Determine the number of protons, neutrons and electrons for the elements Al Na S.

1. The number of protons (p) and electrons (e) are equal, but opposite in sign, so that the charge of the atom is neutral.

2. The number of protons and electrons is equal to the ordinal number in the periodic table.

3. The number of neutrons (n) is equal to: the difference between the mass of the element and the serial number. They have no sign, because they are neutral.

Al – aluminum. Serial number 13. Weight – 27 (rounded up)

p = +13, e = -13, n = 27 – 13 = 14.

Na is sodium. Serial number 11, weight – 23.

p = +11, e = -11, n = 23 – 11 = 12.

S – sulfur. Serial number 16, weight – 32.

p = +16, e = -16, n = 32 – 16 = 16.