What is the mass in grams of 9.76 Ã 1012 atoms of naturally occurring lithium?

1) Convert 9.76 * 10^12 atoms into mole.

To do that, divide by Avogagro's number:

(9.76 * 10 ^ 12 atoms) / (6.022 * 10 ^ 23 atoms / mole) = 1.62 * 10 ^ - 11 mole

2) Multiply the number of moles by the atomic mass of Lithium

mass = number of moles * atomic mass = 1.62 * 10 ^ - 11 moles * 6.9 g / mol

mass = 11.2 * 10 ^ - 11 g = 1.12 * 10^ - 10 g

Answer: 1.12 * 10 ^ - 10 g