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jacob193

Answer:

The relative abundance of each hydrogen isotope determines the weight of that isotope's mass in the average atomic mass of this element.

Explanation:

The isotopes of an element are atoms with

  • the same number of protons (same atomic number, same element,) but
  • a different number of neutrons.

Since the number of neutrons per nucleus varies, the mass of these isotopes are different from each other.

These isotopes occur at different percentages in nature. The percentage of one single isotope in a sample is called the abundance of that isotope. The average atomic mass of an element is a weighted average of the mass of all its naturally-occurring isotopes. The exact weight of each isotope depends on its relative abundance.

On the earth in nature,

  • around [tex]99.98\%[/tex] of all hydrogen nuclei are [tex]^{1}\rm H[/tex] (with a relative atomic mass of approximately 1.007825.)
  • around [tex]0.02\%[/tex] of all hydrogen nuclei are [tex]^{2}\rm H[/tex] (with a relative atomic mass of approximately 2.014102.)

Isotopes that are heavier than [tex]^{2}\rm H[/tex] do exist, but only in trace amounts. Their relative atomic mass barely influence the average atomic mass of hydrogen.

The average relative atomic mass of hydrogen will thus be:

[tex]\underbrace{1.007825}_{\text{relative}\atop \text{mass of}~^{1}\rm H}\times 99.98\% + \underbrace{2.014102}_{\text{relative}\atop \text{mass of}~^{2}\rm H}\times 0.02\% \approx 1.008[/tex].

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