ISOTOPES.

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Presentation transcript:

ISOTOPES

Atom Review All matter is made up of elements (e.g. carbon, hydrogen, etc.). The smallest part of an element is called an atom. Atom of different elements contain different numbers of protons. The mass of an atom is almost entirely due to the number of protons and neutrons.

The Atom The atom consists of two parts: 1. The nucleus which contains: protons neutrons 2. Orbiting electrons.

X A Z Isotopic Notation Mass number = number of protons + number of neutrons A X Element symbol Z Atomic number = number of protons Isotopic Notation

X A Z A = number of protons + number of neutrons (mass number) Z = number of protons (atomic number) A – Z = number of neutrons Number of neutrons = Mass Number – Atomic Number

ISOTOPES THE NUMBER OF PROTONS FOR A GIVEN TYPE OF ATOM NEVER CHANGES. THE NUMBER OF NEUTRONS CAN CHANGE. TWO ATOMS WITH THE SAME NUMBER OF PROTONS BUT DIFFERENT NUMBERS OF NEUTRONS ARE CALLED ISOTOPES.

ISOTOPES ISOTOPES ARE ATOMS WITH THE SAME NUMBER OF PROTONS BUT DIFFERENT NUMBER OF NEUTRONS.

U U 235 92 238 92 EXAMPLES OF URANIUM ISOTOPES: A Z Number of protons Number of neutrons A Z Number of protons Number of neutrons

U U 235 92 238 92 EXAMPLES OF URANIUM ISOTOPES: A 235 Z 92 Number of protons Number of neutrons 143 A 238 Z 92 Number of protons Number of neutrons 146 Isotopes of any particular element contain the same number of protons, but different numbers of neutrons.

So what are isotopes good for? Dope testing - one of the initial tests to determine if someone has been doping with synthetic testosterone is a test for a high concentration of an isotope that’s not contained within naturally produced testosterone, but within the synthetic testosterone derived from yams. More tests will have to be conducted if it is revealed that the athlete is a vegetarian with an affinity for yams.

Radiometric Dating

Making Bombs

Atomic Weight To calculate the atomic weight (average atomic mass) for a particular element we must consider how much of one isotope of an element exists versus another isotope of the same element. These are the "natural" abundances (% abundance) on earth.

Rule for Calculating Atomic Weight To calculate the average atomic weight, each exact atomic weight is multiplied by its percent abundance (expressed as a decimal). Then, add the results together and round off to an appropriate number of significant figures.

This is the solution for nitrogen: Example #1: Nitrogen mass number exact weight percent abundance 14 14.003074 99.63 15 15.000108 0.37 This is the solution for nitrogen: (14.003074) (0.9963) + (15.000108) (0.0037) = 14.007

Practice Problem # 1 Calculate the average atomic weight for magnesium: mass number exact weight percent abundance 24 23.985042 78.99 25 24.985837 10.00 26 25.982593 11.01

This is the solution for magnesium: Answer # 1 This is the solution for magnesium: (23.985042) (0.7899 ) + (24.985837) (0.1000) + (25.982593) (0.1101)= 24.305