Atomic ratio explained

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

atomic percent ( i ) = (N _{i})/(N _{tot}) x 100 %where N_i are the number of atoms of interest and N_tot are the total number of atoms, while the atomic ratio isatomic ratio ( i:j ) = atomic percent ( i ) : atomic percent ( j ) .

For example, the atomic percent of hydrogen in water (H₂O) is, while the atomic ratio of hydrogen to oxygen is .

Isotopes

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

isotopic abundance ( i ) = (N _{i})/(N _{tot}) , 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 isisotopic ratio ( i:j ) = isotopic percent ( i ) : isotopic percent ( j ) .

For example, the isotopic ratio of deuterium (D) to hydrogen (H) in heavy water is roughly (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 : Y₃Al₅O₁₂ is pure Yb₃Al₅O₁₂.
• The doping fraction equals,

(N _{atoms of dopant})/(N _{atoms of solution which can be substituted with the dopant})

See also

• Table of concentration measures

Notes and References

1. Book: McGraw-Hill Dictionary of Chemistry. 27 January 2003. registration. McGraw-Hill. 0-07-141046-5. 31. 1.