Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A Level Chemistry > Module 5 (chapter 24) - transition elements > Flashcards

Module 5 (chapter 24) - transition elements Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

background information about d-block elements

A
  • are all metallic, displaying the typical physical properties of metals
  • they have high melting and boiling points, shiny in appearance and conduct electricity and heat
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

uses of transition metals

A
  • copper, silver, nickel and zinc have been used in coinage for many years
  • iron is used in construction and the production of tools
  • copper is used for electrical cables snd water pipes
  • titanium is known for its great strength and use in aerospace and joint replacement
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

electron configuration of d-block elements

A

-the electron configuration of an atom or iron shows the arrangement of electrons in shells and sub shells
-electron occupy orbitals in order of increasing energy
-the electron configuration of chromium and copper don’t follow the expected principle for placing electron singly in orbitals before pairing
-this is due to stability
-a half filled d5 sub-shell and a fully filled d10 sub shell give additional stability to atoms
chromium (1s2,2s2,2p6,3s2,3p6,3d5,4s1)
copper (1s2,2s2,2p6,3s2,3p6,3d10,4s1)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

rules when gaining and losing electrons

A
  • when forming an atom, the 4s orbital fills before the 3d orbital
  • when forming an ion, the 4s orbital empties before the 3d orbital
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

transition elements

A

they are d-block elements that form at least one ion with a partially filled d-orbital
-you can be a d-block element but not a transition element

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

why is scandium not a transition element?

A

scandium only forms Sc3+ ions by loss of two 4s electrons and one 3d electron

  • it only has one electron in the 3d orbital and therefore its electron configuration becomes 1s2,2s2,2p6,3s2,3p6
  • does not have a partially filled d orbital and so isn’t a transition element
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

why is zinc not a transition element?

A
  • zinc only forms the Zn2+ ion by the loss of two 4s electrons
  • the electron configuration of Zinc means that when these two electrons are lost it still has a full 3d shell snd so it is not half full.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

properties of transition metals

A
  • they form compounds in which the transition element has different oxidation states
  • they form coloured compounds
  • the elements and their compounds can act as catalysts
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

variable oxidation states

A
  • transition elements form compounds with more than one oxidation state.
  • iron forms two chlorides for example (iron(II) chloride and iron(III) chloride
  • the number of oxidation states increases across the transition elements series to manganese, and then decreases.
  • all of the transition elements form compounds with an oxidation number of +2, resulting from the loss of two electrons
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

formation of coloured compounds

A
  • compound and ions of transition elements are frequently coloured
  • potassium dichromate is bright orange
  • cobalt (II)chloride is pink/purple
  • nickel sulphate is green
  • hydrated copper sulfate is blue
  • the colour of a solution is linked the partially filled d-orbitals of the transition metal ion. the colour can vary with different oxidation states (e.g. iron)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

catalysts

A
  • iron is used to catalyse the hater process which manufactures ammonia
  • vanadium oxide is used to catalyse the contact process and the production of surfer trioxide from surfer dioxide
  • nickel is used yo catalyse the hydrogenation of vegetable fats when making margarine
  • manganese oxide is used to catalyse the decomposition of hydrogen peroxide to form oxygen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what type of catalysts are the named transition metals

A
  • heterogeneous catalysts
  • some are homogeneous
  • e.g. reaction between iodide ions and peroxodisulfate ions is catalysed by Fe2+ ions, with reactants and catalyst all in aqueous solution
  • when the reaction is carried out with a trace of starch, a blue-black colour forms showing the formation of iodine. when catalyst added this precipitate forms much quicker
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

complex ions

A

d-block elements form complex ions

-other elements like aluminium can also form complex ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

how do complex ions form?

A
  • when one of more molecules of negatively charged ions bond to a central metal ion. these molecules or ions are known as ligands
  • the coordination number indicates the number of coordinate bonds attached to the central metal ion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

ligand

A

a molecule of ion that donates a paid of electrons to a central metal ion to form a coordinate bond or date covalent bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

how are complex ions represented

A
  • complex ion is enclosed inside square brackets with the overall change of the complex shown outside the square brackets
  • the overall charge is the sum of the charges on the central metal ion and any ligand present.
17
Q

monodentate ligands

A 
-a ligand that is able to donate one pair of electrons to a central metal ion 
water (neutral)
ammonia (neutral)
chloride (-1)
cyanide (-1) 
hydroxide (-1)
18
Q

