Final answer:
The atomic number of oxygen (8) indicates that it has 8 protons, and in a neutral atom, also 8 electrons. This atomic number is constant across oxygen's isotopes, which differ by their number of neutrons: oxygen-16 has 8, oxygen-17 has 9, and oxygen-18 has 10 neutrons.
Step-by-step explanation:
The atomic number of an element, such as oxygen, provides valuable information about its structure. The atomic number indicates the number of protons in an atom's nucleus, which is a defining characteristic of the element. For instance, oxygen's atomic number is 8, meaning every atom of oxygen has 8 protons. In a neutral atom, the number of protons equals the number of electrons, so an oxygen atom also has 8 electrons.
When discussing isotopes, although all atoms of an element have the same number of protons, the number of neutrons can vary. The atomic number (8 for oxygen) remains constant across isotopes, but the mass number changes due to the different numbers of neutrons. Isotopes are denoted by their mass number, which is the sum of protons and neutrons in the nucleus. For oxygen, the three stable isotopes are oxygen-16 (8 protons, 8 neutrons), oxygen-17 (8 protons, 9 neutrons), and oxygen-18 (8 protons, 10 neutrons).