Question

From the abundances and atomic masses given in Appendix I of the two naturally occurring isotopes of boron. Determine the average atomic mass of natural boron. Compare this with the value given in the periodic table of Chapter 8.

Short answer

Atomic mass and average mass of boron both are equal to $10.811\text{u}$.

Step-by-step solution

Given data

Two major naturally occurring isotopes of boron are given as:

Atomic mass of boron-,$10$.$m_{\text{B}-10}=10.012937\text{u}$

Atomic mass of boron-,$11$ .$m_{\text{B}-11}=11.009305\text{u}$

$\%$Natural abundance boron-$10$is$19.9\%$.

$\%$Natural abundance boron- $11$is$80.1\%$ .

Atomic mass of boron in periodic table, $m_{\text{B}}=10.811\text{u}$.

Concept of Isotopes

Isotopes are members of a family of an element that all have the same number of protons but different numbers of neutrons.

Comparison of atomic mass and average mass of boron

The average atomic mass of boron is given as:

$\begin{array}{l}{m}_{\text{average}}=m_{B-10}\times 19.9\%+m_{B-11}\times 80.1\%\\ m_{\text{average}}=\left(10.012937\text{u}\right)\times 19.9\%+\left(11.009305\text{u}\right)\times 80.1\%\\ m_{\text{average}}=10.811\text{u}\end{array}$

Since, the atomic mass of boron in periodic table, $m_{\text{B}}=10.811\text{u}$.

On comparing the atomic mass and average mass of boron, one can say that both are equal to .$m_{\text{B}}=10.811\text{u}$