Chapter 6, Problem 59UTC

The chapter sections to review are shown in parentheses at the end of each problem.
a. How does the octet rule explain the formation of a magnesium ion? (6.1)
b. What noble gas has the same electron configuration as the magnesium ion?
c. Why are Group 1A (I) and Group 2A (2) elements found in many compounds, but not Group 8A (18) elements?

Interpretation Introduction

To explain: The formation of magnesium ion by octet rule.

Answer to Problem 59UTC

Solution: Magnesium loses two electrons for the formation of magnesium ion $\left({\text{Mg}}^{2+}\right)$ to get stable noble gas configuration.

Explanation of Solution

According to the octet rule, atoms either accept or lose electrons to acquire stable noble gas configuration or completing their octets. Octet means a full set of eight valence electrons.

The number of electrons an atom can accept or lose depends on the valence electrons present in its neutral state. After accepting or losing electrons it will form ions which can be positively or negatively charged.

In the case of magnesium atom, the electronic configuration of magnesium atom is $\left[\text{Ne}\right]\text{3s}²$ so magnesium atom can lose two electrons to form a stable noble gas configuration similar to the configuration of neon atom. It can also gain 6 electrons to form a noble gas configuration of Argon atom. The former requires fewer transfer of electrons, so, ${\text{Mg}}^{2+}$ is formed rather than ${\text{Mg}}^{6-}$ .

Conclusion

By the octet rule, ${\text{Mg}}^{2+}$ is more prevalent form of magnesium ion.

Interpretation Introduction

To determine: Which noble gas has the same electron arrangement as the magnesium ion.

Answer to Problem 59UTC

Solution: The noble gas that has the same electron arrangement as the magnesium ion is the neon gas with atomic symbol Ne.

Explanation of Solution

The electronic configuration of magnesium atom is as follows:

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}$

Magnesium ion is formed by losing two electrons the resultant electronic configuration will be:

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}$

This is also the electron configuration of noble gas, Neon with atomic symbol Ne.

Conclusion

The noble gas with the electron configuration of magnesium ion is Neon.

Interpretation Introduction

To Explain: The large amount of formation of compounds with elements of Group 1A(1) and Group 2A(2) but not Group 8A (18) elements.

Answer to Problem 59UTC

Solution: Group 1A (1) and Group 2A(2) elements are found to be more reactive than Group 8 A(18) elements because Group1A and Group 2A tend to lose electrons as they have 1 and 2 electrons respectively in their outermost orbital. They lose these electrons to obtain noble gas configuration as per the octet rule. Group 8A elements are un-reactive or inert in nature because they already have complete octet.

Explanation of Solution

All elements try to obtain 8 valence electrons in their outer shell as per the octet rule. Group 1A includes hydrogen, lithium, sodium, potassium, rubidium, cesium and francium. All these elements have one electron in their outermost shell, which they try to lose to obtain the noble gas configuration. Group 2A has beryllium, magnesium, calcium, strontium, barium and radium. All these elements have two electrons in their outermost shell, which they try to lose to obtain the noble gas configurations.

Group 8A elements are noble gas elements consisting of helium, neon, argon, krypton and xenon which have 8 electrons each in their valence shell, so they are very stable. Hence, they are usually not reactive in nature and are also knownas inert elements.

Conclusion

Group 1A and Group 2A elements are more reactive than Group 8A elements.