Electronic configuration D-block transition metals (p54 lts) incomplete d subshell in at least one of their ions* lose 4s electrons before 3d electrons when form ions 4s orbitals filled before 3d orbitals except chromium ([Ar] 3d 5 4s 1 ) and copper ([Ar] 3d 10 4s 1 )

Oxidation States - rules for uncombined elements, the oxidation number is zero e.g. O in O 2 gas, metallic sodium. in polyatomic ions, the algebraic sum of all oxidation numbers must equal the charge on the ion. fluorine, in its compounds, has an oxidation number of -1. the algebraic sum of all oxidation numbers in a molecule must equal zero. usually oxygen has an oxidation number of -2 and hydrogen +1. Exceptions are peroxides (-1 for O) and metal hydrides (-1 for H). single atom ions, the oxidation state is the same as the charge on the ion e.g. Mg 2+ has an oxidation number of +2, I - is -1.

Transition metals 1.According to the Aufbau principle, are 3d or 4s orbitals occupied first? 2.Which 2 transition metals have electron configurations that do not follow 1. 3.What is the definition of a transition metal? 4.Which 2 metals aren’t technically transition metals? 5.Transition metals lose electrons firstly from which sublevel when forming ions? 6.What is the oxidation number of sulphur in SO32-? 7.In metal hydrides, what is hydrogen’s oxidation number? 8.What is the oxidation number of free elements?

Oxidation and reduction Increase in oxidation number - oxidation of the species has occurred e.g. SO 3 2- to SO 4 2- Compounds with metals in - high oxidation states tend to be oxidising agents - low oxidation states tend to be reducing agents Decrease in oxidation number - reduction of the species has occurred e.g. Cr 2 O 7 2- to Cr 3+

Variable oxidation states Transition metals exhibit variable oxidation states of differing stability +2 common oxidation state arising from loss of 4s electrons Different ions in different oxidation states have different stabilities (p58) Changes in oxidation state of transition metals often characterised by a distinct change in colour (p57) 3d subshells have similar energy levels to 4s so fairly easy to lose 3d electrons