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. Atoms 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.

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.

Example #1: Nitrogen This is the solution for nitrogen: mass number percent abundance in decimal form 14 15 percent abundance 99.63% 0.9963 0.37% 0.0037 This is the solution for nitrogen: (14) (0.9963) + (15) (0.0037) =

percent abundance in decimal form Practice Problem # 1 Calculate the average atomic weight for magnesium: mass number percent abundance in decimal form 24 25 26 percent abundance 78.99% 0.7899 10.00% 0.1000 11.01% 0.1101

This is the solution for magnesium: Answer # 1 This is the solution for magnesium: (24) (0.7899 ) + (25) (0.1000) + (26) (0.1101) =