compounds and complexes

Question 1

atomic radius of group 6 elements (Cr, Mo, W and Sg)

Answer 1

increases Cr to Mo

W and Mo are the same due to lanthanoid contraction (poor shielding of 4f)

Question 2

ionisation energy of g6

Answer 2

increases down due to increase in Zeff
subsequent removal of electrons from 2nd and 3rd row transition metals becomes easier due to shielding by inner electrons - gradual increase in 2nd and 3rd IE
end and 3rd row are more stable in high ox states and are easily oxidised

Question 3

chemistry of chromium

Answer 3

group state 4s1 5d5 (stable half filled)

common ox states are 2,3 (most stable) and 6

Question 4

oxoanions? for Cr?

Answer 4

negatively charged ions containing two or more elements (one is oxygen)
common for group 6
charged metal ions do not exist in isolation
oxoanion for Cr6+ is CrO42-

Question 5

Cr0 and Cr2+

Answer 5

strong reducing agents that oxidise to Cr3+

Question 6

Cr6+

Answer 6

is a strong oxidising agent in acids

Question 7

as ox state increases…

Answer 7

tendency to remove electrons decreases - more electronegative, less metallic and more acidic (more able to accept an electron from a donor compound)

Question 8

Cr2O3

Answer 8

amphiprotic (acid or base)

Question 9

Coordination complex

Answer 9

a central atom bonded to molecules or anions (called ligands)

• cations are Lewis acids (electron pair acceptors)
• ligands are Lewis bases (electron pair donors)
• bonds are called coordinate bonds, donor covalent bonds or dative bonds

Question 10

coordination compound

Answer 10

a salt (anion + cation) in which one or both ions is a coordination complex

• counter ions may be present to maintain charge or balance in the coordination compound
• compound may dissociate in solution and acts as an electrolyte
• ligands remain attached to the metal ion

Question 11

kepert theory

Answer 11

complex shapes depend on repulsion of ligands

Question 12

coordination number

Answer 12

the number of donor atoms around the metal

Question 13

donor atom

Answer 13

atom that forms the coordination bond around the metal

Question 14

linear

Answer 14

2 donors

Question 15

trigonal planar

Answer 15

three donors

Question 16

tetrahedral

Answer 16

4 donors (exception: some are square planar)

Question 17

trigonal bipyramidal

Answer 17

5 donors (aka square-based pyramidal)

Question 18

octahedral

Answer 18

6 donors

Question 19

components of coordination complexes

Answer 19

• always drawn in square brackets
• central atom
• ligands surrounding
• charge on the outside

Question 20

components of coordination compounds

Answer 20

• cation comes first
• no charge, it is implicit from counter ions
• counter ion
• square brackets
• might have a hydrate

Question 21

oxidation states

Answer 21

complex charge - sum of ligand charges