Oxygen-16: 8 protons, 8 neutrons, 8 electrons
Oxygen-18: 8 protons, 10 neutrons, 8 electrons
Using atomic and mass numbers, we can find information about the makeup of atoms.
Protons
Every element has a unique number of protons, and every atom of the same element will have the same number of protons. This means that both oxygen atoms must have the same number of protons. The number of protons in an element is equal to its atomic number. Since oxygen has an atomic number of 8, all oxygen atoms will have 8 protons. This means that oxygen-16 and oxygen-18 have 8 protons.
Neutrons
The number of neutrons an atom of a certain element can have varies. Atoms of the same element that have different numbers of neutrons are known as isotopes. The number of neutrons can be found through the mass number. The mass number is the number that follows the dash in the name of the isotope. This number is equal to the protons plus the neutrons. So, to find the number of neutrons in an oxygen atom, subtract 8 protons from the mass number. This means oxygen-16 has 8 neutrons and oxygen-18 has 10 neutrons.
Electrons
Remember that electrons are negatively charged, protons are positively charged, and neutrons have no charge. The number of electrons in an atom determines the charge of the atom. If the number of electrons equals the number of protons, then the charge of the atom will equal 0. If there are more electrons, then the atom will be negatively charged and vice versa. Since neither of the atoms has any indication of a nonzero charge, the number of electrons must equal the number of protons. So, both oxygen atoms have 8 electrons.
