Understanding Average Atomic Mass

What is the mass number of an element?

• The average atomic mass of an element

• The number of protons in an atom

• The number of neutrons in an atom

• The sum of protons and neutrons in an atom

Why is the average atomic mass of an element often a decimal?

• Because it includes the mass of electrons

• Because it is an average of isotopes with different masses

• Because it only considers the most abundant isotope

• Because it is rounded to the nearest whole number

What is an isotope?

• An element with a different number of protons

• An element with a different number of electrons

• An element with the same number of neutrons but different masses

• An element with the same number of protons but different masses

What does percent abundance indicate?

• The percentage of neutrons in an isotope

• The percentage of each isotope in a sample

• The percentage of an element in a compound

• The percentage of protons in an isotope

What is the first step in calculating the average atomic mass?

• Divide the total mass by the number of isotopes

• Add the masses of all isotopes

• Multiply the mass of each isotope by its percent abundance

• Convert percent abundance to a decimal

In the calculation of average atomic mass, what is done after converting percent abundance to a decimal?

• Add the decimal values together

• Multiply the mass of each isotope by the decimal

• Subtract the smallest mass from the largest

• Divide the total mass by the number of isotopes

What is the average atomic mass of potassium based on the example calculation?

• 38.0000 amu

• 39.1344 amu

• 40.0000 amu

• 41.0000 amu

Why might the calculated average atomic mass differ slightly from the periodic table?

• Due to different isotopes being used

• Due to incorrect percent abundances

• Due to rounding differences

• Due to incorrect mass numbers

What are the naturally occurring isotopes of gallium?

• Gallium-68 and Gallium-70

• Gallium-69 and Gallium-71

• Gallium-70 and Gallium-72

• Gallium-67 and Gallium-69

What is the calculated average atomic mass of gallium in the example?

• 71.0000 amu

• 70.0000 amu

• 69.7978 amu

• 68.0000 amu