Name: atomic mass and mole calculations
Uploaded: 2023-06-23T15:38:52.000Z
Duration: 1 min 25 s
Channel: JoVE

El peso atómico de un elemento, a veces llamado masa atómica, es aproximadamente igual a la suma del número de protones y neutrones. Esto se expresa en unidades de masa atómica, abreviado como amu, o Daltons, y se representa cerca de su símbolo químico en la tabla periódica.
Pero la mayoría de los elementos tienen varios isótopos que difieren en el número de neutrones y, por lo tanto, en sus masas.
Para tales elementos, el peso atómico es la masa promedio de todos los isótopos de un elemento, ponderada de acuerdo con su abundancia relativa o el porcentaje de cada isótopo que se encuentra en la naturaleza.
Por ejemplo, el cloro tiene dos isótopos naturales. La masa de cloro-35 es de 34,97 uma y la de cloro-37 es de 36,97 uma.
Cuando se multiplica por sus abundancias relativas, 75,77% para el cloro-35 y 24,23% para el cloro-37, y se suman, se obtiene el peso atómico final de 35,45 uma.
Dado que el cloro-35 es más abundante en la naturaleza que el cloro-37, el peso atómico del cloro es cercano a 35 uma.

peso atómico

Los protones y neutrones tienen aproximadamente la misma masa, alrededor de 1.67 × 10^-24 gramos. Los científicos definen arbitrariamente esta cantidad de masa como una unidad de masa atómica (uma) o un Dalton. Los electrones son mucho más pequeños en masa que los protones, pesando solo 9.11 × 10^-28 gramos, o aproximadamente 1/1800 de una unidad de masa atómica. Como resultado, no contribuyen mucho a la masa atómica general de un elemento. Esto significa que, al considerar la masa atómica, es costumbre ignorar la masa de cualquier electrón y calcular la masa del átomo basándose únicamente en el número de protones y neutrones.

Sin embargo, dado que la mayoría de los elementos que ocurren naturalmente están compuestos por isótopos, es importante considerar la masa y la abundancia natural de los isótopos al determinar la masa atómica de dichos elementos. La masa atómica en estos casos se calcula sumando las masas de todos los isótopos del elemento, cada uno multiplicado por su abundancia fraccional natural.

Los químicos a menudo usan la unidad "mol" para determinar el número de átomos de un compuesto que participan en una reacción química. Un mol de un elemento es su peso atómico en gramos, mientras que un mol de un compuesto es la suma de los pesos atómicos de sus componentes, llamado peso molecular. Un ejemplo frecuentemente utilizado es el cálculo de un mol de glucosa con la fórmula química C_6H_12O_6. El peso atómico del carbono (C) es de 12.011 gramos, y hay seis átomos de carbono en la glucosa para un peso atómico total de 72.066 gramos. Haciendo los mismos cálculos para el hidrógeno (H) y el oxígeno (O), el peso molecular de la glucosa es igual a 180.156 gramos.

Este texto se adapta parcialmente de <a href="https://openstax.org/books/biology-ap-courses/pages/2-1-atoms-isotopes-ions-and-molecules-the-building-blocks?query=atomic%20mass&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-idp140338797859808">Openstax, Biology for AP</a><a href="https://openstax.org/books/biology-ap-courses/pages/2-1-atoms-isotopes-ions-and-molecules-the-building-blocks?query=atomic%20mass&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-idp140338797859808">® </a><a href="https://openstax.org/books/biology-ap-courses/pages/2-1-atoms-isotopes-ions-and-molecules-the-building-blocks?query=atomic%20mass&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-idp140338797859808">courses. Section 2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks</a> and <a href="https://openstax.org/books/anatomy-and-physiology-2e/pages/2-4-inorganic-compounds-essential-to-human-functioning?query=mole&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-id1218107">Openstax, Anatomy and Physiology 2e, Section 2.4 Inorganic compounds Essential to Human Functioning</a>

Peso Atómico

Los protones y neutrones tienen aproximadamente la misma masa, aproximadamente 1,67 × 10-24 gramos. Los científicos definen arbitrariamente esta cantidad de masa como una masa atómica ...

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Atomic mass and mole calculations help explain how much matter is in atoms and compounds. Protons and neutrons have about the same mass, about 1.67 × 10 -24 grams. Scientists define that mass as one atomic mass unit, or amu, also called one Dalton.

Electrons are much lighter than protons. They weigh only 9.11 × 10 -28 grams, or about 1/1800 of an atomic mass unit. Because of that small mass, electrons do not add much to an element’s overall atomic mass. When chemists calculate atomic mass, they usually ignore electrons and use only the protons and neutrons.

Many naturally occurring elements are made of isotopes, which are atoms of the same element with different masses. For these elements, atomic mass must include each isotope’s mass and its natural fractional abundance. Chemists find this by adding the masses of all the isotopes after multiplying each one by how common it is.

Chemists also use the mole to count atoms and compounds in reactions. A mole of an element is its atomic weight in grams. A mole of a compound is the sum of the atomic weights of its parts, and that total is called the molecular weight. Glucose, C6H12O6, is a common example. Carbon has an atomic weight of 12.011 grams, and six carbons in glucose give 72.066 grams. Doing the same for hydrogen and oxygen gives glucose a molecular weight of 180.156 grams.

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Atomic Mass and Mole Calculations

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