An element's atomic number defines it. An element with 17 protons will always be chlorine. However an element's mass numbers can vary, which means that it can have different numbers of neutrons.

IN a letter to NATURE of November 25 last Dr. Norman Campbell discusses the problem of the possible consistency of the assumptions about the motion and arrangement of electrons in the atom ...

The reaction releases a lot of heat as the ionic compound sodium chloride is formed. A sodium and chlorine atom are near each other. An electron from each atom feels the attraction from the other atom ...

The atoms in the reactants are: 1 calcium atom, 2 chlorine atoms, 2 sodium atoms, 2 hydrogen atoms, 2 carbon atoms, and 6 oxygen atoms The atoms in the products are: 1 calcium atom, 2 chlorine atoms, ...

(London and Toronto: Hodder and Stoughton, Ltd., 1923.) 2s. 6d. net. (2) The Atom and the Bohr Theory of its Structure: an Elementary Presentation. By H. A. Kramers Helge Holst. Translated from ...