CH 101 1st Edition Lecture 9 Outline of Last Lecture I Review of Periodic Trends II Ionization Energy III Electronegativity Outline of Current Lecture I Electron configuration of ions II Oxidation states A The Six Rules of Oxidation III Predicting Oxidation Formulas IV Possible Oxidation States for Unknown Elements X Y and Z Current Lecture V Electron configuration of ions You already learned how to find the electron configuration of an element but why about ions To find the electron configuration of ions you take the configuration of the element and either subtracting in the case of a cation electrons from the orbitals in this order p s d f etc or adding in the case of a anion electrons starting with the lowest orbital If all of the valence electrons are subtracted or the orbital is filled you just write the noble gas that has the same amount of electrons isoelectronic Isoelectronic When two atoms have the same electron configuration they are isoelectronic For example Na1 and Ne are isoelectronic because they both have 10 electrons Ex What is the electron configuration s of the ion Zr2 Zr Kr 5s2 4d2 First find the electron configuration of the element These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Zr2 Kr 5s24d2 Zr2 is a cation that tells you Zr is losing 2 electrons take the two electrons from the orbitals in the given order p s d f since there is no p orbital in the noble gas electron configuration of Zr you take electrons from the s orbital Zr2 Kr 4d2 This is the correct electron configuration of the ion Zr2 Ex What is the electron configuration of the ion Se2 Se Ar 4s2 3d10 4p4 Find the electron configuration of the element first Se2 Ar 4s2 3d10 4p4 Look at the ion and determine that it is an anion Se is gaining 2 electrons Find the lowest orbital which is p and add 2 electron to it Se2 Ar 4s2 3d10 4p6 This configuration is the same at the noble gas Kr you can find this by going to Se on the periodic table and then counting two to the right for the two electron it gained you will see that you land on Kr Kr The electron configuration of the ion Se2VI Oxidation states Typically the elements in the main groups of the periodic table can have oxidation numbers that range from their group number to their group number minus 8 For example the oxidation state range for S is 6 to 2 because Sulfur is in main group 6 and 6 8 2 When it comes to transition metals they generally all have an oxidation number of 2 However the exceptions are that some groups tend to be 1 and others 3 just know that transition metals do not gain electrons the give them away B The Six Rules of Oxidation The six oxidation rules guide you toward finding the oxidation state by providing information on the pieces of the pieces of the molecule that make up the oxidation state Rule 1 The oxidation state of an element is always 0 F 0 H2 0 O8 0 Rule 2 The oxidation number of Fluorine F2 is always 1 Rule 3 The oxidation number of any element in Group 1 is always 1 K 1 Li 1 The oxidation number of any element in Group 2 is always 2 Ca 2 Ba 2 The oxidation number of Aluminum Al is always 3 Rule 4 The oxidation number of Hydrogen changes depending on who it bonds with a metal or a nonmetal When bonded to a metal the oxidation number of H is 1 When bonded to nonmetals its 1 Rule 5 The oxidation number of Oxygen O is always 2 Rule 6 The oxidation number of the elements in Group 17 halogens is most commonly 1 This rule is only used once all the other rules have been applied to the compound Ex What is the oxidation state of Bromine in the compound SrBr2 SrBr2 0 Start by setting up an equation oxidation state of Sr oxidation state of Br2 0 and set the equation equal to zero since the charge of the compound is 0 or neutral 2 0 See that Look at rule 3 it states that Group 2 will always have an oxidation state of 2 See that Sr is in Group 2 and solve the equation 2 2 0 Solve for Br by seeing that 2 2 0 Br2 2 meaning thatBr 1 This is the oxidation state for Br in the compound SrBr2 Ex What is the oxidation state of Cr in the compound Cr2O72 Cr2O72 2 The equation is not equal to 0 here because Cr2O72 is an anion with a charge of 2 2 7 2 Use rule 5 to tell you that the oxidation number for oxygen is 2 Multiply this number by the number of oxygen atoms in the compound to find the oxidation number for O 7 14 2 What 14 equals 2 You could find this by adding 2 and 14 to get 12 12 14 2 Now we know they oxidation number for Cr2 is 12 but what about for just one Cr atom Cr2 12 meaning that Cr 6 The oxidation number for Cr in the compoundCr2O72 is 6 VII Predicting Formulas You can predict formulas when you are looking at a compound made up of a metal and a nonmetal an ionic compound All you do is state the oxidation number of the group that the element is in and then criss cross the oxidation number with the other element s oxidation number and then simplify if you can Ex Predict the formulafor the compound formed between Ca S Ca2 S2 By looking at the periodic table you know that the oxidation state or charge of Ca is 2 and S is 2 Note that the cation always comes before the anion in a compound Ca2S2 Now bring the 2 that goes with Ca and bring it down to S and vice versa CaS The denominators are equal and can therefore be simplified Remember that an element can have many different oxidation states just because the oxidation state of Cl is 1 in the compound LiCl doesn t mean it is 1 in the compound NaClO in fact Cl has an oxidation state of 1 in this compound VIII Possible Oxidation States for Unknown Elements X Y and Z In this electron configuration chart you see that element Z have two electron in its outer shell element Y has 5 and element X has 6 The electron the element is willing to give away to create a positive oxidation state are circled The spaces where the element is wants to gain electrons to create a negative oxidation state are squared Using what you know about valence electron electronegativity and the periodic table try to describe these elements Element Z o Has a low ionization energy and electronegativity because it is far away from the nucleus …