What is the lewis structure for 3I- and IO4-?
A) What is their molecular and electron geometry?
B) Are they polar or nonpolar?
The Correct Answer and Explanation is :
Lewis Structures:
- Iodide Ion (I⁻):
- The iodide ion (I⁻) consists of a single iodine atom with a negative charge. Iodine, being in group 17 of the periodic table, has 7 valence electrons. However, since it has a negative charge, it gains one additional electron, giving it a total of 8 valence electrons.
- The Lewis structure for I⁻ shows iodine with three lone pairs and a single negative charge.
- Lewis structure: I⁻ is depicted as an iodine atom (I) with three lone pairs of electrons and a single negative charge.
- Iodate Ion (IO₄⁻):
- The iodate ion (IO₄⁻) consists of one iodine atom surrounded by four oxygen atoms. The iodine atom is in group 17 and has 7 valence electrons, and each oxygen atom (group 16) has 6 valence electrons.
- The total number of valence electrons is calculated by adding up the electrons from iodine and oxygen. The iodine atom contributes 7 electrons, and the four oxygens contribute 24 electrons (6 electrons per oxygen). The negative charge adds one more electron.
- Thus, IO₄⁻ has 32 valence electrons to be placed in the structure.
- The Lewis structure involves the iodine atom forming single bonds with each of the four oxygen atoms. One of the oxygen atoms is double-bonded to iodine to satisfy the octet rule. The remaining oxygens are single-bonded to iodine, and lone pairs are added around the oxygen atoms.
- The overall charge is negative, so one of the oxygen atoms has an extra electron.
A) Molecular and Electron Geometry:
- Iodide Ion (I⁻):
- Electron Geometry: Since I⁻ is a single atom with no bonding partners, its electron geometry is linear.
- Molecular Geometry: The molecular geometry is also linear, as there are no bonds to form different shapes.
- Iodate Ion (IO₄⁻):
- Electron Geometry: The iodate ion has four regions of electron density (four bonds to oxygen), so its electron geometry is tetrahedral.
- Molecular Geometry: The molecular geometry of IO₄⁻ is also tetrahedral, as the four bonds to oxygen atoms do not have lone pairs on the iodine atom.
B) Polarity:
- Iodide Ion (I⁻):
- Polarity: The iodide ion (I⁻) is nonpolar. This is because it is a single atom with no bonds or molecular dipoles. The ion has a uniform charge distribution, making it nonpolar.
- Iodate Ion (IO₄⁻):
- Polarity: The iodate ion (IO₄⁻) is nonpolar. Despite having multiple oxygen atoms, the molecule is symmetrical. The tetrahedral arrangement of the oxygen atoms around the iodine atom leads to the cancellation of any potential dipoles. As a result, the net dipole moment of IO₄⁻ is zero, making it nonpolar.
Explanation (300 words):
In the case of the iodide ion (I⁻), its simple structure, consisting of a single iodine atom with three lone pairs and one negative charge, results in a nonpolar molecule. Iodine does not form any bonds or molecular dipoles since it is isolated as a single ion with a uniform charge distribution. The lack of any directional bond dipoles ensures that there is no overall molecular polarity, making I⁻ nonpolar.
For the iodate ion (IO₄⁻), the molecule exhibits tetrahedral electron and molecular geometry, with iodine centrally bonded to four oxygen atoms. The presence of the extra electron due to the negative charge does not disrupt the symmetry of the molecule. This symmetry leads to the cancellation of bond dipoles, as the four bonds to oxygen atoms are equally spaced around the iodine center. Even though the individual I–O bonds may have dipoles due to the electronegativity differences between iodine and oxygen, the overall symmetry of the molecule causes these dipoles to cancel each other out. As a result, the iodate ion is also nonpolar.
In summary, both the iodide ion and the iodate ion are nonpolar. The iodide ion lacks any molecular structure that would generate polarity, and the iodate ion, despite having multiple bonds, has a symmetrical structure that results in the cancellation of dipoles. Hence, both ions exhibit nonpolarity.