CHAPTER 21 NUCLEAR CHEMISTRY

I. Ordinary Chemical Reactions A. Bond breaking, bond forming, only outer electrons of the atoms are disturbed. B. Nuclei of the atoms are unaffected. II. Nuclear Reactions A. Deals with changes in atomic nuclei.

B. Importance 1. Nuclear reactors - radioactivity 2. Atomic bombs – nuclear fission (splitting nuclei. 3. Hydrogen bomb – nuclear fusion (joining nuclei) II. Review of the nucleus of the atom A. Composed of nucleons – protons and ___________.

B. Each kind of nucleus is called a nuclide, characterized by its number of ____________ and number of ______________. C. Two atoms whose nuclei have the same no. of protons but a different no. of neutrons are called _________. D. The no. of protons is given the symbol ____.

E. The no. of protons and no. of ____________ is called the ______________ with the symbol __. F. X is the symbol for the element. G. Some nuclides:

III. There are two types of nuclear reactions. A. Radioactive decay – The process in which a nucleus spontaneously disintegrates, giving off __________. B. Nuclear bombardment reactions – Those reactions in which a nucleus is struck by another nucleus or by a nuclear _________.

IV. Radioactivity A. Discovered by Becquerel (1896 B. Photographic plates developed bright spots when exposed to ____________________. C. Later shown to be separable by electric and magnetic fields into three types; _______, _________, and ________________________.

1. Alpha rays bend away from a positive plate indicating they are _______________. They are known to consist of helium-4 nuclei. 2. Beta rays bend in the opposite direction indicating they have a ______________. They consist of high speed ___________.

C. Gamma rays – a form of electromagnetic radiation – wavelength ~ m V. Nuclear equations A. def. – a symbolic representation of a nuclear reaction B. Only nuclei are represented – not necessary to indicate electron charges for any ions involved.

D. Reactant and product nuclei are represented in nuclear equations by their ______ ________. E. Other particles are given the following symbols:

F. To balance nuclear reactions: 1. Sum of the mass numbers of the reactants must = the sum of the mass numbers of the __________. (A’s) 2. Sum of the atomic numbers (protons) of the reactants must = the sum of the atomic numbers of the _____________. (Z’s)

An example: First radioactive element found by Marie Curie – naturally decaying Polonium Notice 84 = (Z’s) sum of atomic numbers are equal on both sides. 212 = (A’s) equal too.

How would you complete the following? How will you identify the symbol for the element? What is its atomic number? _____ What is its mass number? What is its nuclide symbol? _____

G. Types of radioactive decay – spontaneous change of unstable nuclide. 1. Alpha emission – emission of alpha particle (α) Parent nuclide Daughter nuclide

Fill in the blank: 2. Beta emission – β-decay emission of Fill in the blank:

3. Positron emission β + decay Try this one:

4. Electron capture (EC) – one of the electrons in an atom is captured by the nucleus of the atom Try this one:

5. Gamma ray emission – in many cases, radioactive decay results in a daughter nucleus that is in an excited state; the excited state is unstable and goes to a lower-energy state by releasing energ y in the form of gamma rays.

VI. Nuclear Stability A. The nucleus of an atom is stable if it does NOT change into another nuclide without adding outside energy. B. Look at each element, determine what nuclides of the elements are stable, plot stable nuclides on graph. No. of protons x axis No. of neutrons y-axis

Which one lies on the N=Z line?

C. Band of stability 1. Lighter stable nuclei Z < As Z increases ratio increases to ~1.5 ( possible reason, as Z increases, the repulsion of the protons increases, and more neutrons are neede to give attractive nuclear force.

3. No stable nuclides Z > 83, all are radioactive.