1. **State the problem:** We need to find the total weight of an oxygen atom, which consists of 8 protons, 8 neutrons, and 8 electrons. Each particle has a given mass in grams. 2. **Given data:** - Mass of one proton = $1.67 \times 10^{-24}$ grams - Mass of one neutron = $1.68 \times 10^{-24}$ grams - Mass of one electron = $9.11 \times 10^{-28}$ grams - Number of protons = 8 - Number of neutrons = 8 - Number of electrons = 8 3. **Formula:** Total mass = (number of protons $\times$ mass of proton) + (number of neutrons $\times$ mass of neutron) + (number of electrons $\times$ mass of electron) 4. **Calculate each component:** - Protons: $8 \times 1.67 \times 10^{-24} = 13.36 \times 10^{-24}$ - Neutrons: $8 \times 1.68 \times 10^{-24} = 13.44 \times 10^{-24}$ - Electrons: $8 \times 9.11 \times 10^{-28} = 72.88 \times 10^{-28}$ 5. **Convert electron mass to the same power of ten as protons/neutrons:** $72.88 \times 10^{-28} = 0.7288 \times 10^{-24}$ 6. **Sum all masses:** $$13.36 \times 10^{-24} + 13.44 \times 10^{-24} + 0.7288 \times 10^{-24} = (13.36 + 13.44 + 0.7288) \times 10^{-24} = 27.5288 \times 10^{-24}$$ 7. **Express in proper scientific notation:** $$27.5288 \times 10^{-24} = 2.75288 \times 10^{-23}$$ 8. **Final answer:** The weight of an oxygen atom is approximately $2.75 \times 10^{-23}$ grams.