Inorganic - Transition Metals Flashcards
What are the general physical properties of transition metals?
The elements from titanium to copper lie within the d-block elements.
Across a period, electrons are being added to a d-sub-level (3d in the case of titanium to copper). The elements from titanium to copper are metals. They are good conductors of heat and electricity. They are hard, strong, and shiny, and have high melting and boiling points.
These physical properties, together with fairly low chemical reactivity, make these metals extremely useful. Examples include iron (and its alloy steel) for vehicle bodies and to reinforce concrete, copper for water pipes, and titanium for jet engine parts that must withstand high temperatures.
What are the electronic configurations in the d-block elements?
In general, there are two outer 4s electrons and as you go across the period, electrons are added to the inner 3d sub-level. This explains the overall similarity of these elements.
These arrangements of chromium and copper do not quite fit the pattern. The d-sub-level is full in copper and half full in chromium and there is only one electron in the 4s outer level. It is believed that a half-full d-level makes the atoms more stable in the same way as a full outer main level makes the noble gas atoms stable.
When transition metal ions are formed, which electrons are lost first?
With all transition elements, the 4s electrons are lost first when ions are formed.
What is the definition of a transition element?
A transition metal is an element that has an incomplete d sub-shell in one of its common, stable ions (excluding Scandium).
What are the four main features that are common to all the transition metals?
- variable oxidation states
- coloured compounds
- catalysis
- formation of complexes
Why are variable oxidation states a chemical property of transition metals?
Transition metals have more than one oxidation state in their compounds, e.g. Cu(I) and Cu(II). They can therefore take part in many redox reactions.
Why is colour a chemical property of transition metals?
The majority of transition metal ions are coloured, e.g. Cu 2+ is blue.
Why is catalysis a chemical property of transition metals?
Catalysts affect the rate of reaction without being used up or chemically changed themselves. Many transition metals, and their compounds, show catalytic activity.
E.g. iron is the catalyst in the Haber process, vanadium oxide in the Contact process and manganese oxide in the decomposition of hydrogen peroxide.
Why is complex formation a chemical property of transition metals?
Transition elements form complex ions. A complex ion is formed when a transition metal ion is surrounded by ions or other molecules, collectively called ligands, which are bonded to it by co-ordinate bonds.
E.g. [Cu(H2O)6]2+ is a complex ion that is formed when copper sulphate dissolves in water.
What are ligands?
All transition metal ions can form co-ordinate bonds by accepting electron pairs from other ions or molecules. The bonds that are formed are co-ordinate (dative) bonds.
An ion or molecule with a lone pair of electrons that forms a co-ordinate bond with a transition metal is called a ligand. Some ligands are neutral and others have a negative charge.
What is a complex ion?
In some cases, two, four, or six ligands bond to a single transition metal ion. The resulting species is called a complex ion. They may have a positive charge or a negative charge.
What is the co-ordination number?
The number of co-ordinate bonds from ligands to the metal ion (determines the shape of the molecules).
How does the co-ordination number affect the shape of the complex ion?
- Ions with co-ordination number six are usually octahedral.
- Ions with co-ordination number four are usually tetrahedral.
- Some ions with co-ordination number four are square planar.
What are aqua ions?
If you dissolve the salt of a transition metal in water, e.g. copper sulphate, the positively charged metal ion becomes surrounded by water molecules acting as ligands. Normally there are six water molecules in an octahedral arrangement. Such species are called aqua ions.
What are uni/bi/multidentate ligands?
Unidentate: ligands that form one co-ordinate bond to a metal ion (e.g. :Cl-)
Bidentate: ligands that form two co-ordinate bonds to a metal ion (e.g. en)
Multidentate: ligands that form more than two co-ordinate bonds to a metal ion (e.g. porphyrin)
Multidentate ligands form complexes that are more stable than monodentate ligands.
Give examples of bidentate ligands (form two co-ordinate bonds).
- ethane-1,2-diamine, or 1,2-diaminoethane
- ethanedioate (oxalate) ion
- benzene-1,2-diol, or 1,2-dihydroxybenzene
What is EDTA 4-?
An important multidentate ligand is the ion ethylenediaminetetracetate, called EDTA 4-.
This can act as a hexadentate ligand using lone pairs on four oxygen and both nitrogen atoms.
What are chelates?
Complex ions with polydentate ligands are called chelates. Chelates can be used to effectively remove d-block metal ions from solution.
What is the chelate effect?
If you add a hexadentate ligand such as EDTA to a solution of a transition metal salt, the EDTA will replace all six water ligands in the aqua ion [Cu(H2O)6]2+ as shown:
[Cu(H2O)6]2+(aq) + EDTA 4-(aq) -> [CuEDTA]2-(aq) + 6H2O(l)
In this equation, two species are replaced by seven. This increase in the number of particles causes a significant increase in entropy which drives the reaction to the right. For this reason, chelate complexes with polydentate ligands are favoured over complexes with monodentate ligands and is called the chelate effect.
What do both ligand sites of bidentate ligands do?
Both ligand sites of bidentate ligands usually bond to the same metal forming a ring. However, they can act as bridges between two metal ions.
What are the shapes of complex ions?
- 6 ligands, octahedral, 90 degrees, most complexes with small ligands
- 4 ligands, tetrahedral, 109.5 degrees, with larger ligands (when ligands are too big for 6 to fit)
- 4 ligands, square planar, 90 degrees, Pt2+ and Ni2+ complexes (e.g. anti-cancer drug cis-platin)
- 2 ligands, linear, 180 degrees, Ag+ complexes (e.g. [Ag(NH3)2]+)
What complex ion does Tollen’s reagent contain?
[Ag(NH3)2]+ is a linear complex. A solution containing this complex ion is called Tollen’s reagent and is used in organic chemistry to distinguish aldehydes from ketones.
Aldehydes reduce the [Ag(NH3)2]+ to Ag (metallic silver), while ketones do not. The silver forms a mirror on the surface of the test tube.
What isomers can transition metal complexes form?
Isomers are compounds with the same molecular formula but with different arrangements of their atoms in space. Transition metal complexes can form both geometrical isomers (cis-trans, E-Z) and optical isomers.
How do transition metal complexes form geometrical isomers?
Here ligands differ in their position in space relative to one another.
This type of isomerism occurs in octahedral and square planar complexes. Ligands can be next to each other, or on opposite sides of the central ion.
A pair of geometrical isomers will have different chemical properties.