is the radionuclide in each of the following pairs: Z > 83 n 0 < p + p + and n 0 are odd

23 SMOKE DETECTORS  A practical use of radionuclides is their use in some smoke detectors.  In these detectors, a radionuclide decays to form α–particles.  The α–particles ionize (charge) the air particles and keep a current running through the circuit.  When smoke particles interfere with the ions, current is reduced in the circuit, and a alarm goes off.

24 HALF-LIFE The half-life of a radioisotope is the time for the radiation level to decrease (decay) to one-half of the original value. General, Organic, and Biological Chemistry

25 DECAY CURVE A decay curve shows the decay of radioactive atoms and the remaining radioactive sample. General, Organic, and Biological Chemistry

26  Each half-life reduces the amount of radio- nuclide to half of the previous amount. DECAY CURVE

27 Example 1: Iodine-131 has a half-life of 8 days. What mass of a 40 g sample of iodine-131 will remain after 24 days. 40 g 1st ½ -life 20 g 2nd ½ -life 10 g 3rd ½ -life 5 g

28 Example 2: How long would it take for a sample of C-14 to decay from 20.0 g to g? (½- life of C=14 = 5730 y) ½ life g

29 NUCLEAR FISSION  Fission is the process by which a large nucleus is “split” into smaller nuclei, with a large amount of energy released.

30 NUCLEAR FISSION DIAGRAM AND EQUATION General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.  A nuclear bomb is an example of an uncontrolled fission, while a nuclear reactor is an example of a controlled fission.

31 CHAIN REACTION A chain reaction occurs  when a critical mass of uranium undergoes fission  releasing a large amount of heat and energy that produces an atomic explosion General, Organic, and Biological Chemistry

32 NUCLEAR POWER PLANTS In nuclear power plants,  fission is used to produce energy  control rods in the reactor absorb neutrons to slow and control the chain reactions of fission General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

33 NUCLEAR FUSION Nuclear fusion  occurs at extremely high temperatures ( °C)  smaller nuclei combine to form larger nuclei  large amounts of energy are released  this occurs continuously in the sun and stars General, Organic, and Biological Chemistry

34 NUCLEAR FUSION  The sun uses fusion to produce a helium nucleus from 4 hydrogen nuclei, giving off 2 positrons and energy.

35 THE END