Why is chlorine the central atom in a chlorate ion

  1. I know that when you draw the lewis structure for chlorate, the chlorine goes in the center with the oxygen bonded to it. What I don't understand is that the teacher told me that the central atom is the element with the fewest valence electrons. So wouldn't that make oxygen the central atom?
    This is what I think:
    Is it because the Group 7 elements are the most electronegative so when given a compound where there is 1 of the Group 7 element and 2 or more of elements in the other groups, then the Group 7 element will always be central?
  2. jcsd
  3. Try posting your question in the HW/Cousework section. You may get better results there.
  4. DrDu

    DrDu 4,113
    Science Advisor

    In most cases, the central atom will have a lower electronegativity than the ligands.
    This is true with metal ions, which have less valence electrons than typical ligands like oxygen etc, but it is also true for chlorine as electronegativity decreases down one column in the periodic system. Nevertheless there are exceptions also to this rule, e.g. in organophosphorus componds where some alkyl function acts as a ligand.
  5. So the reason why chlorine is the central atom is because it has a lower electronegativity than oxygen?
  6. I wouldn't say that's the reason as such, more that it's been shown that all the oxygens are equivalent, and for that to be the case, the chlorine has to be in the middle. Whether this is at the right level of answer may depend on the level of the question.
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