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Average Atomic Mass Formula:
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The average atomic mass is the weighted average of the atomic masses of all naturally occurring isotopes of an element. It takes into account both the mass and relative abundance of each isotope.
The calculator uses the formula:
Where:
Explanation: The calculator sums the product of each isotope's mass multiplied by its relative abundance to determine the weighted average atomic mass.
Details: Average atomic mass is fundamental to chemistry calculations, including stoichiometry, molar mass determinations, and understanding elemental properties. It appears on the periodic table as the standard atomic weight for each element.
Tips: Enter the mass of each isotope in amu and its fractional abundance (e.g., 0.25 for 25%). Click "Add Another Isotope" to include additional isotopes. All abundance values should sum to approximately 1 (100%).
Q1: Why is atomic mass not a whole number?
A: Atomic mass is a weighted average of all naturally occurring isotopes, which have different masses and abundances, resulting in a decimal value.
Q2: What's the difference between mass number and atomic mass?
A: Mass number is the sum of protons and neutrons in a specific isotope (always a whole number), while atomic mass is the weighted average of all isotopes (typically a decimal).
Q3: How accurate are periodic table atomic masses?
A: Very accurate. They represent carefully measured weighted averages of all naturally occurring isotopes based on their terrestrial abundances.
Q4: Can abundances be entered as percentages?
A: This calculator requires fractional values (e.g., 0.25 instead of 25%). Divide percentage values by 100 to convert them to fractions.
Q5: Why do some elements have atomic mass values in brackets?
A: Brackets indicate the atomic mass of the most stable or most common isotope, typically for synthetic elements without a standard atomic weight.