Q. 4.113 - An Introduction to General, Organic, and Biological Chemistry

Question

There are four naturally occurring isotopes of Strontium: ${}_{38}{}^{84}Sr, {}_{38}{}^{86}Sr, {}_{38}{}^{87}Sr, and {}_{38}{}^{88}Sr$.

a. How many protons, neutrons, and electrons are in $Sr-87$?

b. What is the most abundant isotope in a Strontium sample?

c. How many neutrons are in $Sr-84$?

d. Why don't any of the isotopes of strontium have the atomic mass of $87.62 amu$ listed on the periodic table?

Step-by-Step Solution

Answer

a. In $Sr-87$ the number of protons and electrons is $38$ and number of neutrons is $49$.

b. ${}_{38}{}^{88}Sr$ is the most abundant isotope.

c. The number of neutrons in $Sr-84$ is $46$.

d. The isotopes of Strontium with mass $87.62 amu$ is not listed on the periodic table because of the weighted average.

Part (a) Step 1: Given Information

We need to find the number of protons, neutrons, and electrons in $Sr-87$.

Part (a) Step 2: Simplify

Using the basic representation of an atom, that is ${}_Z{}^{A}X$ in which $A=atomic mass$, $Z=atomic number$ and $X$ is atom.

So, in ${}_{38}{}^{87}Sr$ number of protons and electrons is $38$. And neutrons is $A-Z$,i.e.

$$\begin{gathered} Neutrons=87-38 \\ Neutrons=49 \end{gathered}$$

Part (b) Step 1: Given Information

We need to find the abundant isotope in the Strontium sample.

Part (b) Step 2: Explanation

To conclude the most prevalent Strontium isotope. First, compare the isotopes to the weighted average on the periodic table. As the Strontium has a weight average of $87.62 amu$, the most prevalent Strontium isotope is ${}_{38}{}^{88}Sr$.

Part (c) Step 1: Given Information

We need to find the number of neutrons in $Sr-84$.

Part (c) Step 2: Calculation

Calculating the number of neutrons in ${}_{38}{}^{84}Sr$.

$$\begin{gathered} Neutrons=A-Z \\ Neutrons=84-38 \\ Neutrons=46 \end{gathered}$$

Here, $A$ is the atomic number and $Z$ is the mass number.

Part (d) Step 1: Given Information

We need to explain the reason for the isotopes of strontium with an atomic mass of $87.62 amu$ is not listed on the table.

Part (d) Step 2: Explanation

The isotopes of the Strontium don't have an atomic mass of  $87.62 amu$ due to the said value being the weighted average of the atomic masses of all of its existing isotopes.