To draw the Lewis structure for ClO3 (chlorate ion), we first count the valence electrons. Chlorine (Cl) has 7 valence electrons, and each oxygen (O) has 6 valence electrons. In total, ClO3 has:
Valence electrons: 7 (Cl) + 3 * 6 (O) = 25 electrons
Since ClO3 has a -1 charge, we add one more electron to the total, resulting in 26 valence electrons.
Next, we place the chlorine atom in the center and surround it with three oxygen atoms. To start forming bonds, we will use 6 electrons (3 bonds) to connect Cl to each of the three O atoms:
The structure begins as: Cl – O – O – O
After placing single bonds between Cl and each O, we need to distribute the remaining electrons to complete the octets of the oxygen atoms. Initially, each single bond will use 2 electrons, which accounts for 6 out of the 26. Therefore, we have 20 electrons left. Each oxygen needs a total of 8 electrons to complete its octet, so we will place 6 lone electrons on each of the three oxygens. This gives us:
Placed lone pairs: O: 6, O: 6, O: 6 (total 18 electrons used + 6 bonds = 24).
We still have 2 electrons left, which we can place on the central Cl atom as a lone pair, leading to a formal charge on the Cl atom. To minimize formal charges, we can turn one lone pair on one of the oxygens into a double bond:
This results in a structure where one oxygen is bonded with a double bond, and the others with single bonds:
O = Cl – O – O (where ‘=’ represents a double bond)
This gives us the finalized Lewis structure for ClO3.
Electron Pair Geometry Around the Central Atom
The electron pair geometry considers both bonding and lone pairs around the central atom. In this case, with one lone pair and three bonding pairs (from the single and double bonds), the electron pair geometry is ‘tetrahedral’.
Molecular Geometry Around the Central Atom
When only considering the bonded atoms, the molecular geometry is ‘trigonal pyramidal’ because the lone pair pushes the bonds down and gives it a pyramid shape instead of a flat one.
Bond Angles Around the Central Atom
The ideal bond angles for a tetrahedral arrangement are approximately 109.5 degrees. However, due to the lone pair affecting the molecular shape, the bond angles between the oxygen atoms will be slightly less than 109.5 degrees in this case, typically around 107 degrees.