Draw the Lewis Structure for the permanganate ion. Based on its Lewis dot structure can you explain its solubility in water, ethanol, and cyclohexane?
The correct answer and explanation is :
Lewis Structure of the Permanganate Ion (( \text{MnO}_4^- )):
- Determine the total number of valence electrons:
- Manganese (Mn) is in group 7, so it has 7 valence electrons.
- Oxygen (O) is in group 6, so each oxygen atom has 6 valence electrons. Since there are 4 oxygen atoms, this gives ( 4 \times 6 = 24 ) electrons.
- The ion has a charge of -1, which means it has one extra electron.
- Total valence electrons = 7 (Mn) + 24 (O) + 1 (charge) = 32 valence electrons.
- Arrange the atoms:
- The central atom is Mn, with 4 oxygen atoms arranged around it. Mn is in the center because it can form more bonds due to its larger size and ability to accommodate more electrons.
- Distribute electrons to form bonds:
- Each oxygen will form a single bond with Mn, which uses 8 electrons (4 bonds × 2 electrons).
- The remaining 24 electrons will be placed as lone pairs on the oxygen atoms.
- Each oxygen gets 2 lone pairs (4 electrons) to complete its octet.
- Check for formal charges:
- The Mn atom typically forms a +7 oxidation state in the permanganate ion. To achieve this, Mn will have 7 bonds (one with each oxygen), and the overall charge on the ion will be -1.
Final Lewis Structure:
- Mn is in the center, surrounded by four oxygen atoms with single bonds.
- The oxygen atoms have lone pairs of electrons to complete their octets.
- The overall structure has formal charges of +7 on Mn and -1 on the ion.
Solubility Explanation:
In Water:
The permanganate ion (( \text{MnO}_4^- )) is highly soluble in water due to its ionic nature. Water is a polar solvent, meaning it has partial positive and negative charges. The ( \text{MnO}_4^- ) ion can interact with water molecules through ion-dipole interactions. The negative charge on the permanganate ion is attracted to the partial positive charges of water’s hydrogen atoms, facilitating dissolution.
In Ethanol:
Ethanol is less polar than water but still has some polar characteristics due to the hydroxyl group (-OH). As a result, the permanganate ion is somewhat soluble in ethanol, but the solubility is lower than in water. The ethanol molecules can interact with the permanganate ion, but these interactions are weaker compared to water’s stronger ion-dipole interactions.
In Cyclohexane:
Cyclohexane is a nonpolar solvent. The permanganate ion is very poorly soluble in cyclohexane because there are no strong interactions between the ion and the nonpolar cyclohexane molecules. Since there is no significant dipole-dipole or ion-induced dipole attraction, the solubility is negligible.
In summary, the solubility of ( \text{MnO}_4^- ) is highest in water, lower in ethanol, and very low in cyclohexane, primarily due to the nature of the solvents and the strength of interactions with the permanganate ion.