Name: mole, mass, and avogadro’s number
Uploaded: 2020-09-03T13:38:25.000Z
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NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.2.1

Molar Mass

Le tableau périodique donne la masse atomique moyenne de chaque atome. Cependant, les échantillons macroscopiques contiennent un nombre extrêmement important d'atomes. Par conséquent, il est essentiel d'utiliser une unité de comptage appelée numéro d'Avogadro.Le nombre d'Avogadro, exprimé par le symbole NA, est généralement rond à 6, 022 X 10^23. Sa valeur est égale au nombre d'atomes dans exactement 12 grammes de carbone pur-12 isotope. Le terme mole, abrégé mol, est utilisé pour décrire le nombre d'Avogadro, tout comme le terme familier, douzaine, est utilisé pour décrire une quantité de 12.Néanmoins, une douzaine d'articles différents peuvent peser différemment malgré le même nombre d'articles. De même, les moles d'éléments différents ont des masses différentes mais contiennent toujours le même nombre d'atomes. La masse en grammes d'une mole d'un élément est appelée la masse molaire, exprimée en grammes par mole.Sa valeur est numériquement équivalente à la masse atomique de l'élément. Par conséquent, la définition de la mole nous permet de compter les particules en les pesant. La masse molaire et le nombre d'Avogadro peuvent être utilisés comme facteurs de conversion.Cela peut être utilisé pour calculer le nombre d'atomes dans une barre de 5 grammes d'or. La masse molaire moyenne de l'or est de 196, 96 grammes par mol. Ainsi, pour convertir la masse en moles, divisez la masse de la barre par la masse molaire moyenne.Ensuite, multipliez le nombre de moles au nombre d'Avogadro pour obtenir le nombre d'atomes totaux dans l'échantillon. Donc, cette barre d'or contient 1, 529 x 10^22 atomes.

masse molaire

L'identité d'une substance est définie non seulement par les types d'atomes ou d'ions qu'elle contient, mais aussi par la quantité de chaque type d'atome ou d'ion. Par exemple, l'eau, H20, et le peroxyde d'hydrogène, H2O2, sont semblables en ce que leurs molécules respectives sont composées d'atomes d'hydrogène et d'oxygène. Cependant, comme une molécule de peroxyde d'hydrogène contient deux atomes d'oxygène, contrairement à la molécule d'eau, qui n'en a qu'un, les deux substances présentent des propriétés très différentes. 
 
 Les atomes et les molécules sont extrêmement petits. Par conséquent, pour mesurer leurs quantités macroscopiques, une unité scientifique standard est nécessaire. La mole est une unité de quantité semblable à des unités familières comme la paire, la douzaine, etc. Elle fournit une mesure spécifique du nombre d'atomes ou de molécules dans un échantillon de matière. La connotation latine du mot “ mole ” est “ grande masse ” ou “ gros morceau ”, ce qui est cohérent avec son utilisation comme nom pour cette unité. La mole fournit un lien entre une propriété macroscopique facilement mesurée, la grosseur de la masse, et une propriété fondamentale extrêmement importante, le nombre d'atomes, de molécules, etc. 
 
 Une mole d'une substance est la quantité dans laquelle il y a 6,02214076 × 1023 entités distinctes (atomes ou molécules). Ce grand nombre, commodément arrondi à 6,022 × 1023, est une constante fondamentale connue sous le nom de nombre d'Avogadro (Na) ou constante d'Avogadro en l'honneur du scientifique italien Amedeo Avogadro. Cette constante est correctement rapportée avec une unité explicite de “ par mole ”. 
 
 Conformément à sa définition comme unité de quantité, 1 mole de tout élément contient le même nombre d'atomes que 1 mole de tout autre élément. Les masses de 1 mole d'éléments différents, cependant, sont différentes, puisque les masses des atomes individuels sont radicalement différentes. La masse molaire d'un élément (ou d'un composé) est la masse en grammes de 1 mole de cette substance, une propriété exprimée en unités de grammes par mole (g/mol). 
 
 La masse molaire de toute substance est numériquement équivalente à son poids atomique ou au poids de sa formule en uma. Selon la définition de l'uma, un seul atome de carbone pèse 12 uma (sa masse atomique est de 12 uma). Une mole de carbone pèse 12 g (12 g C = 1 mol atomes C = 6,022 &times 1023 atomes C) et la masse molaire du carbone est de 12 g/mol. Cette relation est valable pour tous les éléments puisque leurs masses atomiques sont mesurées par rapport à celle de la substance de référence de l'uma, le carbone 12. En étendant ce principe, la masse molaire d'un composé en grammes est également équivalente numériquement à la masse de sa formule en uma. Par exemple, l'hélium a une masse atomique de 4,002 uma et une masse molaire de 4,002 g/mol. 
 
