What is the mass for a single phosphorus atom in grams?

The only stable isotope of phosphorus is phosphorus-31. This means that the mass number of a phosphorus atom is 31 amu. The formula for converting amu into grams is: 1 Atomic Mass unit = 1.66053886 x 10-24 grams. So, to convert 31 amu to grams, do the following calculation:

31 amu x (1.66053886 x 10-24 g/1 amu) = 5.1 x 10-23 g*

*The answer is rounded to two significant figures because when multiplying or dividing, you round the answer to the fewest number of significant figures used in the calculation, which in this case is 31 with only two sig figs.