KA 3: transition metals

Question 1

What are d-block transition metals?

Answer 1

Metals with an incomplete d subshell in at least one of their ions

Question 2

what does the filling of d-orbitals follow?

what are the exceptions?

Answer 2

the aufbau principle

chromium and copper atoms

Question 3

what are these exceptions due to?

Answer 3

the special stability associated with the d subshell being half-filled or completely filled

Question 4

what happens when atoms from the first row of the transition elements form ions?

Answer 4

it is the 4s electrons that are lost first rather than the 3d electrons

Question 5

what can be used to determine whether oxidation or reduction has occurred?

Answer 5

changes in oxidation number of transition metal ions

Question 6

what can oxidation be defined as?

Answer 6

an increase in oxidation number

Question 7

What can reduction be defined as?

Answer 7

decrease in oxidation number

Question 8

what are compounds containing metal in high oxidation states usually classed as?

Answer 8

oxidising agents

Question 9

what are compounds containing metal in ow oxidation states usually classed as?

Answer 9

reducing agents

Question 10

an element is said to be in a particular oxidation state when…

Answer 10

…it has a specific oxidation number

Question 11

how can the oxidation number be determined?

Answer 11

-uncombined elements have an oxidation number of 0

-ions containing single atoms have an oxidation number that is the same as the charge on the ion

-in most of its compounds, oxygen has an oxidation number of −2

-in most of its compounds, hydrogen has an oxidation number of +1

-the sum of all the oxidation numbers of all the atoms in a neutral compound must add up to zero

-the sum of all the oxidation numbers of all the atoms in a polyatomic ion must be equal to the charge on the ion

Question 12

what can a transition metal have in its compounds?

Answer 12

different oxidation states

Question 13

Compounds of the same transition metal in different oxidation states may have…

Answer 13

different colours

Question 14

ligands may be…

Answer 14

negative ions or molecules with non-bonding pairs of electrons that they donate to the central metal atom ion, forming dative covalent bonds.

Question 15

What can ligands be classified as?

Answer 15

Monodentate, bidentate up to hexadentate

Question 16

what happens in the formation of a simple covalent bond?

Answer 16

each atom supplies one electron to the bond

Question 17

What is a dative covalent bond?

Answer 17

a covalent bond (a shared pair of electrons) in which both electrons come from the same atom

Question 18

how is a dative bond shown?

Answer 18

using an arrow

Question 19

what is it possible to do?

Answer 19

to deduce the ligand classification from a formula or structure of the ligand or complex

Question 20

What is the coordination number?

Answer 20

The total number of bonds from the ligands to the central transition metal

Question 21

what is a complex?

Answer 21

a transition metal surrounded by ligands

Question 22

How can names and formulae be written?

Answer 22

-ligands are listed first followed by the metal

-if there is more than one type of ligand use the usual prefixes of di,tri etc

-when listing ligands, do so alphabetically (the prefixes don’t count)

Question 23

what do the IUPAC rules cover?

Answer 23

-central metals that obey the rules

-copper (cuprate) and iron (ferrate)

-ligands, including water, ammonia, halogens, cyanide, hydroxide and oxalate

-roman numerals are shown for the oxidation state of the metal

Question 24

how do you make the formula?

Answer 24

-the complex is enclosed within square brackets

-the metal symbol is written first then the ligands in alphabetical order

-the atom bound to the transition metal should always be listed first where reasonable to do so

-the charge on the complex goes outside the brackets

Question 25

what happens if a complex is overall negative?

Answer 25

the metal name ends in "-ate"

Question 26

what happens to the name if the complex has a positive or neutral charge?

Answer 26

the name doesn't change

Question 27

what happens to the d-orbitals in a complex of transition metals?

Answer 27

they're no longer degenerate

Question 28

what is the splitting of the d-orbitals into higher and lower energies due to?

Answer 28

repulsion between the electrons in the approaching ligand and electrons in orbitals lying along the axes.

Question 29

what does the extent of the splitting depend on?

Answer 29

the ligands involed

Question 30

what are strong field ligands?

Answer 30

Ligands that cause a large difference in energy between subsets of d orbitals

Question 31

what are weak field ligands?

Answer 31

ligands that cause a small energy difference between subsets of d orbitals

Question 32

what is the spectrochemical series?

Answer 32

where ligands are placed in an order of their ability to split d orbitals

Question 33

the greater the splitting the greater...

Answer 33

...the energy difference between the two subsets of orbitals

Question 34

when is light absorbed? and what does this account for?

Answer 34

When electrons in a lower energy d orbital are promoted to a d orbital of higher energy the colour of many transition metal complexes

Question 35

if light of one colour (from the visible spec) is absorbed, what happens?

Answer 35

the complementary colour will be observed

Question 36

what can transition metals and their compounds act as?

Answer 36

catalysts

Question 37

what state are heterogeneous catalysts in?

Answer 37

a different state to the reactants

Question 38

what can heterogeneous catalysts be explained in terms of?

Answer 38

-formation of activated complexes -the adsorption of reactive molecules onto active sites

Question 39

what is thought to allow activated complexes to form? what does this provide?

Answer 39

The presence of unpaired d electrons or unfilled d orbitals reaction pathways with lower activation energies compared to the uncatalysed reaction

Question 40

where does the reaction occur?

Answer 40

on the surface of the catalyst

Question 41

what happens when the reaction occurs om the surface of the catalyst?

Answer 41

* partially filled d-orbitals can form weak temporary bonds * this allows new bonds to form between atoms on the surface * the products move away (lower activation energy pathway) and the active site on the metal can be reused

Question 42

what state are homogeneous catalysts in?

Answer 42

the same state as the reactants

Question 43

how can homogeneous catalysts be explained?

Answer 43

in terms of changing oxidation states with the formation of intermediate complexes.

Question 44

give an example of the variability of oxidation states

Answer 44

(rochelle salts experiment)