Question

Chlorine has two natural isotopes, chlorine-35 and chlorine-37.

Answer 1

Answer:

The relative atomic mass of chlorine depends on the ratio between the abundance of these two naturally-occurring isotopes.

Explanation:

The relative atomic mass of an element is a weighted average of the atomic mass of its naturally-occurring isotopes. The relative abundance of each isotope gives its weight in this weighted average.

For these two naturally-occurring isotopes of chlorine:

• The relative atomic mass of $^{35}{\rm Cl}$ is approximately $34.969$ daltons. The relative abundance of this isotope in nature is approximately $0.758$.
• The relative atomic mass $^{37}{\rm Cl}$ is approximately $36.966$ daltons. The relative abundance of this isotope in nature is approximately $0.242$.

$\begin{array}{|c|c|c|}\cline{1-3} \text{Isotope} & \text{Atomic Mass} & \text{Relative Abundance}\\ \cline{1-3} ^{35}{\rm Cl} & \approx 34.968\; \rm Da} & \approx 0.758 \\ \cline{1-3} ^{37}{\rm Cl} & \approx 36.966\; \rm Da & \approx 0.242 \\ \cline{1-3}\end{array}$.

$\begin{aligned}&\text{relative atomic mass of Cl} \\ &= \text{atomic mass of ^{35}{\rm Cl} } \times \text{relative abundance of ^{35}{\rm Cl} } \\&\quad + \text{atomic mass of ^{37}{\rm Cl} } \times \text{relative abundance of ^{37}{\rm Cl} } \\ &\approx 34.968\; \rm Da \times 0.758 + 36.966\; \rm Da \times 0.242 \\ &\approx 35.45\; \rm Da \end{aligned}$.

The relative abundance of $^{35}{\rm Cl}$ is much higher than that of $^{37}{\rm Cl}$. Consequently, the relative atomic mass of the element $\rm Cl$ is closer to the atomic mass of $^{35}{\rm Cl}\!$ than that of $^{37}{\rm Cl}\!$.