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] 3d5 4s1)

and copper ([Ar] 3d10 4s1)

Oxidation States - rules• for uncombined elements, the oxidation number is zero

e.g. O in O2 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. Mg2+ 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. SO32- to SO4

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 occurrede.g. Cr2O7

2- to Cr3+

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 characterisedby a distinct change in colour (p57)

3d subshells have similar energy levels to 4s so fairly easy to lose3d electrons