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.

the MXene surface changes into a brush-like structure. Atoms of non-noble metals migrate out and form so-called "SAC-like structures" (single atom catalyst-like). These catalysts mediate two ...

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.