posted by micheal on .
1. Need help Assigning oxidation numbers. Is it true that wehn looking at atoms in compounds from group 1 or 2 they are given the oxidization number which is the same as there charge example NaCl Na has an oxidization number of 1?
But is this also true for atoms in compounds which are from the 17 group exammple cacl2 cl has an oxidization number of -1 because it is found in the 17th group.
2. If a compound is given in which neither oxidization number is known is there charge automatically assighned exampple CN^- thank you.
Elements in Group 1 are assigned an oxidation number of 1. That is the same as the electrical charge on ions formed frm that group.
Elements in Group 17 (or Group VII-A) form ions with an electrical charge of -1. That is also their oxidation number in BINARY compounds like NaCl, SrBr2, etc.
In tertiary compounds like KClO3, NaOBr, etc., the Group 17 element is NOT assigned an oxidation number. That is calculated from the assigned oxidation numbers of the other two elements.
Finally, remember that elements in their "free" state are assigned an oxidation number of 0. In a formula of a compound like BaSO4, the sum of all the oxidation numbers is 0. In a polyatomic ion, the sum of the oxidation numbers is the ionic charge.
In simple monoatomic (1 atom) ions like Al^3+, Ba^2+, S^2-, etc., the oxidation number is the same as the electrical charge.