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

Il peso atomico di un elemento, a volte chiamato massa atomica, è approssimativamente uguale alla somma del numero di protoni e neutroni. Questo è espresso in unità di massa atomica, abbreviato in amu, o Daltons, ed è rappresentato vicino al suo simbolo chimico sulla tavola periodica.
Ma la maggior parte degli elementi ha diversi isotopi che differiscono nel numero di neutroni e quindi nelle loro masse.
Per tali elementi, il peso atomico è la massa media di tutti gli isotopi di un elemento, ponderata in base alla loro abbondanza relativa o alla percentuale di ciascun isotopo presente in natura.
Ad esempio, il cloro ha due isotopi presenti in natura. La massa del cloro-35 è di 34,97 amu e quella del cloro-37 è di 36,97 amu.
Moltiplicando per le loro abbondanze relative, 75,77% per il cloro-35 e 24,23% per il cloro-37, e sommando, si ottiene il peso atomico finale di 35,45 amu.
Poiché il cloro-35 è più abbondante in natura del cloro-37, il peso atomico del cloro è vicino a 35 amu.

peso atomico

I protoni e i neutroni hanno approssimativamente la stessa massa, circa 1,67 × 10-24 grammi. Gli scienziati definiscono arbitrariamente questa quantit? di massa come un'unit? di massa atomica (amu) o un Dalton. Gli elettroni sono molto pi? piccoli in massa rispetto ai protoni, pesando solo 9,11 × 10-28 grammi, o circa 1/1800 di un'unit? di massa atomica. Di conseguenza, non contribuiscono molto alla massa atomica complessiva di un elemento. Ci? significa che, considerando la massa atomica, ? consueto ignorare la massa di eventuali elettroni e calcolare la massa dell'atomo basandosi solo sul numero di protoni e neutroni.

 Tuttavia, poichla maggior parte degli elementi presenti naturalmente ? composta da isotopi, ? importante considerare la massa e l'abbondanza naturale degli isotopi quando si determina la massa atomica di tali elementi. La massa atomica in tali casi viene calcolata sommando le masse di tutti gli isotopi dell'elemento, ciascuno moltiplicato per la sua abbondanza frazionaria naturale.

 I chimici spesso utilizzano l'unit? "mole" per determinare il numero di atomi di un composto che partecipano a una reazione chimica. Una mole di un elemento ? il suo peso atomico in grammi, mentre una mole di un composto ? la somma dei pesi atomici dei suoi componenti, chiamata peso molecolare. Un esempio spesso utilizzato ? il calcolo di una mole di glucosio con la formula chimica C6H12O6. Il peso atomico del carbonio (C) ? di 12,011 grammi e ci sono sei atomi di carbonio nel glucosio per un peso atomico totale di 72,066 grammi. Effettuando gli stessi calcoli per l'idrogeno (H) e l'ossigeno (O), il peso molecolare del glucosio ? di 180,156 grammi.

 Questo testo ? in parte adattato da <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 atomico

Protoni e neutroni hanno approssimativamente la stessa massa, circa 1,67 × 10-24 grammi. Gli scienziati definiscono arbitrariamente questa quantità di massa come una massa atomica ...

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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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Atomic Mass and Mole Calculations

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