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9.8 The Chemistry of Art: 4. Transition Metals and electronic configurations

Syllabus reference (October 2002 version)
4. The chemical properties of the transition metals can be explained by their more complicated electronic configurations	Students learn to: identify the block occupied by the transition metals in the Periodic Table define the term transition element explain why transition metals may have more than one oxidation state account for colour changes in transition metal ions in terms of changing oxidation states explain using the complex ions of a transition metal as an example, why species containing transition metals in a high oxidation state will be strong oxidising agents	Students: process and present information from secondary sources by writing electron configurations of the first transition series in terms of sub-shells perform a first-hand investigation to observe the colour changes of a named transition element as it changes in oxidation state solve problems and process information from secondary sources to write half equations and account for the changes in oxidation state choose equipment, perform a first-hand investigation to demonstrate and gather first-hand information about the oxidising strength of KMnO₄

Extract from Chemistry Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.

[Edit: 27 Jun 08]

Prior Learning: Preliminary modules 8.3.2, 8.3.3, HSC module 9.2.4.

Background: Transition elements tend to be more uniform in their properties than main group elements in that they are all metals. However, while transition metals with lower oxidation states behave as metals (forming cations), when exhibiting their higher oxidation state they form covalent bonds often with oxygen. As electrons in the outer d-shell can absorb visible wavelengths of light, transition metals appear brightly coloured.

identify the block occupied by the transition metals in the Periodic Table

The transition metals occupy the d-block.

define the term transition element

Periods 4,5,6 and 7 incorporate the d-orbital transition elements. The general pattern is that the d orbitals are filled between the filling of the s and p orbitals.

explain why transition metals may have more than one oxidation state

One of the most characteristic chemical properties of the transition metals is the occurrence of multiple oxidation states.
The oxidation number refers to the number of electrons gained or lost by an atom or ion.
As the s and d subshell electrons are so close in energy, transition elements can involve all or most of these electrons in bonding. Therefore transition metals can form bonds by giving up more than one electron.
Ions with a charge of +2 are formed by loss of two s electrons. Oxidation states of above +2 involve loss of d electrons as well.
Transition metals and their oxidation states

Sc Ti V Cr Mn Fe Co Ni Cu Zn

+1 X

+2 X X X X X X

+3 X X X X

+4 X X

+5 X

+6 X

+7 X

X = common oxidation states

process and present information from secondary sources by writing electron configurations of the first transition series in terms of sub-shells

Elements of the
first transition series Electron
Configuration

scandium [1s²2s²2p⁶3s²3p ⁶]4s²3d¹

titanium [1s²2s²2p⁶3s²3p ⁶]4s²3d²

vanadium [1s²2s²2p⁶3s²3p ⁶]4s²3d³

chromium [1s²2s²2p⁶3s²3p ⁶]4s¹3d⁵

manganese [1s²2s²2p⁶3s²3p ⁶]4s²3d⁵

iron [1s²2s²2p⁶3s²3p ⁶]4s²3d⁶

cobalt [1s²2s²2p⁶3s²3p ⁶]4s²3d⁷

nickel [1s²2s²2p⁶3s²3p ⁶]4s²3d⁸

copper [1s²2s²2p⁶3s²3p ⁶]4s¹3d¹⁰

zinc [1s²2s²2p⁶3s²3p ⁶]4s²3d¹⁰

Note that chromium and copper have 4s¹ with, respectively, a half-filled 3d⁵ and filled 3d¹⁰ sub-shell. The d sub-shell energy level is lowest when half-filled or filled.

Elements of the first transition series	Electron Configuration
scandium	[1s²2s²2p⁶3s²3p ⁶]4s²3d¹
titanium	[1s²2s²2p⁶3s²3p ⁶]4s²3d²
vanadium	[1s²2s²2p⁶3s²3p ⁶]4s²3d³
chromium	[1s²2s²2p⁶3s²3p ⁶]4s¹3d⁵
manganese	[1s²2s²2p⁶3s²3p ⁶]4s²3d⁵
iron	[1s²2s²2p⁶3s²3p ⁶]4s²3d⁶
cobalt	[1s²2s²2p⁶3s²3p ⁶]4s²3d⁷
nickel	[1s²2s²2p⁶3s²3p ⁶]4s²3d⁸
copper	[1s²2s²2p⁶3s²3p ⁶]4s¹3d¹⁰
zinc	[1s²2s²2p⁶3s²3p ⁶]4s²3d¹⁰

perform a first-hand investigation to observe the colour changes of a named transition element as it changes in oxidation state

Choose a transition metal to investigate. One example could be chromium.

