Atomic Weight Calculator

Atomic Weight Formula:

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

Atomic Weight:

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1. What is Atomic Weight?

Atomic weight (also called relative atomic mass) is the average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element. It accounts for all the natural isotopes of an element and their proportions.

2. How Does the Calculator Work?

The calculator uses the atomic weight formula:

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

Where:

\( \text{Isotope Mass} \) — Mass of each isotope in atomic mass units (amu)
\( \% \text{Abundance} \) — Natural abundance percentage of each isotope
\( \sum \) — Sum of all isotope contributions

Explanation: The atomic weight is a weighted average where each isotope's mass is multiplied by its natural abundance percentage (divided by 100), and all values are summed together.

3. Importance of Atomic Weight

Details: Atomic weight is fundamental in chemistry for stoichiometric calculations, determining molar masses of compounds, and understanding chemical reactions. It appears on the periodic table for each element.

4. Using the Calculator

Tips: Enter each isotope's mass in atomic mass units (amu) and its natural abundance percentage. Click "Add Another Isotope" for elements with multiple isotopes. Ensure abundance percentages sum to approximately 100% for accurate results.

5. Frequently Asked Questions (FAQ)

Q1: Why isn't atomic weight a whole number?
A: Atomic weight is an average that accounts for different isotopes and their natural abundances, which rarely results in a whole number.

Q2: How is this different from mass number?
A: Mass number is the sum of protons and neutrons in a specific isotope (always a whole number), while atomic weight is the weighted average of all naturally occurring isotopes.

Q3: Why do some elements have atomic weights in brackets?
A: Brackets indicate the atomic weight is for the most stable isotope, as these elements have no stable isotopes and their compositions vary.

Q4: How often are standard atomic weights updated?
A: The IUPAC updates atomic weights biennially to reflect new measurements of isotopic abundances.

Q5: Can atomic weight vary in nature?
A: Yes, some elements (like lithium) show natural variation in isotopic composition, leading to slightly different atomic weights in different samples.