 Alors que la masse atomique et la masse molaire sont numériquement équivalentes, gardez à l'esprit qu'elles sont très différentes en termes d'échelle. Pour que vous puissiez vous rendre compte de l'énormité de la mole, considérez une petite goutte d'eau pesant environ 0,03 g. Bien que cela ne représente qu'une minuscule fraction de 1 mole d'eau (~18 g), elle contient plus de molécules d'eau qu'on ne peut l'imaginer. Si les molécules étaient réparties de la même façon entre les sept milliards de personnes sur terre, chaque personne recevrait plus de 100 milliards de molécules d'eau. 
 
 La mole définit la relation entre la masse et le nombre d'atomes. Cela permet de calculer le nombre d'atomes en utilisant des formes appropriées du facteur de conversion : 1 mole d'atomes = 6,022 × 1023 atomes. Pour convertir entre eux la masse d'un élément (en grammes) et le nombre de moles, la masse molaire de l'élément (g/mol) est utilisée comme facteur de conversion. 
 
 Texte adapté d' <a href="https://openstax.org/books/chemistry-2e/pages/3-1-formula-mass-and-the-mole-concept">Openstax Chemistry 2e, Section 3.1 : Masse de la formule et le concept de mole.</a>

Masse molaire

L’identité d’une substance est définie non seulement par les types d’atomes ou d’ions qu’elle contient, mais aussi par la quantité de chaque type d’atome ou d’ion. Par exemple...

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mole, mass, and avogadro’s number

The mole links mass and the number of particles in a substance. It gives chemists a standard way to count atoms and molecules in samples that are far too small to see. It also helps show why substances with the same kinds of atoms can still have very different properties, like water, H2O, and hydrogen peroxide, H2O2.

The mole is an amount unit, like a pair or a dozen. One mole contains 6.02214076 × 10^23 discrete entities, such as atoms or molecules. This number is usually rounded to 6.022 × 10^23 and is called Avogadro’s number, or the Avogadro constant, named for Amedeo Avogadro. The constant is written with the unit per mole.

One mole of any element contains the same number of atoms as one mole of any other element. The masses are different, though, because atoms have different individual masses. That is why one mole of one element does not weigh the same as one mole of another element.

Molar mass is the mass in grams of one mole of a substance. It is reported in grams per mole, or g/mol. The molar mass of an element or compound is numerically equal to its atomic mass or formula mass in amu. For example, carbon has an atomic mass of 12 amu, so 1 mole of carbon has a mass of 12 g and a molar mass of 12 g/mol.

This same relationship works for other elements and for compounds. Helium, for example, has an atomic mass of 4.002 amu and a molar mass of 4.002 g/mol. Although the numbers match, atomic mass and molar mass are very different in scale.

A tiny drop of water can still contain an enormous number of molecules. A drop that weighs about 0.03 g is only a small part of 1 mole of water, which is about 18 g. Even so, it holds more water molecules than can easily be imagined. If those molecules were shared equally among the roughly seven billion people on Earth, each person would still get more than 100 billion molecules of water.

The mole also lets scientists convert between mass and amount. Using the relationship 1 mole of atoms = 6.022 × 10^23 atoms, the number of atoms can be calculated from a sample. The molar mass of an element is also used as a conversion factor to move between grams and moles.

Mole, Mass, and Avogadro’s Number

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molar mass

The mole links mass and the number of particles in a substance. It gives chemists a standard way to count atoms and molecules in samples that are far too small to see. It also helps show why substances with the same kinds of atoms can still have very different properties, like water, H2O, and hydrogen peroxide, H2O2. The mole is an amount unit, like a pair or a dozen. One mole contains 6.02214076 × 10^23 discrete entities, such as atoms or molecules. This number is usually rounded to 6.022 ×...

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Learn how the mole connects mass, atoms, and molecules through Avogadro’s number and molar mass, with clear examples for high school chemistry.

Mole, Mass, and Avogadro’s Number | JoVE K12

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Structure And Properties Of Matter

Quantifying matter

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Stoichiometry

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Mole, Mass, and Avogadro’s Number

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