What is the mass in grams of 4.00 1022 helium atoms?

To find the mass of 4.00 × 10²² helium atoms, first determine the number of moles of helium. Since one mole of helium contains approximately 6.022 × 10²³ atoms, you can calculate the number of moles:

[ \text{Moles of He} = \frac{4.00 \times 10^{22}}{6.022 \times 10^{23}} \approx 0.0664 \text{ moles} ]

Next, knowing that the molar mass of helium is about 4.00 g/mol, the mass can be calculated as:

[ \text{Mass} = 0.0664 \text{ moles} \times 4.00 \text{ g/mol} \approx 0.2656 \text{ g} ]

Thus, the mass of 4.00 × 10²² helium atoms is approximately 0.266 grams.