bidentate ligands

A
  • ligands that can donate two lone pairs of electrons to the central metal ion, forming two coordinate bonds
  • the most common are:
  • 1,2 -diaminoethane (each nitrogen atom donates a paid of electrons to the central metal ion forming a coordinate bond)
  • ethandioate (each negatively charged oxygen atom donates a lone pair of electrons to the central metal ion)
19
Q

shapes of complex ions

A
  • depends upon its coordination number. the commonest coordination numbers six and four
  • many complex ions have a coordination number of six, given an octahedral shape (bond angles of 90 degrees)
20
Q

four coordinate complexes

A
  • tetrahedral complexes are the most common with bond angles of 109.5 degrees around the central metal ion (e.g. CoCl4 and CuCl4) both 2-
  • square planar complexes occur in complex ions of transition metals with eight d electrons in the highest energy d sub shell (platinum, palladium and gold)
  • Im this structure, ligands are arranged at the corners of a square
21
Q

stereoisomers

A

complex ions can display two types of steriosiomerism

  • cis/trans isomerism
  • optical isomerism
  • the type of stereoisomerism depends on the number and type of ligands that are attached to the central atom plus the shape of the complex
  • some four coordinate and six coordinate complex ions containing two different types of monodentate ligands show cis-trans isomerism
  • some six coordinate complex ions containing monodentate and bidentate ligands can show both cis/trans and optical isomerism
22
Q

cis/trans isomerism in complex ions

A
  • no C=C double bond is required and the shape of the complex holds groups in different orientations about the central metal ion
  • occurs in square planar and octahedral complexes
23
Q

cis-trans isomerism in quake planar complexes

A
  • ligands are arranged in the same planes with 90 degree bond angles
  • in the cis-isomer, the two identical groups are adjacent to each other, whereas in the trans isomer the two identical groups are opposite each other
  • in the cis isomer the coordinate bonds between the identical ligands are 90 degrees apart vs 180 degrees in the trans-isomer
24
Q

cis-trans isomerism in octahedral complexes

A
  • complexes containing four of one type of ligand and two as another can show this. the cis isomer have identical glands adjacent to each other, the trans at 180 degrees
  • octahedral complexes containing bidentate ligands can also shoe cis-trans isomerism
  • if the other two atoms (not bidentate) are nest to each other is it cis, if they are opposite it is trans
25
Q

optical isomerism

A
  • can only occur in octahedral complexes containing two or more bidentate ligands
  • optical isomers called enantiomers are non-superimposable mirror images of each other
  • trans isomers cannot form optical isomers as a mirror image is exactly the same and cannot be superimposed
  • can also be seen in complexes containing three bidentate ligands
26
Q

ligand substitution

A
  • a reaction where one ligand in a complex ion is replaced by another ligand
  • e.g. when copper (II) sulphate is dissolved in water, the pale blue complex ion is formed in aqueous solution
27
Q

ligand substitution with ammonia

A
  • when an excess of (aq) ammonia is added to a solution containing [Cu(H2O)6]2+ the pale blue solution changes colour to form a dark blue solution
  • four ammonia ligands have replaced four water ligands
  • add ammonia drop wise so that all observations are seen (two reactions take place)
  • a pale blue precipitate of Cu(OH)2 is formed in the first stage of the reaction
  • the Cu(OH)2 precipitate then dissolves in excess ammonia to form a dark blue solution
28
Q

ligand substitution with chloride ions

A
  • concentrated HCl is used as a source of chloride ions
  • when an excess of concentrated hydrochloric acid is added to a solution containing [Cu(H20)6]2+, the pale blue solution changes colour to form a yellow solution [CuCl4]2-
  • six water ligands have been replaced by four chloride ligands
  • if water is added to the yellow solution, a blue solution will be formed, although more dilute and paler in colour than the original blue solution
  • an intermediate green solution is formed. this isn’t a new species but is the result of the yellow solution mixing with the blue solution to give a green colour as the reaction proceeds
  • the oxidation state of copper remains as +2. chloride ligands are large in size than water ligands, so fewer can fit around the central Cu2+ ion. this explains the change in coordination number
29
Q

reactions of aqueous chromium ions (chromium sulphate)

