Atomic Mass Of Elements 1-30

What is the Atomic Mass?

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

Atomic Mass, Atomic Weight and Relative Atomic Mass

Atomic mass, atomic weight and relative atomic mass denote related yet distinct concepts in chemistry:

Calculation of Atomic Mass

To calculate the atomic mass of an element, proceed as follows:

1. Identify the isotopes: Determine the various isotopes of the element and their respective masses.
2. Determine the relative abundance: Ascertain the percentage abundance of each isotope.
3. Multiply mass by abundance: Multiply the mass of each isotope by its relative abundance (expressed as a decimal).
4. Sum the values: Add the resulting values to obtain the atomic mass.

General Examples

Consider carbon, which has two stable isotopes: carbon‑12 and carbon‑13. The atomic mass of carbon is calculated based on the mass and abundance 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 possesses two common isotopes: chlorine‑35 and chlorine‑37. The atomic mass of chlorine is about 35.45 amu, reflecting the natural abundances of these isotopes.

Atomic Masses of Elements 1–30

The following table lists the atomic masses for elements with atomic numbers 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. In contrast, the atomic mass is the weighted average mass of all the isotopes of an element, taking into account their natural abundances.

Why is the atomic mass not an integer?

The atomic mass is not an integer because it represents the weighted mean of the masses of an element's isotopes, which have different masses and abundances.

How is the atomic mass measured?

The atomic mass is measured using mass spectrometry, which separates isotopes by their mass-to-charge ratio and quantifies their abundances.

Can the atomic mass of an element change?

Yes, the atomic mass can change if the relative abundances of an element's isotopes are altered by environmental factors or nuclear reactions.

Why is the atomic mass of carbon approximately 12.01 amu and not exactly 12?

The atomic mass of carbon 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.