To find the amount of moles in 0.00032g of lithium, all you have to do is apply the formula n (moles) = m (mass, grams)/MM(molar mass). Molar mass is the atomic weight of the substance, and all you have to do is look at the periodic table. Lithium's is 6.94.
So, n (lithium) = 0.00032/6.94
n (lithium) = 0.000046 moles (2 d.p)
Take into account the number of atoms in the molecule for other calculations. Some elements are diatomic, which means they occur as two atoms of the same element bonded, such as hydrogen (H2) and chloride (Cl2). This means that to find moles of a substance such as Cl2, you need to multiply the molar mass by 2, since there are 2 atoms. Additionally, for compounds, you need to find the sum of all the elements involved's molar mass. For example, when you’re trying to find the moles in table salt, NaCl (sodium chloride), add the atomic weight of sodium and chlorine together for your molar mass.
Hope this helped!