eli5 why do some elements on the periodic table have atomic weights with decimals and others don’t?

Question

eli5 why do some elements on the periodic table have atomic weights with decimals and others don’t?

In: 3

Answer 1

Lots of good insights here. At a higher level I’d add that numbers/quanta are inherently ‘imperfect or imprecise’ as it relates to explaining most fundamental physical/natural concepts, e.g., π going on ‘forever’. They’re an applied science (and the best we can do within the limits of our understanding).