# What is the average atomic mass of gold if half of the gold found in nature has a mass of 197 amu and half has a mass of 198 amu?

Nov 25, 2015

The average atomic mass is $197.5$.

#### Explanation:

Multiply the mass of each isotope times its percentage as a decimal number and add the results. (50%)/100=0.5

$\text{average atomic mass} = \left(0.5 \times 197\right) + \left(0.5 \times 198\right) = 197.5$

Jan 13, 2016

The average atomic mass is 198.5 u.

#### Explanation:

Assume that you have 2 atoms of gold.

Then you have 1 atom of each isotope.

$\text{Mass of 1 Au-197 atom = 197 u}$
$\text{Mass of 1 Au-198 atom = 198 u}$
stackrel(———————————————)("Mass of 2 Au atoms"color(white)(Xl) = "395 u")

$\text{Average mass" = "395 u"/2 = "197.5 u}$