An oxygen atom has 8 electrons. This is because the atomic number of oxygen is 8, which means it has 8 protons in its nucleus, and in a neutral atom, the number of electrons is equal to the number of protons. The electronic configuration of oxygen is 1s22s22p41s^22s^22p^41s22s22p4, meaning it has two electrons in the first shell and six electrons in the second shell, with a total of 8 electrons. The valence shell of oxygen contains 6 electrons, which are involved in chemical bonding.