1. What is Atomic Mass?

Atomic mass is the weighted average mass of all naturally occurring isotopes of an element, measured in atomic mass units (amu). It accounts for both the mass and relative abundance of each isotope.

2. How to Calculate Atomic Mass

The atomic mass is calculated using the formula:

Where:

• Isotope Mass — Mass of a specific isotope in atomic mass units (amu)
• Fractional Abundance — Natural abundance of the isotope as a decimal (sum of all abundances should equal 1)

Example Calculation: For an element with two isotopes:

• Isotope 1: 10.0129 amu (19.99% abundance)
• Isotope 2: 11.0093 amu (80.01% abundance)

Atomic Mass = (10.0129 × 0.1999) + (11.0093 × 0.8001) = 10.81 amu

3. Importance of Atomic Mass

Details: Atomic mass is crucial for chemical calculations including stoichiometry, molar mass determinations, and understanding periodic trends. It appears on the periodic table as the weighted average of all naturally occurring isotopes.

4. Using the Calculator

Instructions:

1. Enter the mass of each isotope in atomic mass units (amu)
2. Enter the fractional abundance of each isotope (as a decimal between 0 and 1)
3. Click "Add Another Isotope" if you need to calculate for more than two isotopes
4. Click "Calculate" to compute the atomic mass

Note: The sum of all fractional abundances should equal 1 (100%).

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 (always a whole number), while atomic mass is the weighted average of all naturally occurring isotopes (usually a decimal).

Q2: Why is atomic mass not a whole number?
A: Atomic mass is a weighted average that accounts for different isotopes with different masses and their natural abundances.

Q3: How precise should my isotope mass values be?
A: For accurate calculations, use isotope masses with at least 4 decimal places as found in standard reference tables.

Q4: What if my abundances don't add up to exactly 1?
A: The calculator will still work, but for accurate results, abundances should be normalized to sum to 1 (100%).

Q5: Where can I find isotope mass and abundance data?
A: The IUPAC publishes authoritative data on isotope masses and abundances in their periodic table and technical reports.