Transition Elements

Question 1

What are the types of d-orbitals in transition metals?

Answer 1

dxy,dxz, and dyz have d-orbitals in between axes; dx2-y2 and dz2 have d-orbitals along axes.
Dz2 is formed by the merging of dx2-z2 and dy2-z2

Question 2

What causes variable oxidation states in transition metals?

Answer 2

The small energy difference between 4s and 3d allows electrons from both subshells to be removed, forming various oxidation states.

Transition metals have partially filled d-orbitals, leading to variable oxidation states.

All transition metal exhibit two or more oxidation states

Question 3

What is the most common oxidation state of transition metals?

Answer 3

The most common oxidation state is +2 when 2 electrons from 4s are lost.

Question 4

When do transition elements exhibit their highest oxidation states?

Answer 4

Transition elements show the highest oxidation states when they combine with oxygen or fluorine as they are the most electronegative.

Question 5

What types of compounds do transition elements form in high oxidation states?

Answer 5

In high oxidation states above +4, they form large oxyanions and covalent compounds (acidic oxides) like CrO4 or MnO4.

Question 6

What types of compounds do transition elements form in lower oxidation states?

Answer 6

In lower oxidation states, they form ionic compounds (basic oxides).

Question 7

What is a complex in chemistry?

Answer 7

A complex is an ion or molecule formed by a central metal atom/ion surrounded by one or more ligands.

A complex consists of
a central transition metal ion (+ve) that can accept electrons and
Ligands (-ve) which is a species that contains a lone pairs of electrons that forms a dative bond to a central metal atom/ion.

Question 8

What are the components of a complex?

Answer 8

A complex consists of a central transition metal ion that can accept electrons and ligands that donate lone pairs of electrons.

Question 9

What is the coordination number in a complex?

Answer 9

The coordination number is the number of coordinate or dative bonds to the central metal atom/ion.
Different metal ions show different coordination number with same ligands.

Question 10

Why do transition metals form complexes?

Answer 10

Transition metals form complexes because:
Ions are small in size so they have a strong electric field around them which attracts electron-rich ligands.
They have empty 4s and 4p orbitals that are hybridised and can accept electrons.

Question 11

What are monodentate ligands?

Answer 11

Monodentate ligands form only one coordinate bond with the central metal ion, donating one pair of electrons.

Examples include halide ions (F-, Cl-, Br-, I-), sulfide (S2-), nitrite (NO2-), hydroxide (OH-), cyanide (CN-), and thiocyanate (SCN-).

Neutral ligands include water (H2O), ammonia (NH3), and carbonyl (CO).

Question 12

What are bidentate ligands?

Answer 12

Bidentate ligands form two coordinate bonds with the central metal ion, donating two pairs of electrons per molecule.

Ethylene diamine (en) is a neutral bidentate ligand that forms 6 coordinate bonds.

Oxalate ion (oxalato-)

Question 13

How do we write formulae of complexes

Answer 13

*Metal ion written first followed by ligand
*Place charge on formula in square br
*Total charge on complex= sum of charge on metal ions and charge on ligand
*If ligands all neutral, charge on complex= charge on metal ion

Question 14

Describe the shapes of complexes with their coordination number and shape

Answer 14

Coordination number is 6 and shape octahedral with bond angle 90

Coordination number is 4 and shape tetrahedral with bond angle 109.5

Coordination number is 4 and shape square planar and bond angle 90. This happens when the ligands consists of two or more atoms and usually the central atom is Ni and Pt)

Coordination number is 2 and shape linear and bond angle 180.

Question 15

What is cis-platin?

Answer 15

Cis-platin is an anticancer drug that acts by binding to DNA in cancer cells, preventing cell division. Trans-platin will not have the same beneficial medical effects.

Question 16

What are geometric isomers?

Answer 16

Molecules or ions with the same molecular formula and the same molecular formula and same bonds between their atoms but which cannot be superimposed on each other, due to some lack of rotation around their bonds.These are also known as cis/trans isomers.

Question 17

Describe the differences in electronegativity in geometrical isomerism

Answer 17

Cis isomers will have two identical groups on one side of any square planar complex. So any difference in electronegativity between the two pair of isomers will cause an imbalance of charge making a polar complex.

However, the trans isomer will have identical lies directly opposite each other at the corners of the square planer complex so the charge is balanced and results in a non-polar complex.

Question 18

What is stereoisomerism?

Answer 18

Two isomers that are mirror images of each other and cannot be super imposed. They are optical isomers. They differ only in their ability to rotate the plane or polarise light in opposite directions.

Stereoisomerism is commonly shown by octahedral complexes associated with bidentate ligands.

Question 19

What is the reaction of Cu2+ (aq) with hydroxide ions?

Answer 19

[Cu(H2O)6]2+(aq)+2OH-(aq) ➡️ Cu(OH)2(H2O)4(s) + 2H2O(l)

Blue solution turns to pale blue precipitate

Not ligand exchange, hydroxide ions remove hydrogen ions from water ligand?

Question 20

What is the reaction of CU2+ (aq) with ammonia solution?

Answer 20

Small amounts of ammonia
[Cu(H20)6]2+ +2NH3 ➡️ Cu(H2O)4(OH)2 + 2NH4+

blue solution turns into pale blue precipitate

Initially, ammonia act as a base and hydrogen ions are pulled off the hexaaqua ions as above

Excess ammonia:

Cu(H2O)4(OH)2 + 4NH3 ➡️ [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-

Pale blue pot turns into deep blue solution

Ammonia replaces water as ligand
Only 4 of 6 water molecules replaced

Question 21

What is the reaction of CU2+ (aq) with chloride ions?

Answer 21

If we add hydrochloric acid drop by drop

[Cu(H2O)6]2+(aq) + 4Cl- (aq) 🔄 [CuCL4]2- (aq) + 6H2O (l)

Blue solution changes to yellow solution

The mixture of blue and yellow solution in the reaction mixture gives a greenish colour.

Question 22

What is the reaction of Co2+ (aq) with hydroxide ions?

Answer 22

[Co(H2O)6]2+ (aq) + 2OH- (aq) ➡️ Co(OH)2(H2O)4(s) +2H2O (l)

Pink solution turns to blue precipitate

Blue precipitate turns red when warmed if the alkali is in excess

Question 23

What is the reaction between Co2+ (aq) and concentrated aqueous ammonia drop by drop?

Answer 23

[Co(H2O)6]2+(aq) + 6NH3 (aq) ➡️ [Co(NH3)6]2+ (aq) + 6H2O (l)

Pink solution turns into brown solution

Question 24

What is the reaction between Co2+(aq) and concentrated hydrochloric acid drop by drop?

Answer 24

[Co(H2O)6]2+(aq) + 4Cl- (aq) ➡️ [CoCl4]2- (aq) + 6H2O (l)

Pink solution to blue solution