Consider the periodate (IO4-) anion. What is the central atom? Enter its chemical symbol. How many lone pairs are around the central atom? What is the ideal angle between the iodine-oxygen bonds? ° Compared to the ideal angle, you would expect the actual angle between the iodine-oxygen bonds to be …
The Correct Answer and Explanation is:
Central atom: I
Lone pairs on central atom: 0
Ideal bond angle: 109.5°
Actual bond angle: the same as
Explanation
To determine the properties of the periodate anion (IO4-), we first use the VSEPR (Valence Shell Electron Pair Repulsion) model, which begins with its Lewis structure.
The central atom is iodine (I), as it is the least electronegative element and there is only one of it. Next, we calculate the total number of valence electrons. Iodine (Group 17) contributes 7, each of the four oxygen atoms (Group 16) contributes 6 (for a total of 24), and the negative charge adds 1 extra electron. This gives a total of 7 + 24 + 1 = 32 valence electrons.
When drawing the Lewis structure, iodine is placed at the center, bonded to the four oxygen atoms. While several resonance structures exist to minimize formal charge (involving double bonds and an expanded octet for iodine), VSEPR theory simplifies this by treating single, double, or triple bonds as single electron domains. In every valid resonance structure of periodate, the central iodine atom is bonded to four oxygen atoms and has no non-bonding valence electrons.
Therefore, the central iodine atom has four electron domains around it, all of which are bonding pairs. There are zero lone pairs on the central atom.
According to VSEPR theory, a central atom with four electron domains and no lone pairs (an AX4 configuration) will have a tetrahedral electron geometry and a tetrahedral molecular geometry. The ideal bond angle for a perfect tetrahedral shape is 109.5°.
Bond angle deviation typically occurs when lone pairs on the central atom exert a stronger repulsive force than bonding pairs, compressing the angles between bonds. However, in the periodate ion, there are no lone pairs on the central iodine atom. Furthermore, all the terminal atoms are identical (oxygen), meaning the repulsive forces between the four identical iodine-oxygen bonds are perfectly symmetrical and balanced. Consequently, the molecule maintains a perfect tetrahedral geometry, and the actual bond angles are not distorted. They remain the same as the ideal angle of 109.5°.
