3.4 - The D-block/transition elements

Question 1

What is a transition element?

Answer 1

A transition element is a d-block element which forms one or more stable ions with incomplete d-orbitals

Question 2

Why are Sc and Zn not counted as transition metals?

Answer 2

They do not have incomplete d-orbitals and so are not considered transition metals

Question 3

How do you work out the maximum oxidation state for a transition metal?

Answer 3

The number of 4s electrons plus the number of unpaired 3d electrons

Question 4

What are orbitals?

Answer 4

Orbitals are interpretations of mathematical equations which determine the probability of finding an electron in a given space.

Question 5

Describe dxy, dz and dyz

Answer 5

Each have 4 lobes in the same plane as eachother, 90* apart, each lobe is inbetween the 2 axis on that plane

Question 6

Describe dx2-y2

Answer 6

Has the same shape as the previous 3 orbitals but the lobes lie directly on the x and y axis

Question 7

Describe dz2

Answer 7

2 lobes which lie on the z axis with a ring or doughnut around the middle

Question 8

How does the melting point of transition metals differ from calcium and why?

Answer 8

Transition metals have a higher melting point than calcium
- in calcium the 4s electrons are involved in the metallic bond which holds the structure together
- in scandium onwards 3d electrons are also involved in the metallic bond
- this creates metallic bonds which are stronger and hence results in a higher melting point

Question 9

What happens to densities as you move across the d-block?

Answer 9

AS you move across the d-block the atomic radius decreases due to the increasing nuclear charge pulling the outer electrons closer to the nucleaus (the additional electrons filling up the nucleus)
- the size is smaller but the density is greater across d-block
- transition metals are more dense than calcium

Question 10

What are ligands?

Answer 10

Ligands are bases with a lone pair of electrons that forms a dative bond to a central metal atom/ion (they are attracted to metal ions)

Question 11

What are complex ions?

Answer 11

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

Question 12

Why do metals seek out ligands?

Answer 12

The positive metal ion is stablised by the ligands and so an ion will make as many bonds with as many ligands as it able (up to 6)

Question 13

What is a coordination number?

Answer 13

The number of coordinate bonds being formed to the metal ion (most commonly 2,4,6)

Question 14

What is a octahedral complex?

Answer 14

Six bonds attached to a central atom creates an octahedral complex to minimise repulsion between the bonding pairs

Question 15

What is a tetrahedral complex?

Answer 15

If the ligand is especially large than there will not be room to fit 6 ligands (due to steric hinderance)

Question 16

What is a square planar complex\?

Answer 16

Platinum is an exception to complexes with a cordination number of 4 (which normally are tetrahedral). There are 90* between each of the dative bonds

Question 17

What is a linear complex?

Answer 17

Forms with 2 ligands, coord number of 2, an example is the active species in the tollens test for aldehydes

Question 18

What is a meant by a monodentate bond?

Answer 18

The ligand bonds to the metal ion with only 1 co-ordinate bond

Question 19

What is a chelate bond?

Answer 19

Bonds to the metal ion twice in 2 different locations, forming a ring

Question 20

Why are chelate bonds preffered?

Answer 20

They are very stable as they often replace multiple monodentate ligands, a reaction which has an increase in entropy.

Question 21

What is meant by bidentate?

Answer 21

Attached to the metal ion with 2 dative bonds per ligand

Question 22

What is meant by multidentate?

Answer 22

Attach to the central metal ion with 3 or more dative bonds

Question 23

What is EDTA?

Answer 23

Ethyldiammineteraacetic acid is a hexadentate ligand
- it can trap ions and in doing so reduces their reactivity
- it reduce metal ion impurities and chelation therapy can remove mercury and lead when somebody is poisoned

Question 24

What is a ligand exchange reaction?

Answer 24

When one or more ligands are taken from a complex and replaced

Question 25

What causes the characteristic colour of copper?

Answer 25

The characteristic blue colour (sulphate and chloride) is due to the presence of hexaaquacopper (II) ion

Question 26

What colour is anhydrous copper?

Answer 26

Anhydrous salts contain no water molecules, white anhydrous copper sulphate is added turns blue

Question 27

What happens when you add dilute ammonia to copper?

Answer 27

• ammonia solution acts as a base
  blue solution to pale blue precipitate

Question 28

What happens when you add ammonia to copper in excess?

Answer 28

Pale blue precipitate - deep blue solution

Question 29

What happens when you add HCl to copper?

Answer 29

Initiates the ligand exchange
Blue solution to a green solution

Question 30

What happens when you add sodium hydroxide to cobalt?

Answer 30

Pink solution to a blue precipitate

Question 31

What happens when you add ammonia to cobalt?

Answer 31

Pink solution to green precipitate

Question 32

What happens when you add excess ammonia to cobalt?

Answer 32

Green precipitate to brown solution

Question 33

What happens when you add HCl to cobalt?

Answer 33

Pink solution to a blue solution

Question 34

What will occur in transition redox reactions?

Answer 34

A change in colour

Question 35

What can fe2+ be oxidised with?

Answer 35

H+/MnO4-
Purple to pink

Question 36

What can fe2+ be reduced with?

Answer 36

I-
Turns dark blue (stronger with starch)

Question 37

What can Cr3+ be oxidised with?

Answer 37

h2o2 (OH-)
green to yellow

Question 38

What can Cr2O7 2+ be reduced with?

Answer 38

Zn/H+
orange to green

Question 39

What is Cu2+ reduced with?

Answer 39

I-
white to brown

Question 40

How can Cu2+ disproportionate?

Answer 40

Turns into cu2+ and cu
pink/brown solid to light blue

Question 41

Why are transition metal complexes different colours?

Answer 41

The origin of colour in transition metal complexes results from the absorption of light energy as the electrons moves between 2 non-degenerate orbitals

Question 42

What is octahedral splitting?

Answer 42

The energy levels of the d-orbitals are raised so they are no longer degenerate
- they are not raised by the same amount

Question 43

What is tetrahedral spliiting?

Answer 43

When 4 anions approach the ions and form a tetrahedral complex, more complex repulsions cause splitting of the orbitals into 2 distinct levels

Question 44

What does the energy gap between the high energy and low energy non-degenerate orbitals depend on?

Answer 44

• the metal ion
• the metals oxidation state
• the type of ligands surrounding the metal ion
• the arrangement of ligands surrounding the metal ion
• the number of ligand changes the coordination number but you will also be changing the ligands

Question 45

What is catalysis?

Answer 45

The increase in rate of reaction caused by the addition of a catalyst

Question 46

What is a homogeneous catalyst?

Answer 46

In the same phase as the reactant

Question 47

What is a heterogeneous catalyst?

Answer 47

Different phase as the reactant (eg the haber process)