so to calculate the average mass of lead with four isotopes with the neclues composition
one isotope with 82 protons and 122 neutrons at 1.37%
82p 124 n 26.26%
82p 125n 20.82%
82p 126n 51.55%
i've done a few of these i think the question was just phrased weird, and i don't remember how without the amu

so basically, you just find amu by adding proton and neutrons and then multiply the percentage the isotope makes up. then just sum them all:

(82+122)*0.0137 + (82+124)*.2626 + (82+125)*0.2082 + (82+126)*0.5155

No. Nevermind. The percentages do that.

This post was edited by CorinaMarie on Oct 6 2013 09:25pm