Daily Sciencepg. 32

• 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?• What is an isotope?• Write Manganese-56 in short hand notation. How many no

does it have? Complete the following table.Element Symbol

Atomic # Protons Neutrons Electrons Mass # Atomic Mass

Cr 28

33

53 75

Ag 108

27 58.933

Atomic Mass

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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)• Found under the element symbol (usually)

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)

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?