Calculate Atomic Mass From Isotopes

Atomic Mass Formula:

\[ \text{Atomic Mass} = \frac{\sum (\text{Abundance} \times \text{Isotope Mass})}{100} \]

Calculated Atomic Mass:

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1. What is Atomic Mass?

Atomic mass is the weighted average mass of all naturally occurring isotopes of an element, taking into account their relative abundances. It's measured in atomic mass units (amu), where 1 amu is defined as 1/12th the mass of a carbon-12 atom.

2. How to Calculate Atomic Mass from Isotopes

The formula for calculating atomic mass from isotopes is:

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

Where:

Isotope Mass — Mass of each isotope in atomic mass units (amu)
Abundance — Natural abundance of each isotope (percentage)

Example: For an element with two isotopes:

Isotope A: 50 amu (30% abundance)
Isotope B: 52 amu (70% abundance)

Atomic Mass = (50×30 + 52×70)/100 = 51.4 amu

3. Why Calculate Atomic Mass?

Details: Knowing the atomic mass is essential for chemical calculations, including stoichiometry, molar mass determinations, and understanding periodic trends. It helps predict how elements will behave in chemical reactions.

4. Using the Calculator

Tips:

Enter the mass of each isotope in atomic mass units (amu)
Enter the natural abundance of each isotope as a percentage
You can add multiple isotopes using the "Add Another Isotope" button
The calculator automatically weights each isotope by its abundance

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between atomic mass and mass number?
A: Mass number is the sum of protons and neutrons in a specific isotope, while atomic mass is the weighted average of all naturally occurring isotopes.

Q2: Why are atomic masses on the periodic table not whole numbers?
A: They're weighted averages of all naturally occurring isotopes, which typically have different masses and abundances.

Q3: How precise should my isotope masses be?
A: For most calculations, 4 decimal places (e.g., 15.9949 for oxygen-16) provides sufficient precision.

Q4: What if my abundances don't add up to 100%?
A: The calculator normalizes the abundances, so you can enter either percentages (total 100%) or relative abundances.

Q5: Can I use this for radioactive elements?
A: This calculator is designed for stable isotopes. For radioactive elements, half-life must also be considered.