Transcript Slide 1
Daily Science • Who discovered the electron and how did he discover it? What was his model called? • What tells you the number of p+ an element has? • Write Manganese in short hand notation. Element Symbol Atomic # Cr Protons Neutrons 28 33 Electrons Mass # Atomic Mass Atomic Mass and isotopes Pg. 31 Isotopes • An isotope is an element that has the same number of protons but a different number of neutrons. • Ex. Carbon has 2 common isotopes: – Carbon-12 Carbon-14 • The numbers represent the mass number Atomic Mass • Atomic mass units (amu) are used to express an atoms mass • Atomic mass units are based off the element Carbon (amu= 1/12 the mass of Carbon) Average atomic mass • Average atomic mass is a weighted average of the isotopes of a given element. • More common isotopes have a greater effect on the average atomic mass than do less common isotopes. • Ex. Chlorine- 37 and Chlorine- 35 (average atomic mass is 35.45) Percent Abundance • The atomic mass can be calculated by summing the products of each isotope’s percent abundance and that isotope’s atomic mass. • Mass contribution tells how much of each isotope contributes to the total atomic mass. • Mass contribution = (% abundance written as a decimal) x (atomic mass) Average atomic mass • Aam = [(% abundance)(atomic mass)]1 + [(% abundance)(atomic mass)]2 + ….. Percent Abundance example • Chlorine 35 has an atomic mass of 34.969 amu and its percent abundance 75.770%. What is its mass contribution? • Chlorine 37 has an atomic mass of 36.966 amu and its percent abundance is 24.230%. What is its mass contribution. • Using the two previous answers, what is the average atomic mass of Chlorine?