¿Que es la Masa Atómica?

Understanding Atomic Mass

Definition and Importance of Atomic Mass

• The atomic mass refers to the mass of atoms, which are too small to be weighed directly in grams. A relative atomic mass table was created using a new unit called the atomic mass unit (Uma).

• Atomic mass, sometimes referred to as atomic weight, is defined as the mass of an atom in atomic mass units (Uma). One Uma is equivalent to one-twelfth the mass of a carbon-12 atom.

Reference Isotope: Carbon-12

• Carbon-12 is chosen as a reference because it has 6 protons and 6 neutrons. This isotope is assigned a value of 12 atomic mass units due to its established significance by scientists.

• The weight of a carbon-12 atom is approximately 1.9927 x 10^-23 grams. Consequently, one Uma equals about 1.6606 x 10^-24 grams.

Average Atomic Mass Calculation

• In chemistry textbooks, atomic masses listed for elements are often close to the sum of their protons and neutrons. However, these values represent averages that account for isotopes—atoms with different masses.

• For example, copper has two isotopes: copper-63 and copper-65. Copper-63 is more abundant; thus, its average atomic mass is calculated at 63.55 Uma.

Implications of Isotope Abundance