# Mole and Avogadro's Number explained

### Concept of Mole:

The mole is a unit of measurement. In fact, it is one of the important units of measurement in chemistry. It is a basic unit that measures the quantity or amount of a substance. Similarly, Avogadro's number is a fundamental constant in chemistry which enables students and teachers to compare the atoms or molecules of various substances with the mole as a quantitative unit. This was theorized by an Italian scientist named Amadeo Avogadro in 1811.

The mole is a crucial concept in chemical equations and calculations since the quantity of reactants and products are reflected in it, and must be balanced in both directions. This is explained via the equation below:

2H2(g) + O2(g) -> 2H2O(l)

From the above equation, the values in front of each reactants and product represents the mole. We can therefore state that two moles of hydrogen molecule reacts with one mole of oxygen molecule to produce two moles of water molecules. Meanwhile, understand that when no value is present in front of a reacting element, molecule or substance, one mole is attributed to it. This also holds true for one or more products.

You can read on Graham's law of diffusion here

The key point to note in the above paragraph is the fact that the concept of mole is attributed to the measurement of substances. In short, mole is often referred to as the amount of substance 'n'.

Note: Just as mass is expressed in grams and length in meter, the mole is expressed in 'mol' and it is a unit of measurement.

### Mole and Avogadro's Number

It is worthy of note to always understand that the mole of any substance is related to a constant called Avogadro's number. This Avogadro's number or constant is the number of particles (or atoms) contained in one mole of any substance. To make it clearer, think of it this way: 'one may choose to buy a cup of rice'. This 'cup' is the unit of measurement in this instance. However, the number of rice particles present in this cup will represent the Avogadro's number in that regard. So let's assume that one cup of rice will always contain ten thousand (10,000) rice particles. In this regard, for every cup of rice measured, we will have 10,000 rice particles inside it. Now, recall that atoms are the smallest particles of an element that can take part in a chemical reaction. With regards to quantitative measurements in chemistry, one mole of any substance will always contain 6.02214076 x 1023 particles within it. This number of particles contained in one mole of any substance is termed the Avogadro's number. Therefore, the mole may be referred to as the container (or cup in our above instance) while the number of atoms, particles or molecules it contains (rice in the above paragraph) is known as the Avogadro's number. This is the simplest summary of the relationship between the mole and Avogadro's number using a cup of rice as our instance.

You can read on elements and their characteristics here

Avogadro's number is defined as the number 6.02214076 × 1023 and it specifies the number of atoms, molecules or particles present in one mole of any substance. This number is also referred to as Avogadro's constant.

Understand that the number 6.02214076 × 1023 is also the number of atoms that was calculated to exist in exactly 12 grams of carbon-12. Interestingly, it turned out to be experimentally determined as the number of particles in one mole of any substance.

Just as 12 is a constant number (or value) for a dozen and 144 represents a constant value for gross, the Avogadro's number '6.02214076 x 1023' will always remain a constant value for one mole of any substance, be it an element, a molecule or a compound. This is summarized in the image below: Please read on Dalton's atomic theory and its modifications here

Importantly, it is noteworthy to state that regardless the elements, molecules or substance involved in measurement, one mole will always contain 6.02214076 x 1023 particles or atoms. For this reason, one mole of magnesium (Mg), one mole of water (H2O) and one mole of sodium chloride (NaCl) will still contain the same number of particles and that is 6.02214076 x 1023.

Recall that magnesium is an atom while water and sodium chloride are molecules respectively. However, sodium chloride can also be considered as a compound. Be that as it may, all are still weighted or quantified as one mole since no value is present in front of their respective chemical formula or symbol. With reference to our previous instance, this number of particles is a function of the 'measuring container or cup' (mole) which always has a constant amount of atoms or particles it can hold regardless whatever element, molecule or substance is within it.

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