ISOTOPES AVERAGE ATOMIC MASS

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Presentation transcript:

ISOTOPES AVERAGE ATOMIC MASS

ISOTOPES Atoms of the same element with different mass numbers Atoms with the same number of protons, but different numbers of neutrons. ISOTOPES OF CHLORINE 35Cl 37Cl 17 17 Chlorine - 35 Chlorine - 37

FACTS ABOUT ISOTOPES Almost each element is found in the Universe as a mixture of isotopes Every isotope is found in nature in a fixed percentage called Isotopic Abundance Example: Magnesium can be found as a mixture of three isotopes 79% Magnesium-24, 10% Magnesium-25 and 11% Magnesium-26

FACTS ABOUT ISOTOPES These percentages are different for each element Each element has a particular number of isotopes The isotope notation includes the name or symbol of the element followed by the atomic mass. Example: Magnesium-25 or Mg-25

FACTS ABOUT ISOTOPES The existence of isotopes explains the fact that atomic mass is a decimal for most elements Isotopes of one element have the same chemical behaviour but slightly different physical properties Example: boiling point or melting point

FACTS ABOUT ISOTOPES They have lots of real life applications e.g. medical There are almost 2000 isotopes found The isotopes of radioactive elements are called Radioisotopes

LEARNING CHECK Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C 13C 14C 6 6 6 #p _______ _______ _______ #n _______ _______ _______ #e _______ _______ _______

AVERAGE ATOMIC MASS Where: Aav = average atomic mass Atomic mass is the weighted AVERAGE ATOMIC of all the atomic masses of the isotopes of that atom correlated with their isotopic abundances. Where: Aav = average atomic mass (%) = isotopic abundance

PRACTICE ONE Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine. Calculate the average atomic mass for Chlorine.

PRACTICE TWO Assume that the element 108Uno is synthesized and that the sample contains 25.2% 272Uno (271.4 amu), 30.8% 273Uno (272.3 amu) and 44.0% 275Uno (274.2 amu). Calculate the average atomic mass of Uno.

CALCULATING ISOTOPIC ABUNDANCE Steps: Assign variables for the isotopic abundances; x and y Write the equation for isotopic abundances: x + y = 1 Write the equation for the Average atomic mass: AAV = A1X1 + A2X2 Set both equation as a linear system and solve for x and y by substitution

PRACTICE THREE Boron exists as two naturally occurring isotopes: B-10.01a.m u and B-11.01a.m.u. Calculate the isotopic abundance of each isotope of Boron.

PRACTICE FOUR Silver (Atomic weight 107.868) has two naturally-occurring isotopes with isotopic weights of 106.90509 and 108.90470. What is the percentage abundance of each isotope in Silver?