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# Isotopes PowerPoint PPT Presentation

Isotopes. Isotopes. Remembering back to Dalton's atomic theory: He stated that all atoms of the same element are identical. That is not true. The nuclei of atoms must contain the same number of protons in order to maintain the elements characteristics. Isotopes.

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Isotopes

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### Isotopes

• Remembering back to Dalton's atomic theory:

• He stated that all atoms of the same element are identical.

• That is not true.

• The nuclei of atoms must contain the same number of protons in order to maintain the elements characteristics.

### Isotopes

• However, the number of neutrons may vary.

• Atoms that have the same number of protons but different numbers of neutrons are called isotopes.

### Atomic Mass

• The atomic mass of an element is the weighted average of the masses of the isotopes of that element.

• The atomic mass reflects both the mass and relative abundance of the isotopes as they are found in nature.

### Atomic Mass

• Example: Carbon has 2 naturally occurring isotopes. Carbon-12 and 13. Ina sample of carbon 98.89% of the carbon is Carbon-12 and 1.11% is Carbon-13. To calculate the average atomic mass of carbon both isotopes must be taken into account.

• Average=(Atomic Mass A)(% of A)+ (Atomic Mass of B)(% of B)

• =(12u)(.9889)+ (13u)(0.0111)

• =11.87u+.144u

• =12.01u

### Applications of Isotopes

• Carbon dating

• Carbon-14 is created by the bombardment of the atmosphere by cosmic rays.It is an unstable radioactive isotope of C=12. After creation it finds its way into living organisms. When an organism dies no more C-14 is added and what C-14 is present continues to decay. To date artifacts scientists compare the number of C-14 atoms to the more common C-12 atoms in the artifact. This ratio along with the half-life of radioactive C-14 allows dating to occur.

### Applications of Isotopes

• Structural determination of compounds

• Isotopes are used to trace the formation of structures by acting as labels.

• Medical Uses

• Isotopes are used for diagnosis in medicine.

• Sodium-24 used to trace blood flow in the body so that obstructions can be detected.

• Iodine-131 has been used to test the activity of the thyroid gland

### Chemistry in the Environment

• The processing of uranium ore for nuclear fuel produces large amounts of radioactive mill tailings. Until the late 1970’s disposal of the radioactive tailings was not controlled. As a result , millions of tons of these radioactive tailings are present in unmarked sites across the United States and Canada.