A
  • when chromium (III) potassium sulphate is dissolved in water, the complex ion [Cr(H2O)6]3+ is formed (purple solution)
  • when chromium sulphate is dissolved in water, a green solution containing chromium is formed [Cr(H2O)5 SO4]+ where one of the water ligands has been replaced by the sulphate ion
  • both solutions contain chromium (III) ions in oxidation state 3+
30
Q

reaction with ammonia

A
  • [Cr(H2O)6]3+ takes part in a ligand substitution reaction with an excess of (aq) ammonia forming [Cr(NH3)6]3+
  • when the ammonia is added drop-wise to the chromium(III) solution two steps take place
  • grey green precipitate forms of Cr(OH)3
  • the Cr(OH)3 precipitate dissolves in excess ammonia to form the complex ion [Cr(NH3)6]3+
  • all six ligands are substituted
31
Q

ligand substitution and haemoglobin

A
  • blood caries oxygen around the body due to the presence of haemoglobin (contains four proteins held together by weak intermolecular forces)
  • the central metal ion is Fe2+ which can bind to oxygen gas (O2)
  • blood passes through the lungs and the increased oxygen pressure allows haemoglobin to bind to it
  • it then binds to carbon dioxide after oxygen is released and carries this back to the lungs
  • carbon monoxide can also bind to the Fe2+. if carbon monoxide is breathed in a ligand substitution reaction takes place where the oxygen in haemoglobin is replaced by carbon monoxide
  • it bonds more strongly preventing a large proportion of the molecules form carrying oxygen (it is so strong the bond is irreversible)
32
Q

precipitation reactions

A

-occurs when two aqueous solution containing ions react together to form an insoluble ionic solid called a precipitate
-transition elements react with aqueous sodium hydroxide and aqueous ammonia to form precipitates
Cu2+, Fe2+, Fe3+ and Mn2+ all form precipitates on reaction with excess sodium hydroxide, none dissolve in excess

33
Q

oxidation of iron(II) to iron(III)

A

-acid conditions
-Fe2+ is oxidised to Fe3+
-MnO4- is reduced to Mn2+
-the solution containing MnO4- ions is purple and is decolourised by Fe2+ ions to form a colourless solution containing Mn2+ ions
MnO4- + 8H- + 5Fe2+ –> Mn2+ + 5Fe3+ +4H2O

34
Q

reduction of Fe3+ to Fe2+

A

-when reacted with iodide ions, I-, the orange-brown Fe3+ ion are reduced to pale green Fe2+ ions
-colour change is obscured by the oxidation of iodide ions to form iodine which is a brown colour
2Fe3+ + 2I- –> 2Fe2+ + I2
-iodide ions are oxidised
-Fe3+ ions are reduced

35
Q

electrode potentials in redox reactions

A

-the more positive the electrode potential value, the equilibrium is more likely to gain electrons shift to the right and undergo reduction

36
Q

reactions of dichromate and chromium

A

-aqueous dichromate ions have an orange colour and aqueous chromium ions have a green colour
-acidified dichromate ions can turn can be reduced to chromium 3+ ions by the addition of Zinc
Cr2O7 (2-) +14H+ +3Zn –> 2Cr3+ +7H2O +3Zn2+
-with an excess of zinc, chromium ions are reduced further to chromium (2+) which is pale blue
Zn + 2Cr3+ –> Zn2+ + 2Cr2+

37
Q

oxidation of chromium ions to CrO4 (2-)

A

-hot alkaline hydrogen peroxide (H2O2) is a powerful oxidising agent
3H2O2 + 2Cr3+ + 10OH- –> 2CrO4- + 8H2O
-chromium oxidised from 3+ to +6
-oxygen reduced from -1 to -2

38
Q

reduction of copper (II) to copper (I)

A

when aqueous copper reacts with excess iodine ions:
-I- is oxidised to brown iodine (I2)
-Cu2+ is reduced to Cu+
-this forms a white precipitate of copper iodide
2Cu2+ +4I- –> 2CuI + I2

39
Q

disproportionation of Cu+ ions

A
  • when solid copper (I) oxide Cu2O reacts with hot dilute sulphuric acid, a brown precipitate of copper is formed together with a blue solution of copper sulphate
  • Cu+ ions have been oxidised and reduced
  • reduction (goes from +1 to 0 in Cu)
  • oxidation (goes from +1 to +2 in CuSO4)

A Level Chemistry (21 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions