All oxygen atoms have 8 protons and all sodium ... Note that you can work out the number of neutrons by subtracting the atomic number from the mass number. In this example, it is 35 – 17 ...

For example, the atomic number of sodium is 11. Every sodium atom has 11 protons and 11 electrons. It has 11 positive charges and 11 negative charges. The mass number of an atom is its total ...

which is based on atomic number rather than atomic mass. This arrangement was established by the British physicist Henry Moseley in 1913, who discovered that the atomic number (the number of ...