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
