DM 4 - Inorganic Chemistry and the Periodic Table

Question 1

What are transition metals?

Answer 1

Transition metals are d-block elements that can form one or more stable ions which have an incomplete d-subshell

Question 2

Where are the electronic configurations of chromium and copper?

Answer 2

The electron configurations of chromium and copper are exceptions to the rule of filling up subshells:
Chromium: 1s2 2s2 2p6 3s2 3p6 3d5 4s1
Copper: 1s2 2s2 2p6 3s2 3p6 3d10 4s1

Question 3

What are the common oxidation states of copper and iron?

Answer 3

• Copper normally has an oxidation state of one (Cu+) or two (Cu 2+)
• Iron normally has an oxidation state of two (Fe 2+) or three (Fe 3+)

Question 4

What are the colours of these ions (if any)?
Cu+, Cu 2+, Fe 2+, Fe 3+

Answer 4

Cu +: colourless
Cu 2+: blue
Fe 2+: green
Fe 3+: yellow/brown

Question 5

Why do transition metals have variable oxidation states?

Answer 5

The d subshell has a lot of stable states so different numbers of electrons can be lost to produce ions that are all stable

Question 6

What is a ligand?

Answer 6

A ligand is an electron donor that forms a dative covalent/coordinate bond with a central metal ion/atom

Question 7

What is a complex ion?

Answer 7

A central metal ion bonded via coordinate bonds to electron donors (ligands) that are either negatively charges or possess a lone pair of electrons

Question 8

What is a monodentate, bidentate and polydentate ligand?

Answer 8

Monodentate: Ligand forms 1 coordinate bond to the central metal ion, donating 1 electron pair
Bidentate: Ligand forms 2 coordinate bonds to the central metal ion, donating 2 electron pairs
Polydentate: Ligand forms many coordinate bonds to the central metal ion, donating many electron pairs

Question 9

What is a ligand substitution?

Answer 9

A ligand substitution reaction is where one ligand in a complex ion is replaced by another ligand

Question 10

What is a precipitation reaction?

Answer 10

When two ionic aqueous solutions react together to form an insoluble ionic solid, this is known as a precipitate

Question 11

How does iron(II) and iron(III) react with NaOH in a precipitation reaction?

Answer 11

Fe 2+(aq) + 2OH-(aq) –> Fe(OH)2(s)
green solution green precipitate
Fe 3+(aq) + 3OH-(aq) –> Fe(OH)3(s)
yellow solution orange/brown precipitate

Question 12

How does copper(II) react with NaOH in a precipitation reaction?

Answer 12

Cu 2+(aq) + 2OH-(aq) –> Cu(OH)2(s)
blue solution blue precipitate

Question 13

Why do transition metals make good homogeneous catalysts?

Answer 13

• Since transition metals have various oxidation states, they make good homogeneous catalysts
• This is because they are able to oxidise and reduce reactants and intermediates to form the desired product(s)

Question 14

Why do transition metals make good heterogeneous catalysts?

Answer 14

Using the 3d and 4s electrons of the atoms on the catalyst surface, transition metals can form weak bonds with reactants which make them more reactive

Question 15

Why are transition metal complexes often coloured?

Answer 15

• When light is incident on an object, some is absorbed
• It will only be absorbed if its energy equals the difference in energies between two energy levels of the atom
• If it does, an electron becomes excited and is raised to a higher energy level
• The difference in energy between the two energy levels is often equivalent to the wavelengths/frequencies of the visible region of the electromagnetic spectrum
• Therefore transition metal complexes often appear coloured