# Atomic ratio

*https://en.wikipedia.org/wiki/Atomic_ratio*

This article needs additional citations for
verification. (August 2015) |

The **atomic ratio** is a measure of the
ratio of atoms of one kind (i) to another kind (j). A closely related concept is the **atomic percent** (or **at.%**), which gives the percentage of one kind of atom relative to the total number of atoms.^{
[1]} The
molecular equivalents of these concepts are the **molar fraction**, or **
molar percent**.

## Atoms

Mathematically, the *atomic percent* is

- %

where *N*_{i} are the number of atoms of interest and *N*_{tot} are the total number of atoms, while the *atomic ratio* is

For example, the *atomic percent* of
hydrogen in
water (H_{2}O) is at.%_{H2O} = 2/3 x 100 ≈ 66.67%, while the *atomic ratio* of hydrogen to oxygen is *A*_{H:O} = 2:1.

## Isotopes

Another application is in
radiochemistry, where this may refer to **
isotopic ratios** or **
isotopic abundances**. Mathematically, the *isotopic abundance* is

where *N*_{i} are the number of atoms of the isotope of interest and *N*_{tot} is the total number of atoms, while the *atomic ratio* is

For example, the *isotopic ratio* of
deuterium (D) to
hydrogen (H) in
heavy water is roughly D:H = 1:7000 (corresponding to an *isotopic abundance* of 0.00014%).

## Doping in laser physics

In
laser physics however, the *atomic ratio* may refer to the **
doping ratio **or the **doping fraction**.

- For example, theoretically, a 100%
*doping ratio*of**Yb****:****Y**_{3}Al_{5}O_{12}is pure**Yb**_{3}Al_{5}O_{12}. - The
*doping fraction*equals,

## See also

## References

**^***McGraw-Hill Dictionary of Chemistry*. McGraw-Hill. 27 January 2003. pp. 31. ISBN 0-07-141046-5.