# Problem: A certain element X has four isotopes. 0.5600% of X has a mass of 83.91343 amu. 9.860% of X has a mass of 85.90927 amu. 7.000% of X has a mass of 86.90890 amu. 82.58% of X has a mass of 87.90562 amu.What is the average atomic mass of element X? Express your answer numerically to four significant figures.Atomic mass Since the number of neutrons varies in the periodic table, neither then number of neutrons nor the mass number (number of neutrons plus protons) is shown. What we do see is the atomic mass, or a weighted average of all the isotope masses. This is the noninteger listed with an element; it is the number with several decimal places. An element's atomic mass is the weighted average of the isotope masses. In other words, it is an average that takes into account the percentage of each isotope. To find the weighted average, multiply each isotopic mass by its relative abundance and find the sum for each isotope of an element.

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A certain element X has four isotopes.

• 0.5600% of X has a mass of 83.91343 amu.
• 9.860% of X has a mass of 85.90927 amu.
• 7.000% of X has a mass of 86.90890 amu.
• 82.58% of X has a mass of 87.90562 amu.

What is the average atomic mass of element X?

Atomic mass

Since the number of neutrons varies in the periodic table, neither then number of neutrons nor the mass number (number of neutrons plus protons) is shown. What we do see is the atomic mass, or a weighted average of all the isotope masses. This is the noninteger listed with an element; it is the number with several decimal places. An element's atomic mass is the weighted average of the isotope masses. In other words, it is an average that takes into account the percentage of each isotope. To find the weighted average, multiply each isotopic mass by its relative abundance and find the sum for each isotope of an element.