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 each isotope in atomic mass units (amu)
• Relative Abundance — Natural abundance of each isotope as a percentage

Example: For an element with two isotopes (mass 10 amu at 20% and mass 11 amu at 80%), the atomic mass would be (10×0.20) + (11×0.80) = 10.8 amu.

3. Importance of Atomic Mass

Details: Atomic mass is fundamental in chemistry for stoichiometric calculations, determining molar masses, and understanding periodic trends. It's crucial for accurate chemical measurements and reactions.

4. Using the Calculator

Tips:

1. Enter the number of isotopes (usually 2-5 for most elements)
2. For each isotope, enter its exact mass and natural abundance percentage
3. Ensure the abundance percentages sum to exactly 100%
4. Click calculate to get the weighted average atomic mass

5. Frequently Asked Questions (FAQ)

Q1: Why is atomic mass not a whole number?
A: Atomic mass is a weighted average of all naturally occurring isotopes, which typically have different masses and abundances.

Q2: How precise should isotope masses be?
A: For accurate results, use isotope masses to at least 4 decimal places from reliable reference tables.

Q3: What if abundances don't sum to 100%?
A: The calculator will show an error. Natural isotope abundances always sum to 100% for any element.

Q4: How does this differ from mass number?
A: Mass number is the sum of protons and neutrons in a single isotope (always a whole number), while atomic mass is the weighted average of all isotopes.

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