[VISUAL] 8. Based on the diagram above, which of the following best helps to explain why MgO(s) is n — Bonding Chemistry Question

STEPS:

1. Understand the prerequisite for electrical conductivity: For any substance to conduct electricity, it must satisfy two conditions: it must contain charged particles (such as ions or electrons), and those charged particles must be free to move (mobile) so they can migrate under the influence of an electric field.
2. Identify the bonding and species in magnesium oxide (MgO): Magnesium oxide is an ionic compound formed from a metal and a nonmetal. It does not consist of neutral molecules; instead, it is composed of charged magnesium cations ($\text{Mg}^{2+}$) and oxide anions ($\text{O}^{2-}$) held together by strong electrostatic attractions (ionic bonds).
3. Analyze the structure of solid magnesium oxide, $\text{MgO}(s)$:
* As illustrated in the "Solid MgO" diagram, the $\text{Mg}^{2+}$ and $\text{O}^{2-}$ ions are tightly locked in a highly organized, rigid three-dimensional crystalline lattice.
* Because these strong electrostatic forces hold the ions in fixed positions, the charged ions cannot move or flow. Consequently, $\text{MgO}(s)$ is unable to conduct electricity.
4. Analyze the structure of molten/liquid magnesium oxide, $\text{MgO}(l)$:
* As shown in the "Liquid MgO" diagram, when MgO is heated to its melting point, the rigid crystalline lattice is disrupted.
* In the liquid state, the attractions between ions are partially overcome, allowing the $\text{Mg}^{2+}$ and $\text{O}^{2-}$ ions to freely move and slide past one another.
* Because these charged ions are now mobile, they can flow toward electrodes to carry an electrical current.
5. Conclude the correct option: The solid holds ions in a fixed lattice, whereas the liquid state allows these same ions to move freely and conduct electricity, matching Option D.

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WHY_OTHERS_WRONG:

• Option A is incorrect: Ionic compounds do not contain free, delocalized electrons in either the solid or liquid state. In both phases, valence electrons are highly localized on the oxide ions. Electrical conductivity in a molten ionic compound is due to the mobility of the ions themselves, not free electrons (which is the mechanism for metals).
• Option B is incorrect: Liquid magnesium oxide ($\text{MgO}(l)$) is a pure molten liquid at an extremely high temperature (melting point $\approx 2852^\circ\text{C}$). It contains no water; water would instantly vaporize at these extreme temperatures.
• Option C is incorrect: MgO is an ionic network compound and does not contain discrete, covalent "MgO molecules" in either phase. It consists entirely of separate $\text{Mg}^{2+}$ and $\text{O}^{2-}$ ions.