Atomic Mass Unit and Carbon-12 Quiz

Study Notes

The Atomic Mass Unit Defined by Carbon-12

The atomic mass unit (AMU), also known as a dalton, is a fundamental unit used to express the masses of atoms, molecules, and subatomic particles. AMU is defined as one-twelfth the mass of a single carbon-12 (C-12) atom, which is approximately 1.660538921 x 10^(-24) grams.

Carbon-12 Overview

Carbon-12 is the most abundant carbon isotope, accounting for over 98% of naturally occurring carbon. It has 6 protons, 6 neutrons, and 6 electrons. C-12's atomic mass is exactly 12 AMU, making it a convenient reference point for atomic mass calculations.

Natural Abundance and Average Atomic Mass

Carbon, like many elements, has a few isotopes. C-12's natural abundance is around 98.89%, while the remaining 1.11% is C-13. The average atomic mass of carbon takes into account the natural abundance of both isotopes, with the AMU of carbon being approximately 12.011 AMU.

History of AMU Definition

The use of C-12 as the standard for atomic mass unit was adopted in 1961 to address confusion in the use of oxygen-16 as a reference. Atomic mass unit is now expressed as AMU, u, or Da, with AMU being the most common symbol.

In summary, the atomic mass unit is defined by the mass of a single C-12 atom, which is an essential reference point for understanding atomic masses of all elements. This definition has a long history, which has led to the widespread adoption of C-12 as a fundamental unit in chemistry and physics.

Description

Test your knowledge on the atomic mass unit (AMU) defined by Carbon-12, which serves as a fundamental reference point for expressing the masses of atoms, molecules, and subatomic particles. Learn about the natural abundance of Carbon-12, its average atomic mass, and the history of AMU definition.