DM - Inorganic chemistry and the periodic table *01

Question 1

where are transition metals found in the periodic table?

Answer 1

d-Block

Question 2

what is a transition metal?

Answer 2

a d-Block element that can form at least one stable ion with an incomplete d sub-shell

Question 3

why isn’t scandium a transition metal?

Answer 3

only forms one ion Sc3+

this has an empty d sub-shell

electronic config. [Ar]3d14s2 so when it loses 3 e- has electronic config. [Ar]

Question 4

why isn’t zinc a transition metal?

Answer 4

only forms one ion, Zn2+

this has a full d sub-shell

electron config. = [Ar]3d104s2

when it form Zn2+ it loses 2 e- (both form 4s sub-shell) so it keeps its full 3d sub-shell

Question 5

which sub-shell to transition metals lose electrons from 1st to form ions?

Answer 5

4s sub-shell

Question 6

transition metals - special chemical properties

Answer 6

1. variable oxidation states

2. form coloured ions in solution

Question 7

transition metals - iron properties

Answer 7

oxidation states =
+2 and +3

coloured precipitate =
Fe2+ - green
Fe3+ - orange

coloured aq =
Fe2+ - green
Fe3+ - yellow

Question 8

transition metals - copper properties

Answer 8

oxidation states =
+1 and +2

coloured precipitate =
Cu2+ - pale blue

colour in aq =
Cu2+ - blue

Question 9

what is a complex ion?

Answer 9

a complex (or complex ion) is a central metal atom or ion surrounded by coordinately bonded ligands

Question 10

what is a ligand?

Answer 10

an atom, ion or molecule that donates a pair of electrons to a central transition metal ion to form a coordinate (dative) bond.

Question 11

what is ligand substitution?

Answer 11

one ligand can be swapped for another - usually causes a colour change.

Question 12

how do ligands form bonds?

Answer 12

using lone pairs of electrons

they donate a pair of electrons to a central transition metal ion to form a coordinate (dative) bond

Question 13

what is a mono/unidentate ligand?

Answer 13

ligands with one lone pair of electrons

Question 14

what is a bidentate ligand?

Answer 14

ligands with two lone pairs of electrons

Question 15

what is a polydentate ligand?

Answer 15

ligands with more than two lone pairs of electrons

Question 16

ligand substitution reactions - what happens when ligands similar size?

Answer 16

the coordination number does change and neither does the shape

colour does change

eg. H2O, NH3 or CN-

for example
[Cr9(H2O)6]3+ + 6NH3 [Cr(NH3)6]3+ + 6H2O
octrahedral octrahedral
dark green purple

Question 17

ligand substitution reactions - what happens when ligands different sizes?

Answer 17

change in coordination number and shape and colour

eg. H2O and Cl-

for example:
[Cu9H2O)6]2+ + 4Cl- [CuCl4]2- + 6H2O
octrahedral pale blue —-> tetrahedral yellow

Question 18

ligands substitution reactions - why + what happens when substitution only partial?

Answer 18

happens when you add excess ammonia

for example:
[Cu(H2O)6]2+ + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O
octrahedreal in excess octrahedral
pale blue dark blue

Question 19

what happens to transitions metals when react with sodium hydroxide?

Answer 19

form brightly coloured precipitates

copper 2+ does this with - NH3 - too

Question 20

transition metal hydroxides + OH-: COPPER (II)

Answer 20

[Cu(H2O)6]2+ (aq) + 2OH- (aq) ——> [Cu(OH)2(H2O)4] (s) + 2H2O (l)
PALE BLUE percipitate
or
Cu2+ (aq) + 2OH- (aq) —-> Cu(OH)2 (s)

Question 21

transition metal hydroxides + NH3: COPPER (II)

Answer 21

[Cu(H2O)6]2+ (aq) + 2NH3 (aq) ——> [Cu(OH)2(H2O)4] (s) + 2NH4+ (aq)
PALE BLUE solution ——> BLUE precipitate

Question 22

transition metal hydroxides + NH3 (IN EXCESS!!) : COPPER (II)

Answer 22

1. [Cu(H2O)6]2+ (aq) + 2NH3 (aq) ——> [Cu(OH)2(H2O)4] (s) + 2NH4+ (aq)
   PALE BLUE solution BLUE percipitate
2. reacts further
   —> [Cu(NH3)4(H2O)4] (aq)
   DARK BLUE solution

Question 23

transition metal hydroxides + OH-: IRON (II)

Answer 23

[Fe(H2O)6]2+ (aq) + 2OH- (aq) ——> [Fe(OH)2(H2O)4] (s) + 2H2O (l)
PALE GREEN solution ——> DARK GREEN precipitate

when left standing
—-> green precipitate darkens

Question 24

transition metal hydroxides: what happens when [Fe(OH)2(H2O)4] (s) is left standing

Answer 24

green precipitate DARKENS

Question 25

transition metal hydroxides + NH3: IRON (II)

