What do the quantities "atomic number" and "mass number" represent?

The atomic number of a chemical element (aka its proton number) is the number of protons found in the nucleus of an atom of that element, and therefore identical to the number of the nucleus. The mass number tells us the number (the sum of nucleons) of protons and neutrons in the nucleus of an atom.

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.

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