**Isotopes** represent atoms of an element that contain the **same atomic number** (same number of protons), but **different mass numbers** (different number of neutrons).

a. ^{35}**Cl is more abundant**

b. The average atomic mass of Cl is 35.45 amu.

Since **35.45 amu is closer to the mass of ^{35}Cl (35 amu)** than

We’re being asked to **percent ^{37}Cl**. We can use the following equation:

$\overline{){\mathbf{Atomic}}{\mathbf{}}{\mathbf{Mass}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}{\left[\mathbf{mass}\mathbf{\times}\mathbf{f}\mathbf{.}\mathbf{a}\mathbf{.}\right]}_{\mathbf{isotope}\mathbf{}\mathbf{1}}{\mathbf{+}}{\left[\mathbf{mass}\mathbf{\times}\mathbf{f}\mathbf{.}\mathbf{a}\mathbf{.}\right]}_{\mathbf{isotope}\mathbf{}\mathbf{2}}}$

where atomic mass = average atomic mass of the element and f.a. = fractional abundance of the isotope.

Chorline exists mainly as two isotopes ^{35}Cl and ^{37}Cl,

a) Which is more abundant?

b) How do you know?

c) Compute the percentage of chlorine that is the ^{37}Cl isotope.

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