How many moles are equal to 1.2 x 1021 molecules of lithium?

1.2×1021.atoms Li=2.0×10−3.mol Li.

Lithium is a metal. It does not exist as molecules. We can, however, determine the moles equal to 1.2×1021 atoms of lithium.

1 mol atoms=6.022×1023 atoms

1.2×1021atoms Li×1mol Li atoms6.022×1023atoms Li=2.0×10−3mol Li (rounded to two significant figures)

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as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.