The element calcium has the atomic number of 20 and the mass number of 40, how many neutrons does it have?
There are few simple rules to follow.
(1) The atomic number is equal to the number of protons.
(2) In neutrally charged elements, the number of electrons is the same as the number of protons.
Otherwise, positive charge means that the element lost an electron and negative charge means it gained an electron.
(3) The atomic mass is equal to the sum of the number of protons and number of neutrons.
So if you say that
40 = 20 + number of neutrons
40 - 20 = number of neutrons
number of neutrons = 20
An atom of the calcium-40 isotope has
Isotopes are named for their mass numbers, for example, carbon-14. The mass number of an isotope is the sum of the number of protons and neutrons in the atomic nucleus. The atomic number is the number of protons.
The calcium-40 isotope has a mass number of