Atomic Number and Mass Number

[MedPR]

For some reason I really can't keep these straight in my head. There were a couple of related questions on the AAMC FL I took today and though I was able to reason through them and get them right, it took entirely too long for such a simple concept.

I was wondering if anyone had a mnemonic or some way that they remember which number is which (top or bottom) and which number represented what (protons, or proton+neutrons). I kind of doubt it since it's something so simple and basic, but I figured it was worth a shot.

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[Dasypus]

Atomic number = what kind of atom is this? Kinds of atoms are defined by number of protons, so atomic number = number of protons. This is the most basic fact about a given element (so basic it's sometimes left out, since if you know its letter, you should know its number), so it sits at the base of the letter.

Mass number = a decent approximation of the mass of an atom, in atomic mass units, because each proton and neutron weigh about one amu. So mass number = protons plus neutrons. It's right up at the top, because it's what you might not know about even if you've got the letter for the element (since you might have an isotope).

 

[MedPR]

Atomic number = what kind of atom is this? Kinds of atoms are defined by number of protons, so atomic number = number of protons. This is the most basic fact about a given element (so basic it's sometimes left out, since if you know its letter, you should know its number), so it sits at the base of the letter.

Mass number = a decent approximation of the mass of an atom, in atomic mass units, because each proton and neutron weigh about one amu. So mass number = protons plus neutrons. It's right up at the top, because it's what you might not know about even if you've got the letter for the element (since you might have an isotope).

Perfect. Thank you!