Atomic Mass Calculator
Calculate atomic mass, isotopic mass, and explore the relationship between atomic number and mass number
Understanding Atomic Mass
Atomic mass is the weighted average of all naturally occurring isotopes of an element. Our calculator helps you determine atomic mass, analyze isotopic contributions, and understand mass-related atomic properties.
Atomic Mass Calculator
Calculate weighted average atomic mass from isotopes
Understanding Atomic Mass
Atomic Mass
The weighted average mass of all naturally occurring isotopes of an element
- Measured in atomic mass units (amu)
- Considers isotopic abundance
- Found on periodic table
- Used in chemical calculations
Mass Number
The total number of protons and neutrons in an atom's nucleus
- Whole number value
- Different for each isotope
- Determines isotope identity
- Used in nuclear chemistry
Isotopic Distribution
The natural occurrence of different isotopes of an element
- Expressed as percentages
- Varies by element
- Affects average mass
- Determined experimentally
Frequently Asked Questions
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 considers both the mass and abundance of each isotope.
How is atomic mass calculated?
Atomic mass is calculated by multiplying each isotope's mass by its natural abundance (as a decimal), then summing these products. The result is the weighted average mass of the element.
What is an atomic mass unit (amu)?
An atomic mass unit (amu) is defined as exactly 1/12 the mass of a carbon-12 atom. This standard provides a convenient scale for expressing atomic and molecular masses.
Why do elements have different isotopes?
Isotopes are atoms of the same element with different numbers of neutrons in their nuclei. While they have the same number of protons (atomic number), their different neutron counts result in different mass numbers.
How does isotopic abundance affect atomic mass?
The natural abundance of isotopes determines their contribution to the element's average atomic mass. More abundant isotopes have a greater influence on the final weighted average.
Important Notes
- Atomic mass is measured in atomic mass units (amu)
- One amu is defined as 1/12 the mass of a carbon-12 atom
- Mass number is the sum of protons and neutrons
- Isotopes have the same atomic number but different mass numbers
- Natural abundance affects weighted average atomic mass
- Molecular mass is the sum of atomic masses in a molecule