Average Atomic Mass Calculator

Average Atomic Mass Formula:

\[ \text{Average Atomic Mass} = \sum (\text{Isotope Mass} \times \text{Fractional Abundance}) \]

Isotope Mass:

amu

Fractional Abundance:

(0-1)

Average Atomic Mass:

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1. What is Average Atomic Mass?

The average atomic mass is the weighted average of the atomic masses of all naturally occurring isotopes of an element. It accounts for both the mass and relative abundance of each isotope.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \text{Average Atomic Mass} = \sum (\text{Isotope Mass} \times \text{Fractional Abundance}) \]

Where:

Isotope Mass — Mass of each isotope in atomic mass units (amu)
Fractional Abundance — Natural abundance of each isotope (0-1)

Explanation: The calculator multiplies each isotope's mass by its fractional abundance, sums all these products, and normalizes the result if the total abundance isn't exactly 1.

3. Importance of Average Atomic Mass

Details: The average atomic mass is what appears on the periodic table and is used in all chemical calculations involving mass. It's crucial for stoichiometry, analytical chemistry, and understanding elemental properties.

4. Using the Calculator

Tips:

Enter isotope masses in atomic mass units (amu)
Enter fractional abundances as decimals between 0 and 1
Click "Add Another Isotope" to include multiple isotopes
Abundances don't need to sum to exactly 1 - the calculator will normalize them

5. Frequently Asked Questions (FAQ)

Q1: Why isn't atomic mass a whole number?
A: Atomic masses are weighted averages of all naturally occurring isotopes, which have different masses due to varying numbers of neutrons.

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.

Q3: How precise should my inputs be?
A: For accurate results, use isotope masses and abundances with at least 4 decimal places, especially for elements with very rare isotopes.

Q4: What if my abundances don't sum to 1?
A: The calculator will normalize your inputs by dividing each abundance by the total, so they'll be treated as relative proportions.

Q5: Can I use percentage abundances instead of fractions?
A: Yes, just divide percentages by 100 before entering them (e.g., 25% → 0.25).