Transition Metal Chromium compound or ion Oxidation State Colour

chromium chromic oxide, Cr₂O₃ (Cr³⁺) +III green

chromate ion, in K₂CrO₄ (CrO₄ ^2-)
+VI

yellow

dichromate ion, in K₂Cr₂O₇ (Cr₂O₇ ^2-)
+VI

orange

The different oxidation states can be observed by the following method:

Prepare a solution of orange potassium dichromate.

Place 1 mL of the solution in a test tube and slowly add drop by drop 0.1M sodium hydroxide. The yellow colour produced indicates the presence of the chromate ion.

Addition of 0.1M HCl will change the solution back to orange dichromate.

Add 1mL of ethanol and gently warm. The solution will change to green Cr³⁺ ions.

Transition Metal	Chromium compound or ion	Oxidation State	Colour
chromium	chromic oxide, Cr₂O₃ (Cr³⁺)	+III	green
chromate ion, in K₂CrO₄ (CrO₄ ^2-)	+VI	yellow
dichromate ion, in K₂Cr₂O₇ (Cr₂O₇ ^2-)	+VI	orange

solve problems and process information from secondary sources to write half equations and account for the changes in oxidation state

You need information here on solving problems relating to half equations.

Change in Oxidation Number Half equation

chromium: +VI to +III Cr₂O₇^2-+ 14H⁺ + 6e^- 2Cr³⁺ + 7H₂O

manganese: +VII to +II

MnO₄^- + 8H⁺ + 5e^- Mn²⁺ + 4H₂O

iron: +III to +II

Fe³⁺ + e^- Fe²⁺

copper: +II to +I

Cu²⁺ + e^- Cu¹⁺

Change in Oxidation Number	Half equation
chromium: +VI to +III	Cr₂O₇^2-+ 14H⁺ + 6e^- 2Cr³⁺ + 7H₂O
manganese: +VII to +II	MnO₄^- + 8H⁺ + 5e^- Mn²⁺ + 4H₂O
iron: +III to +II	Fe³⁺ + e^- Fe²⁺
copper: +II to +I	Cu²⁺ + e^- Cu¹⁺

The change in oxidation state involves the d sub-shell electrons.

account for colour changes in transition metal ions in terms of changing oxidation states

Transition metal ions, have electrons in a partially filled d sub-shell. Electrons in lower energy orbitals can absorb visible wavelengths and move to slightly higher d orbitals. This accounts for the colour changes in the transition metal reactions.
The different colours for the oxidation states of a particular transition metal, simply indicate that different numbers of d or s subshell electrons have been removed forming the ions.

choose equipment, perform a first-hand investigation to demonstrate and gather first-hand information about the oxidising strength of KMnO₄

Some information about potassium permanganate is given below. Use this to plan a suitable first-hand investigation to perform to gather information about the oxidising strength of KMnO₄.
Choose the appropriate equipment for this investigation.
Gather information by setting out a result table to record the colour changes as they occur.

The table could be similar to the one below:

Compound/ion Colour

MnO₄ ^-

MnO₄ ^2-

MnO₂

Mn²⁺

Compound/ion	Colour
MnO₄ ^-
MnO₄ ^2-
MnO₂
Mn²⁺

Some useful information to assist you when doing this investigation.

Potassium permanganate is a powerful oxidising agent and is widely used as such in volumetric analysis. When heated with an alkali the purple permanganate (MnO₄ ^-) solution is reduced to green manganate (MnO₄^2-). If a reducing agent (Fe²⁺) is also present the manganate is reduced to brown manganese dioxide (MnO₂). In acid solutions the reduction proceeds further and light pink, almost colourless, Mn²⁺ forms.

explain using the complex ions of a transition metal as an example, why species containing transition metals in a high oxidation state will be strong oxidising agents

Transition metal elements in their highest oxidation state will combine with highly electronegative oxygen and fluorine.
Chromium forms the chromate and dichromate ions, while manganese forms the permanganate ion. These ions are important oxidising agents releasing oxygen. They will also oxidise halogen acids to free halogens.
Complex ions such as CrO₄^2-, Cr₂O₇^2- and MnO₄^- are strong oxidising agents (electron acceptors) because they contain many oxygen atoms. The oxygen atoms are able to readily accept electrons because most of these oxygen atoms have only six electrons in their outer shell.