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How To Calculate Atoms?

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Josh Bailey Profile
Josh Bailey answered
First you need to know the molecular formula for the molecule. Lets use water, H2O.
H has an atomic mass of 1, so H2 = 2
O has atomic mass of 16
16+2=18, which is the relative atomic mass of 1 water molecule (relative to a carbon 12 atom).
We must also know the mass of water, lets say 50g.
We can find the number of moles of water using the equation:
  Number of moles = mass/mass of 1 mole
  number of moles = 50/18 = 2.77777777777moles

Each mole of any substance contains 6.022x1023 molecules. So if we multiply 2.77777 by this number (avogadro's constant) then we get the number of molecules, =1.6727777x102
Now, since there are 3 atoms present in each water (2 hydrogen, 1 oxygen), we can find the total number of atoms by multiplying this answer by 3, = 5.018333x1024
If you mean the number of atoms in a single molecule, then you just need to know the molecular formula. I was assuming you meant for an amount of the molecule.
bob rich Profile
bob rich answered

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First you need to know the molecular formula for the molecule. Lets use water, H2O.
H has an atomic mass of 1, so H= 2
O has atomic mass of 16
16+2=18, which is the relative atomic mass of 1 water molecule (relative to a carbon 12 atom).
We must also know the mass of water, lets say 50g.
We can find the number of moles of water using the equation:
  Number of moles = mass/mass of 1 mole
  number of moles = 50/18 = 2.77777777777moles

Each mole of any substance contains 6.022x1023 molecules. So if we multiply 2.77777 by this number (avogadro's constant) then we get the number of molecules, =1.6727777x102
Now, since there are 3 atoms present in each water (2 hydrogen, 1 oxygen), we can find the total number of atoms by multiplying this answer by 3, = 5.018333x1024
If you mean the number of atoms in a single molecule, then you just need to know the molecular formula. I was assuming you meant for an amount of the molecule.

amber Jhon Profile
amber Jhon answered
The molecular formula of a compound describes the number of atoms or types of atoms present in one molecule of that compound. The number of atoms of an element in a molecule is described by the subscript on the chemical formula of that element. For example, the molecular formula for water is H2O. There are two atoms of hydrogen and one atom of oxygen are present in a water molecule. Similarly, the molecular formula for glucose is C6H12O6. Six atoms of carbon, twelve atoms of hydrogen and six atoms of oxygen are present in one molecule of glucose.

If a substance is given in moles, then according to Avogadro's number there are 6.022 x 1023 atoms present in one mole.

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