Chemistry: Atomic weight and atomic mass

Atomic mass is the total mass of protons and neutrons in an individual atom or isotope. Atomic weight is the average mass of all of the naturally-occurring isotopes of an element. Both atomic mass and atomic weight are represented using a unit called the atomic mass unit (​amu), which was defined using carbon's most common isotope, carbon-12.

Chemistry

Did you know that everything is made out of chemicals? Chemistry is the study of matter: its composition, properties, and reactivity. This material roughly covers a first-year high school or college course, and a good understanding of algebra is helpful.

Introduction to the atom

In chemistry, we will often be thinking about the world on a much smaller scale than you can see with the naked eye. Here we will learn about atoms and elements, tiny particles that make up the world around us. What are atoms, and what kind of properties do they have? How do we weigh and count atoms? We will answer those questions in this section!

Topic: Science

Learn about all the sciences, from physics, chemistry and biology, to cosmology and astronomy, across hundreds of videos, articles and practice questions.