Chemistry

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1. Atomic Number

   • Number of PROTONS in the nucleus in an atom.

2. Mass Number

   • Number of PROTONS + the number of NEUTRONS.

3. Nucleon Number

   • Number of NEUTRONS + number of PROTONS.

4. Relative Atomic Mass/ Ar

   • This applies to atoms on their own, the weighted average mass of an atom relative/compared to the mass of 12C/ 12Carbon where 12C has a mass of 12.

5. Molecule Mass/Mr

   • This applies to molecules only, the Mr is the mass of a molecule compared to the mass of 12C where 12C has a mass of 12. A molecule has an Mr that is equal to the Ar's of all the atoms added together.

6. Relative formula mass/Mr

   • Same thing as Molecule Mass. The Mr is the mass of an ionic compound or ion or molecule compared to the mass of 12C, where 12C has a mass of 12. The Mr e.g. of NaCl is 35.5+23=58.5