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

O peso atômico de um elemento, às vezes chamado de massa atômica, é aproximadamente igual à soma do número de prótons e nêutrons. Isso é expresso em unidades de massa atômica, abreviado como amu, ou Daltons, e é representado próximo ao seu símbolo químico na tabela periódica.
Mas, a maioria dos elementos tem vários isótopos que diferem no número de nêutrons e, portanto, em suas massas.
Para esses elementos, o peso atômico é a massa média de todos os isótopos de um elemento, ponderada de acordo com sua abundância relativa ou a porcentagem de cada isótopo encontrado na natureza.
Por exemplo, o cloro tem dois isótopos naturais. A massa do cloro-35 é de 34,97 amu e do cloro-37 é de 36,97 amu.
Quando multiplicado por suas abundâncias relativas, 75,77% para cloro-35 e 24,23% para cloro-37, e somado, obtém-se o peso atômico final de 35,45 amu.
Como o cloro-35 é mais abundante na natureza do que o cloro-37, o peso atômico do cloro é próximo a 35 amu.

peso atômico

Prótons e nêutrons têm aproximadamente a mesma massa, cerca de 1,67 × 10-24 gramas. Os cientistas definem arbitrariamente essa quantidade de massa como uma unidade de massa atômica (u.m.a), ou um Dalton. Os elétrons possuem uma massa muito menor, quando comparados aos prótons, pesando apenas 9,11 × 10-28 gramas, ou cerca de 1/1800 de uma unidade de massa atômica. Como resultado, eles não contribuem muito para a massa atômica geral de um elemento. Isso significa que, ao considerar a massa atômica, é costume ignorar a massa de quaisquer elétrons e calcular a massa do átomo com base no número de prótons e nêutrons apenas.

No entanto, como a maioria dos elementos encontrados na natureza são compostos por isótopos, é importante considerar tanto a massa quanto a abundância natural desses isótopos ao se determinar a massa atômica desses elementos. A massa atômica nesses casos é calculada somando as massas de todos os isótopos do elemento, cada um multiplicado por sua abundância natural fracionária.

Os químicos frequentemente usam a unidade "mol" para determinar o número de átomos de um composto que participam de uma reação química. Um mol de um elemento é o seu peso atômico em gramas, enquanto um mol de um composto é a soma dos pesos atômicos de seus componentes, chamado de peso molecular. Um exemplo frequentemente usado é o cálculo de um mol de glicose com a fórmula química C_6H_12O_6. O peso atômico do carbono (C) é de 12,011 gramas, e existem seis carbonos na glicose, resultando em um peso atômico total de 72,066 gramas. Realizando os mesmos cálculos para hidrogênio (H) e oxigênio (O), o peso molecular da glicose é igual a 180,156 gramas.

Este texto foi parcialmente adaptado 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 Atômico

Prótons e nêutrons têm aproximadamente a mesma massa, cerca de 1,67 × 10-24 gramas. Os cientistas definem arbitrariamente essa quantidade de massa como uma massa atômica ...

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Anatomy and Physiology

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Fundamentals of Chemistry

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Atomic Weight

atomic mass and mole calculations

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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O JoVE Core Anatomia e Fisiologia apresenta detalhes anatômicos e fisiológicos do corpo humano em animações  abrangentes, claras e envolventes. Esta coleção de vídeos se concentra nas estruturas, componentes, funções e requisitos do corpo humano. É complementada por vídeos de cientistas em ação que demonstram a aplicação desse conhecimento em instalações médicas e de pesquisa do mundo real.

Atomic Mass and Mole Calculations

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