Multiple Choice
Which property of an element is determined by adding the number of protons and the number of neutrons?
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2. Atoms & Elements
Atomic Mass
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What is the average atomic mass of gallium (Ga) as listed on the periodic table?
A
69.72 u
B
63.55 u
C
72.64 u
D
65.39 u
Verified step by step guidance1
Understand that the average atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes, based on their relative abundances.
Identify the isotopes of gallium (Ga) and their respective atomic masses and natural abundances. For gallium, the two main isotopes are Ga-69 and Ga-71.
Use the formula for average atomic mass: \(\text{Average Atomic Mass} = (\text{fractional abundance of isotope 1} \times \text{mass of isotope 1}) + (\text{fractional abundance of isotope 2} \times \text{mass of isotope 2}) + \ldots\)
Plug in the values for gallium's isotopes: for example, if Ga-69 has an abundance of about 60.1% and Ga-71 about 39.9%, convert these percentages to decimals (0.601 and 0.399) and multiply by their respective masses (approximately 68.9257 u for Ga-69 and 70.9247 u for Ga-71).
Add the results from the previous step to find the weighted average atomic mass, which corresponds to the value listed on the periodic table.
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