Question

What is the mass of lead atoms?

Answer 1

-The atomic mass is the weighted average of all of the isotopes of that element, in which the mass of each isotope is multiplied by the abundance of that particular isotope.
-Atomic mass is also referred to as atomic weight, but the term “mass” is more accurate.

Complete step by step answer:
The atomic mass of an element is the average mass of the atoms of an element measured in atomic mass unit $amu$, also known as Dalton's $D$.
For instance it can be determined experimentally that neon consists of three isotopes: neon- $20$(with $10$ protons and $10$ neutrons in its nucleus) with a mass of $19.992amu$ and in abundance of $90.40$ whereas, neon- $21$ which has a mass of $20.944amu$ and an abundance of $0.27$, and the neon- $22$ (with $10$ protons and $12$ neutrons) with a mass of $21.991amu$ and an abundance of $9.25$ . the average atomic mass of neon is
$0.9048\times 19.992amu=18.09amu$
$0.0027\times 20.994amu=0.057amu$
$0.0925\times 21.991amu=2.03amu$
Total mass $=20.18amu$
Similarly, we got the mass of lead ( $Pb$ ) atom to follow the above procedure in order to get $207.2amu$.
The four stable isotopes of lead are $^{204}Pb$ , $^{206}Pb$ ,$^{207}Pb$ and $^{208}Pb$, with abundances $1.4$, $24.1$ , $22.1$ and $52.4$ respectively, which combine in order to give a value of standard atomic weight as $207.2amu$.

Note: The original periodic table of the elements published by Dimitri Mandeleev in $1869$ arranged the elements that were known at that time in order of increasing atomic weights, since this was prior to the discovery of nucleus and the interior structure of the atom.
-The atomic mass of an element can be calculated by taking the sum of masses of all the isotopes of that element and their specific abundances in nature.