Determine the chemical formula of the higher oxide that forms the element with atomic number 17.

In the Periodic Table of Elements D.I. Mendeleev at number 17 is the element – Chlorine. If we consider its electronic structure of the atom 1s ^ 2 2 ^ 2 2p ^ 6 3s ^ 2 3p ^ 5, then it is clear that at the last (third) energy level chlorine has 7 electrons. Therefore, the maximum oxidation state that a chlorine atom can exhibit is +7, and the formula for the higher oxide is Cl2O7.