Atomic mass

Atomic mass is a fundamental concept in chemistry and physics, referring to the mass of an individual atom. It is usually expressed in atomic mass units (amu), where 1 amu is approximately equal to the mass of a single proton or neutron.

Definition

The atomic mass of an atom is the mass of an atom at rest and is typically expressed in atomic mass units. The atomic mass is an experimental property of an atom. It is determined to a large extent by the number of protons and neutrons in the atomic nucleus, but also includes the mass of the electron cloud surrounding the nucleus.

Measurement

The atomic mass is not measured directly. Instead, it is calculated from the masses of isotopes and their relative abundances. The most common method for measuring the atomic mass of an atom is by using a mass spectrometer.

Atomic Mass and Atomic Weight

While the terms atomic mass and atomic weight are often used interchangeably, they do not mean the same thing. The atomic mass refers to the mass of a single atom, which can be a specific isotope. On the other hand, atomic weight refers to the weighted average of the atomic masses of an element's isotopes.

Atomic Mass Unit

The atomic mass unit (amu) is a standard unit of mass that quantifies mass on an atomic or molecular scale. One atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom, the isotope of carbon with six protons and six neutrons.

Importance in Chemistry

The atomic mass is a critical property of an atom that influences its behavior in chemical reactions. For example, the atomic mass determines the amount of an element that will react with a given amount of another element. It also influences the physical properties of elements and compounds, such as density and boiling point.

See Also

• Isotope
• Atomic number
• Periodic table
• Molar mass