Answer 25

[Fe(H2O)6]2+ (aq) + 2NH3 (aq) ——> [Fe(OH)2(H2O)4] (s) + 2NH4+ (aq)
PALE GREEN solution DARK GREEN precipitate

when left standing
—-> green precipitate darkens

Question 26

transition metal hydroxides + OH-: IRON (III)

Answer 26

[Fe(H2O)6]3+ (aq) + 3OH- (aq) ——> [Fe(OH)3(H2O)3] (s) + 3H2O (l)
YELLOW solution —–> ORANGE precipitate

when left standing
—-> orange precipitate darkens

Question 27

transition metal hydroxides: what happens when [Fe(OH)3(H2O)3] (s) is left standing

Answer 27

orange precipitate DARKENS

Question 28

transition metal hydroxides + NH3: IRON (III)

Answer 28

[Fe(H2O)6]3+ (aq) + 3NH3 (aq) ——> [Fe(OH)3(H2O)3] (s) + 3NH4+ (aq)
YELLOW solution ——-> ORANGE precipitate

when left standing
—-> orange precipitate darkens

Question 29

can copper (II) hydroxide form complexes with ammonia (NH3)?

Answer 29

yes

Question 30

can iron (II) hydroxide form complexes with ammonia (NH3)?

Answer 30

no

Question 31

can iron (III) hydroxide form complexes with ammonia (NH3)?

Answer 31

no

Question 32

origin of colour in transition metals?

Answer 32

normally 3d orbitals of transition metals ions all have the same energy

when ligands bond to the ions they SPLIT the 3d orbitals, and some of the orbitals gain energy

this splits the 3d orbitals into two different energy levels

electrons tend to occupy the lower orbitals - to jump to higher orbitals they need the energy EQUAL to the ENERGY GAP
- they get this energy from visible light

Question 33

what is the amount of energy needed to make electrons jump to a higher orbital depend on?

Answer 33

the central ion

its oxidataion state

the coordination number

size of the energy gap

Question 34

what does the colour of compounds depend on?

Answer 34

the complement of those that are absorbed

when visible light hits a transition metal ion all the same energy, some frequencies are absorbed when electrons jump up to higher orbitals
the frequencies absorbed depend on the size of the energy gap

the rest of the frequencies are transmitted or reflected

• these frequencies combine to make the complement of the colour of the absorbed
• this is the colour you see

Question 35

origin of no colour - what if no 3d electrons or 3d sub-level is full?

Answer 35

no electrons will jump

so no energy absorbed

if no energy absorbed, the compound will look white or colourless

Question 36

transition metals - why do they make good catalysts?

Answer 36

because they can change oxidiation states by gaining or losing electrons within their d-orbitals

they can transfer electrons to speed up reactions

Question 37

transition metals - why are catalysts good?

Answer 37

good for industry and for environment

they allow reactions to happen faster and at lower temperatures and pressures reducing energy usage

Question 38

transition metal catalysts - why can they pose health risks? (examples)

Answer 38

their compounds are toxic

copper - can damage liver and kidneys

manganese - can cause psychiatric problems

Question 39

transition metal catalysts - why can they pose health risks? (examples)

Answer 39

their compounds are toxic

copper - can damage liver and kidneys

manganese - can cause psychiatric problems

Question 40

what type of catalyst are transition metals?

Answer 40

heterogeneos and homogeneous

Question 41

transition metal catalysts - why are they heterogeneous?

Answer 41

its in a different phase from the reactants

• good because they can use their s- and d- orbirals for bonding to the reactant molecules

Question 42

transition metal catalysts - heterogeneous mechanism (3 stages)

Answer 42

1. the reactant molecule are attracted to the surface of the catalyst and stick to it
   - ADSORPTION
2. the surface of the catalyst activates the molecules so they react more easily
   - interactions weaken the bonds in the molecule making it easier to break and reform as products
3. the product molecules leave the surface of the catalyst making way for fresh reactants to take their place
   - DESORPTION

Question 43

transition metal catalysts - what makes a good heterogeneous catalyst?

Answer 43

1. attract reactant molecule strongly enough so that they are held to the surface long enough to react
2. not attract the product molecules to strongly
   - otherwise the molecules wont deabsorb and will block the catalyst from fresh reactants

Question 44

heterogeneous transition metal catalyst - Iron example

Answer 44

iron catalyses the reaction of nitrogen and hydrogen to make ammonia
- HABER PROCESS

Question 45

heterogeneous transition metal catalyst - CuSO4 example

Answer 45

catalysed reaction of zinc with acids

Question 46

heterogeneous transition metal catalyst - MnO2 example

Answer 46

catalyses decomposition of hydrogen peroxide

Question 47

why do transition metals make good homogeneous catalysts?

Answer 47

because transition metals have variable oxidation states

in the same physical state as reactants (usually (aq))

Question 48

homogeneous transition metal catalysts - mechanism

Answer 48

work by combining with the reactants to form an intermediate species which then reacts to form the products

• and reform the catalyst

the activation energy needed to form the intermediate (and form products from the intermediate) is lower than that needed to make the products directly from the reactants