Figure (PageIndex1) shows that we require 2 hydrogen atoms and 1 oxygen atom to do 1 water molecule. If we want to make 2 water molecules, we will require 4 hydrogen atoms and also 2 oxygen atoms. If we desire to make 5 molecules of water, we need 10 hydrogen atoms and also 5 oxygen atoms. The proportion of atoms us will have to make any variety of water molecules is the same: 2 hydrogen atom to 1 oxygen atom.

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Figure (PageIndex1) Water Molecules. The ratio of hydrogen atoms to oxygen atoms used to do water molecule is constantly 2:1, no matter how countless water molecules room being made.

One problem we have, however, is the it is incredibly difficult, if no impossible, to organize atoms one in ~ a time. As declared in the introduction, we resolve billions of atoms at a time. How have the right to we store track that so many atoms (and molecules) in ~ a time? We do it by utilizing mass quite than by counting separation, personal, instance atoms.

A hydrogen atom has actually a massive of about 1 u. An oxygen atom has actually a massive of approximately 16 u. The proportion of the massive of one oxygen atom to the fixed of a hydrogen atom is therefore approximately 16:1.

If we have 2 atoms of every element, the proportion of their masses is around 32:2, i beg your pardon reduces to 16:1—the very same ratio. If we have actually 12 atom of each element, the proportion of their full masses is roughly (12 × 16):(12 × 1), or 192:12, which additionally reduces come 16:1. If we have actually 100 atoms of each element, the ratio of the masses is around 1,600:100, i m sorry again reduces come 16:1. As lengthy as we have actually equal numbers of hydrogen and oxygen atoms, the proportion of the masses will constantly be 16:1.

The exact same consistency is seen as soon as ratios the the masses that other aspects are compared. Because that example, the proportion of the masses the silicon atom to same numbers of hydrogen atom is constantly approximately 28:1, if the proportion of the masses of calcium atoms to equal numbers that lithium atoms is around 40:7.

So we have established that the masses of atoms are continuous with respect to each other, as long as we have actually the same variety of each form of atom. Consider a an ext macroscopic example. If a sample includes 40 g the Ca, this sample has the same number of atoms together there space in a sample of 7 g of Li. What us need, then, is a number the represents a convenient amount of atom so we can relate macroscopic amounts of substances. Clearly even 12 atoms are too few because atom themselves space so small. We require a number that represents billions and also billions the atoms.

mmsanotherstage2019.comists usage the hatchet mole to represent a big number of atom or molecules. Just as a dozen suggests 12 things, a mole (mol) to represent 6.022 × 1023 things. The number 6.022 × 1023, referred to as Avogadro’s number ~ the 19th-century mmsanotherstage2019.comist Amedeo Avogadro, is the number we use in mmsanotherstage2019.comistry to stand for macroscopic amounts of atoms and molecules. Thus, if we have actually 6.022 × 1023 O atoms, we say we have actually 1 mol that O atoms. If we have actually 2 mol of Na atoms, we have actually 2 × (6.022 × 1023) Na atoms, or 1.2044 × 1024 Na atoms. Similarly, if we have actually 0.5 mol of benzene (C6H6) molecules, we have actually 0.5 × (6.022 × 1023) C6H6 molecules, or 3.011 × 1023 C6H6 molecules.


Note

A mole to represent a very large number! If 1 mol of soldier were stack in a column, it can stretch earlier and forth in between Earth and also the sun 6.8 billion times.

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