# Avogadro Number Is

The number 6.02 × 10 23 is called Avogadro's number, the number of representative particles in a mole. It is an experimentally determined number. A representative particle is the smallest unit in which a substance naturally exists. For the majority of elements, the representative particle is the atom. Avogadro's number is defined as the number of elementary particles (molecules, atoms, compounds, etc.) per mole of a substance. It is equal to 6.022×1023 mol-1 and is expressed as the symbol NA. Avogadro's number is a similar concept to that of a dozen or a gross. A dozen molecules is 12 molecules. The Avogadro constant or (the Avogadro number earlier) is the number of elementary units in one mole of any substance. The Avogadro constant is denoted as NA. It has the dimension of the reciprocal amount of substance (mol −1). The approximate value of NA is 6.022 × 10 23 mol −1.

Jul 03, 2019 Avogadro's Number Problem Key Takeaways. Avogadro's number is 6.02 x 10 23. It is the number of particles in a mole. You can use Avogadro's number to convert between mass and the number of molecules of any pure substance. If you are given the mass of a sample (such as a snowflake), convert the mass to moles, and then use Avogadro's number to.

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## Avogadro's Number

### Avogadro's Number Is What

It certainly is easy to count bananas or to count elephants (as long as you stay out of their way). However, you would be counting grains of sugar from your sugar canister for a long, long time. Atoms and molecules are extremely small—far, far smaller than grains of sugar. Counting atoms or molecules is not only unwise, it is absolutely impossible. One drop of water contains about (10^{22}) molecules of water. If you counted 10 molecules every second for 50 years, without stopping, you would have counted only (1.6 times 10^{10}) molecules. Put another way, at that counting rate, it would take you over 30 trillion years to count the water molecules in one tiny drop.

### Avogadro's Number Fort Collins

Chemists of the past needed a name that could stand for a very large number of items. Amadeo Avogadro (1776-1856), an Italian scientist, provided such a number. He is responsible for the counting unit of measure called the mole. A **mole** (left( text{mol} right)) is the amount of a substance that contains (6.02 times 10^{23}) representative particles of that substance. The mole is the SI unit for amount of a substance. Just like the dozen and the gross, it is a name that stands for a number. There are therefore (6.02 times 10^{23}) water molecules in a mole of water molecules. There also would be (6.02 times 10^{23}) bananas in a mole of bananas, if such a huge number of bananas ever existed.

The number (6.02 times 10^{23}) is called **Avogadro's number**, the number of representative particles in a mole. It is an experimentally determined number. A **representative particle** is the smallest unit in which a substance naturally exists. For the majority of elements, the representative particle is the atom. Iron, carbon, and helium consist of iron atoms, carbon atoms, and helium atoms, respectively. Seven elements exist in nature as diatomic molecules and they are (ce{H_2}), (ce{N_2}), (ce{O_2}), (ce{F_2}), (ce{Cl_2}), (ce{Br_2}), and (ce{I_2}). The representative particle for these elements is the molecule. Likewise, all molecular compounds such as (ce{H_2O}) and (ce{CO_2}) exist as molecules and so the molecule is their representative particle. For ionic compounds such as (ce{NaCl}) and (ce{Ca(NO_3)_2}), the representative particle is the formula unit. A mole of any substance contains Avogadro's number (left( 6.02 times 10^{23} right)) of representative particles.

## Summary

- A mole of any substance contains Avogadro's number (left( 6.02 times 10^{23} right)) of representative particles.

## Contributors and Attributions

CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon.

Avogadro's number is the number of particles in one **mole** of any substance. Its numerical value is 6.02225 × 10^{23}. One mole of **oxygen** gas contains 6.02 × 10^{23}molecules of oxygen, while one mole of **sodium chloride** contains 6.02 × 10^{23}sodium ions and 6.02 × 10^{23} chloride ions. Avogadro's number is used extensively in calculating the volumes, masses, and numbers of particles involved in chemical changes.

The concept that a mole of any substance contains the same number of particles arose out of research conducted in the early 1800s by the Italian physicist Amedeo Avogadro (1776-1856). Avogadro based his work on the earlier discovery by Joseph Gay-Lussac that gases combine with each other in simple, whole-number ratios of volumes. For example, one liter of oxygen combines with two liters of **hydrogen** to make two liters of **water** vapor.

Avogadro argued that the only way Gay-Lussac's discovery could be explained was to assume that one liter of any gas contains the same number of particles as one liter of any other gas. To explain the water example above, he further hypothesized that the particles of at least some gases consist of two particles bound together, a structure to which he gave the name **molecule**.

The question then becomes, 'What is this number of particles in a liter of any gas?' Avogadro himself never attempted to calculate this. Other scientists did make that effort, however. In 1865, for example, the German physicist J. Loschmidt estimated the number of molecules in a liter of gas to be 2.7 × 10^{22}. The accepted value today is 2.69 × 10^{22}.

For all elements and compounds, not just gases, a given weight must contain a certain number of **atoms** or molecules. A weight (in grams) equal to the atomic or **molecular weight** of the substance-that is, one mole of any element or compound-must contain the same number of atoms or molecules, because there is always a constant relationship between atomic weights and grams. (One atomic **mass** unit = 1.66 × 10^{-22} g.) The number of atoms or molecules in one mole of an element or compound has been named Avogadro's number, in honor of his realization about the numbers of particles in gases. As stated above, that number has been determined to be 6.0225 × 10 ^{23}.

See also Atomic weight.

## Additional topics

### The Value Of Avogadro Number Is

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