If an element contains 12 positively charged, massive particles, then what is the element? Why is the atomic mass NOT equal to #12*"amu"#?

Question

If an element contains 12 positively charged, massive particles, then what is the element?  Why is the atomic mass NOT equal to #12*"amu"#?

Avery Adams · Accepted Answer

Well, if there are 12 nucular protons, then we gots magnesium isotopes....

Why? Because #Z=12# gives the element magnesium by definition. And magnesium has several isotopes....we could write...#""^24Mg#, #""^25Mg#, #""^26Mg#, which occur naturally in approx. #80%#, #10%#, #10%#, natural abundance.. And of course, the weighted average, #24.31*g*mol^-1#, is the mass we would use for the metal were we to use it as a reagent. #Mg^(2+)# is the standard cation....

Xavier Avery · Answer

undefined The element is magnesium (Mg), as it contains 12 positively charged, massive particles, which correspond to the number of protons in its nucleus.

The atomic mass is not equal to 12 atomic mass units (amu) because atomic mass takes into account both the mass and the abundance of isotopes of the element. Most elements have isotopes with different numbers of neutrons, resulting in a range of atomic masses. The atomic mass listed on the periodic table is the weighted average of the masses of all naturally occurring isotopes of the element, taking into account their relative abundances. Therefore, the atomic mass of magnesium may be slightly different from 12 amu due to the presence of isotopes with different masses and abundances.