Atomic Mass of Elements 1-30

What Is Atomic Mass?

Atomic mass, also known as atomic weight, is the weighted average mass of an atom of an element based on the relative abundance of its isotopes. It is measured in atomic mass units (amu) and reflects the total number of protons and neutrons in an atom's nucleus.

Atomic Mass, Atomic Weight, and Relative Atomic Mass

Atomic Mass, Atomic Weight, and Relative Atomic Mass are related but distinct concepts in chemistry:

Calculating Atomic Mass

To calculate the atomic mass of an element, follow these steps:

1. Identify the Isotopes: Determine the different isotopes of the element and their respective masses.
2. Determine Relative Abundance: Find the percentage abundance of each isotope.
3. Multiply Mass by Abundance: For each isotope, multiply its mass by its relative abundance (expressed as a decimal).
4. Sum the Values: Add all the values obtained in the previous step to get the atomic mass.

Common Examples

Consider carbon, which has two stable isotopes: Carbon-12 and Carbon-13. The atomic mass of carbon is calculated based on the abundance and mass of these isotopes. If Carbon-12 has an abundance of 98.93% and Carbon-13 has an abundance of 1.07%, the atomic mass of carbon is approximately 12.01 amu.

Another example is chlorine, which has two common isotopes: Chlorine-35 and Chlorine-37. The atomic mass of chlorine is approximately 35.45 amu, reflecting the natural abundance of these isotopes.

Atomic Mass of Elements 1-30

The following table lists the atomic mass of elements with atomic numbers ranging from 1 to 30:

Frequently Asked Questions

What is the difference between atomic mass and atomic number?

The atomic number is the number of protons in an atom's nucleus, which defines the element. Atomic mass, on the other hand, is the weighted average mass of all the isotopes of an element, considering their natural abundance.

Why is atomic mass not a whole number?

Atomic mass is not a whole number because it is the weighted average of the masses of an element's isotopes, which have different masses and abundances.

How is atomic mass measured?

Atomic mass is measured using mass spectrometry, which separates isotopes based on their mass-to-charge ratio and measures their abundance.

Can atomic mass change for an element?

Yes, atomic mass can change if the relative abundance of an element's isotopes changes due to environmental factors or nuclear reactions.

Why is carbon's atomic mass approximately 12.01 amu instead of exactly 12?

Carbon's atomic mass is approximately 12.01 amu because it accounts for the presence of both Carbon-12 and Carbon-13 isotopes in nature, weighted by their natural abundances.