Topic 15 Transition metals

They sit in the middle of the periodic table Some of these elements are transition metals. The ones you mainly need to know are the top row of the block

It is a d block element that can form at least 1 stable ion with a partially filled subshell The d sub shell can hold up to 10 electrons. For period 4 elements, only 8 of them are transition metals. Scandium and zinc aren’t transition elements. This is because they don’t form a stable ion with a partially filled d sub shell In the configuration, you can see that they fill up singly first then double up. This is because electrons repel each other Chromium and copper behave differently. An electron from the 4s orbital moves into the 3d orbital to create a more stable half full or full 3d sub shell

Scandium and zinc aren’t transition metals Scandium forms only one stable ion of Sc3+ Sc3+ has an empty d subshell. As it is not partially filled it is not a transition element Zinc forms only 1 stable ion of Zn2+ Zn2+ has a full d - subshell. As it is not partially filled it is not a transition element

They lose from the 4S subshell first then 3D

Variable oxidation state, form coloured ions in solution and are good catalysts Transition metals have variable oxidation states. This is because the electrons sit in 4s and 3d energy levels which are very close. As a result, electrons are gained and lost using a similar amount of energy when they form the ions seen in the right of the table They also form coloured ions in solution.

V2+ is violet V3+ is green VO^2+ is blue VO2 + is yellow Cr3+ is green / violet - Violet when surrounded by 6H2O. They are normally substituted so look green Cr2O7 2- is orange Fe2+ is pale green Fe3+ is yellow Co2+ is pink Cu2+ is blue Don’t need to know Ti, Mn or Ni

Another property of transition metals is their ability to form complex ions A complex ion is where a central transition metal ion is surrounded by ligands bonded by dative covalent bonds You have a central metal atom. It is surrounded by ligands. These have at least 1 lone pair of electrons where they are used to form a dative covalent bond with the metal. A square bracket shows the full complex and the overall charge of the complex sits outside of this

It is an ion, atom or molecule that has at least one lone pair of electrons. They can be monodentate, bidentate or polydentate.

Ligands which only have 1 LP are called monodentate ligands. H2O NH3 CL- OH-

Ligands which have 2 LP’s pf electrons are called bidentate ligands. Ethanedioate. Ethane-1,2-diamine.

Ligands which have more than 1 coordinate bond are called multidentate ligands. EDTA4- is an example of a multidentate ligand. It can form 6 coordinate bonds with the central metal ion.

The shape is dependent on the size of the ligands and the coordination number The coordination number is the number of coordinate bonds in a complex. IT IS NOT THE NUMBER OF LIGANDS

Some ligands are small and you can fit 6 of them around a central metal ion. H2O NH3 OH- Some ligands are larger and you can only fit 4 of them around the central metal ion - CL-. Ethanedioate and Ethane -1,2-diamine are larger still. Normally you have 3 of these around a central metal ion

They form octahedral shapes Example would be CO[(H2O)6]2+ or CO[(NH3)6]2+ All bond angles in an octahedral complex are 90 degrees

They form a tetrahedral shape and square planar shapes Examples are [CuCl4]2-. 109.5 degrees in this tetrahedral shape A specific example of square planar is the anti cancer drug cis - platen. Pt[(NH3)2(Cl)2]. Bond angles are always 90 degrees

Complexes have a charge which is the same as its total oxidation state. Total oxidation state = total oxidation state - total oxidation state of ligands

It is a multidentate ligand that is found in the molecule haemoglobin. It is a protein that is used to transport oxygen around the body in blood. The structure is octahedral. 4 of the nitrogens come from 1 multidentate ligand called haem. One of the coordinate bonds comes from a large protein called globein. The final coordinate bond comes from either an oxygen or water molecule Oxygen substitutes the water ligand where the oxygen concentration is high to form oxyhaemoglobin. This is transported around the body. Oxyhaemoglobin then gives up oxygen to a place where it is needed. Water takes the place and haemoglobin returns back to the lungs to start the process again

Carbon monoxide is a poisonous gas that causes headaches, unconsciousness and even death. It is known as the silent killer If co is inhaled the water ligand is replaced with a carbon monoxide ligand/ Unfortunately carbon monoxide bonds strongly so it’s not readily replaced y oxygen or water. This means that oxygen can’t be transported and leads to oxygen starvation in organs. Hence why carbon monoxide is poisonous

Complex ions show optical isomerism Complexes are optical isomers when they are non superimposable mirror images Octahedral complexes with 3 bidentate ligands show optical isomers like the ones shown to the left

Octahedral complexes with 4 ligands of the same type and 2 ligands of diff type display cis-trans isomerism. If the 2 different ligands are opposite each other you have a trans isomer. If the 2 diff ligands are adjacent to each other you have a cis isomer Square planar complexes with 2 ligands of the same type and 2 ligands of a different type display cis-trans isomerism. If the 2 ligands are opposite each other - you have a trans isomer but if the 2 ligands are adjacent we have a cis isomer.

The D subshell is split into 2 when ligands bond with the central metal ion. For example in terms of arrows, 22111 will split into 11 above and 221 below When electrons absorb light energy some move from the lowest energy level (ground state) to higher energy level orbitals (excited state) In order for this to happen, the energy from the light must equal the change in energy

The central metal ion and its oxidation state The type of ligand The coordination number

Some frequencies of visible light are absorbed by transition metal complexes. The frequencies absorbed depends on the size of the energy gap Frequency increases from one side at red to the other side of the visible spectrum at violet/purple. Frequencies which aren’t absorbed are reflected or transmitted [Cu(H2O)6]2+ absorbs frequencies that produce red light. The complementary colour is light blue (cyan) so we observe this colour. For those complexes where we have a full or empty 3d subshell no electrons can migrate to the higher energy level. This means we see these complexes as colourless or white.

White light is made of the colours we see above. When this hits a transition metal solution, only one frequency is absorbed. Any frequency which is not absorbed are reflected or transmitted. The combination of all these frequencies create a complementary colour that we observe. Essentially if we mix the complementary colour and the absorbed colour we get white light. The colour directly opposite the colour observed is what is absorbed. From top clockwise. Red Yellow Green Cyan Blue Magenta