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 = 18 neutrons.

Hence atomic number = 18 Number of protons + neutrons = 18 + 22 = 40. Hence mass number = 40The chemical ... Take lithium for example. The diagram above shows each shell as a circle around the ...

which is based on atomic number rather than atomic mass. This arrangement was established by the British physicist Henry ...

For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus ...