chemistry chapter 3 and 24 atoms, ions, isotopes and nuclear chemistry these notes will enable the...

Chemistry Chapter 3 and 24

Atoms, Ions, Isotopes and Nuclear Chemistry

These notes will enable the student to understand concepts

related to the nucleus of the atom and basic nuclear chemistry

Chapter 24 Nuclear ChemistrySection 1: Radioisotopes

A. General Information 1. Carbon atoms can be stable or unstable 2. Many other atoms have the same

characteristics of stability These combination of unstable and stable forms of the

same atom are called Isotopes

I. Radioisotopes

B. Radioisotope 1. All nuclear decay is accompanied by radiation

emission a. called radioactivity b. discovered in 1896 by H. Becquerel by placing

photo film in a drawer with uranium ore c. film showed signs of exposure d. radiation passed through a piece of black paper

and produced an image on the film

I. Radioisotopes

B. Radioisotope 2. Decay of unstable isotopes is spontaneous

a. all elements have 1 or more isotopes b. the unstable isotopes decay to produce other

elements c. many elements have at least 1 radioactive isotope

or radioisotope that occurs naturally Fluorine is an example of one that does not have 1

radioisotope (F-19 is stable)

I. Radioisotopes

C. Half-life 1. Definition: The half-life of a radioactive isotope

is the same time it takes for ½ of a sample of isotope to decay a. follow an example: Rb – 2 isotopes, 85Rb and 87Rb

85Rb is 72.15% of total amount (in nature)

87Rb is 27.85% of total amount (in nature)

85Rb is stable

87Rb is radioactive (gives off Beta decay particles)

I. Radioisotopes

C. Half-life (cont) 1. Definition (cont)

87Rb 87Sr + 0e

37 38 -1

Remember, with Beta decay, a neutron is converted to 1 proton and 1 electron. So they lose the electron, but the proton remains (+1 proton = new element). In some cases, the electron stays and the proton is released

I. Radioisotopes


b. second example: Tin-124 (124Sn) 124Sn 124Sb + 0e 50 51 -1

c. The half-life of 87Rb is 6x1010 years (60 billion)In 60 Billion years ½ of the concentration of 87Rb in the sample would be converted to 87SrSo, if we start with 1.000g, in 60 billion years we would have ______g. In another 60 billion years we would have _____g.

I. Radioisotopes


d. the slower the decay, the slower the radioactive production

2. Examples of Radioactive isotopesForms Isotopes Half-life (yrs) Decay Type

Uranium-238 4.5x109 alphaNatural Uranium-235 7.1x108 alpha

Thorium-232 1.4x1010 alphaPotassium-40 1.3x109 betaCarbon-14 5730 alpha

I. Radioisotopes

C. Half-life (cont) 2. Examples of Radioactive isotopesForms Isotopes Half-life (yrs) Decay Type

Plutonium-239 24,000 alpha

Unnatural Cesium-137 30 beta

Strontium-90 28.8 beta

Iodine-131 .022 beta

I. Radioisotopes

D. Nuclear Bombardment Reactions 1. General Information

a. Radioactive isotopes go through spontaneous nuclear reactions to become stable

b. It is possible to make a stable isotope unstable Nuclear Bombardment

I. Radioisotopes


a. A nuclear bombardment reaction is when an atom is bombarded with a stream of particles (ex. Alpha)

When particles hit, they combine to become a new nucleus Discovered by Ernest Rutherford Discovered when an alpha particle strikes a 14Nitrogen

nucleus, an Oxygen-12 and Hydrogen-1 are produced.

24O + 7

14N 817O + 1

1H

Mass numbers and atomic numbers are balanced

I. Radioisotopes


b. Using alpha particles are difficult because both nuclei have (+) positive charges. Alpha particles must move extremely fast. Sometimes called atom smashers (particle accelerators) Several types of particle accelerators

I. Radioactive Isotopes


c. Using neutrons (particles) can create artificial radioactive isotopes. example.: Molybdenum -98 to technecium-99

01n + 42

98Mo 4399TC + -1

0e

Technecium-99 is used to detect brain tumors Neutron particles produces an electron (1

0e), it is not a B particle because a neutron is not changed into one proton and one electron.

Radioactive Isotopes


Sample problem “The neutron bombardment of calcium-40 produces

potassium-40 and “possibly” another particle as a byproduct.” Write the nuclear equation for this reaction. If it is potassium-40 and a secondary particle, the particle

chemistry chapter 3 and 24 atoms, ions, isotopes and nuclear chemistry these notes will enable the...

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