The atomic number of oxygen is 8. This means that an oxygen atom has 8 protons in its nucleus.
The atomic number of an element is defined as the number of protons in the nucleus of an atom. It is a fundamental property of an element and determines its unique identity. Each element has a specific atomic number, and it is used to arrange the elements in the periodic table.
The atomic weight of an element, on the other hand, is the average mass of the atoms of that element, taking into account the different isotopes and their relative abundances. Oxygen has multiple isotopes, such as oxygen-16, oxygen-17, and oxygen-18, which have different numbers of neutrons. These isotopes occur in different proportions in nature.
The atomic number of an element is not directly equal to the atomic weight because the atomic weight considers all the isotopes and their abundance. However, for elements with a single dominant isotope, the atomic weight can be very close to the atomic number.
In the case of oxygen, the most abundant isotope is oxygen-16, which accounts for more than 99% of natural oxygen. Oxygen-16 has 8 protons and 8 neutrons, resulting in an atomic weight of approximately 16. Oxygen-17 and oxygen-18, which are less abundant isotopes, contribute to the small deviation from the atomic number.
In nature, the different isotopes of an element are formed through various processes, such as nuclear reactions in stars, supernovae, and cosmic ray interactions. These processes create and distribute different isotopes throughout the universe. Over billions of years, these isotopes mix and become part of the materials that make up the Earth and its atmosphere. Therefore, the atomic weight of an element reflects the average abundance of its isotopes as they naturally occur on Earth.