calculate the mass of
1. an atom of copper
2. a molecule of CO2

1. Mass of 1 atom of copper :

1 mole of copper has mass  = 63.55 g
6.023 $\times$ 10²³ atoms of copper has mass = 63.55 g
1 atom of copper has mass = $\frac{63.55}{6.023\times {10}^{23}}=10.55 \times {10}^{-23} g$

2. Mass of  1 molecule of Carbon Dioxide :

1 mole of carbon dioxide has mass = 44 g
6.023 $\times$ 10²³ molecules of CO₂ has mass = 44 g
1 molecule of CO₂ has mass = 7.30 $\times$ 10^-23 g.