Oxygen-17 and oxygen-18 are not the same isotopes of oxygen. Isotopes are variations of an element that have the same number of protons but different numbers of neutrons. Oxygen-17 has 8 protons and 9 neutrons, while oxygen-18 has 8 protons and 10 neutrons. This difference in the number of neutrons gives oxygen-17 and oxygen-18 different physical and chemical properties. For example, oxygen-18 is slightly heavier than oxygen-17, and it has a different boiling point.