Question

Why the mass of 1 atom of hydrogen 1.6*10^-24?

Answer 1

You need your periodic table for this, as well as Avogadro's Number of 6.022x1023, which represents one mole of something (in this case, atoms). The periodic table gives you atomic weight.  Almost every periodic table will have this information on it somewhere.  The numbers you should see are: Hydrogen (element #1) = 1.008 Oxygen (element #8) = 16.00 These numbers are either in atomic mass units (amu), or in grams per mole of atoms.  This means that 1 MOLE of hydrogen atoms will weigh 1.008 grams.  That said, to find the mass of one ATOM, we need to convert from moles to atoms as follows: 1.008 grams/mole Hydrogen * (1 mole/6.022x1023 atoms) = 1.67 x 10-24 grams16.00 grams/mole Oxygen * (1 mole/6.022x1023 atoms) = 2.66 x 10-23 grams Any slight differences are due to the accuracy used for the atomic mass and/or Avogadro's Number.