Transition Elements Flashcards
Define a d-block element
Located between groups 2 and 3/13 of the periodic table with their highest energy electrons in 3d orbital
What are the typical physical poperties of d-block elements
- All metallic
- High melting/boiling points
- Shiny in appearance
- Conduct electricity and heat
What is the electron configuration of vanadium, cobalt, copper and chromium
Vn- 1s2 2s2 2p6 3s2 3p6 3d3 4s2
Cr-1s2 2s2 2p6 3s2 3p6 3d5 4s1
Co- 1s2 2s2 2p6 3s2 3p6 3d7 4s2
Cu- 1s2 2s2 2p6 3s2 3p6 3d10 4s1
Why do chromium and copper not follow the expected pattern of electron configuration
It is believed that a half-filled d5 sub-shell and a fully filled d10 sub-shell give additional stability to atoms of chromium and copper
What happens when forming d-block ions
- When forming an atom, the 4s orbital fills before the 3d orbitals
- When forming an ion, the 4s orbital empties before the 3d orbital
Give the electron configuration of Fe and Fe2+
Fe- 1s2 2s2 2p6 3s2 3p6 3d6 4s2
Fe2+ -1s2 2s2 2p6 3s2 3p6 3d6
Define a transition element
- A d-block element that forms at least one stable ion with an incomplete d sub-shell
Name two d-block elements that aren’t transition elements at explain why
- Scandium and zinc
- Scandium only forms the Sc 3+ ion which has the electron configuration: 1s2 2s2 2p6 3s2 3p6 , so it doesn’t have an incomplete d-subshell
- Zinc only forms the Zn2+ ion which has the electron configuration 1s2 2s2 2p6 3s2 3p6 3d10, so it doesn’t have an incomplete d sub-shell
What are the three main properties of transition elements and give two examples of each
- They form compounds in which the transition element has different oxidation states
e. g. Iron can be Fe2+ or Fe3+ and manganese can be found as Mn2+ or as MnO4- - They form coloured compounds
e. g. solutions of Fe2+ are pale green, solutions of Fe3+ are pale yellow. And solutions of Mn2+ are pale pink but solutions of MnO4- are deep purple - The elements and their compounds can act as catalysts
e. g. Iron in Haber process and MnO2 can catalyse decomposition of H2O2
Define homogenous catalyst
A substance that increase the rate of a chemical reaction without being used up in the process, which is in the same state as the reactants it is acting on.
Define heterogenous catalyst
A substance that increase the rate of a chemical reaction without being used up in the process, which is in a different state to the reactants it is acting on.
List 5 processes where a transition metal catalyst is used
- Haber process
- Contact process
- Hydrogenation of vegetable oil
- Decomposition of hydrogen peroxide
- Reaction between iodate and peroxidisulfate ions
Name the catalyst used, the equation of the reaction and whether it is a heterogenous or homogenous catalyst for the Haber process
- N2(g) + 3H2(g) ↔ 2NH3(g)
- Iron catalyst
- Heterogenous
Name the catalyst used, the equation of the reaction and whether it is a heterogenous or homogenous catalyst for the Contact process
- 2SO2 (g) + O2 (g) ↔2SO3 (g)
- Vanadium (v) oxide, V2O5 (s)
- Heterogenous
Name the catalyst used, the equation of the reaction and whether it is a heterogenous or homogenous catalyst for the Hydrogenation of vegetable oil
- HC=CH+ H2 → -CH2-CH2-
- Nickel catalyst
- Heterogenous
Name the catalyst used, the equation of the reaction and whether it is a heterogenous or homogenous catalyst for the Decomposition of hydrogen peroxide
- 2H2O2 (aq) → 2H2O (l) + O2 (g)
- MnO2 (s), Manganese (IV) Oxide
- Heterogenous
Name the catalyst used, the equation of the reaction and whether it is a heterogenous or homogenous catalyst for the reaction between iodate and peroxidisulfate ions
- S2O8- (aq) + 2I- (aq) → 2SO4 2- (aq) + I2 (aq)
- Fe2+ (aq) ions
- Homogenous
- S2O8- + Fe2+ → 2SO4 2- + Fe3+
Fe3+ + 2I- → I2 + Fe 2+
Define complex ion
A transition metal ion bonded to ligands by coordinate bond (dative covalent bond)
Define coordinate bond
A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only; also known as a dative covalent bond
Define ligand
A molecule or ion that can donate a pair of electrons to the transition metal ion
How are complex ions formed
When one or more molecules or negatively charged ions bond to a central metal ion- these molecules are ligands
It forms co-ordinate bonds
How do you represent the formula of complex ions
- The complex ion is enclosed inside square brackets with the overall charge of the complex shown outside the square brackets
- An example is [Cr(H2O)6]3+ formed when CrCl3.6H2O is dissolved in water.
- Cr3+ is the central metal ion
- Water acts as a ligand with each water molecule donating a lone pair of electrons from the oxygen atom to the central metal ion to form a co-ordinate bond
- The co-ordination number is 6 as there are 6 co-ordinate bonds to the central metal ion
Define co-ordination number
The total number of coordinate bonds formed between a central metal ion and ligands
What is a monodentate ligand
- A ligand that is able to donate one pair of electrons to a central metal ion
List 5 examples of monodentate ligands and their charge
- Water, H2O, neutral
- Ammonia, NH3, neutral
- Chloride, Cl-, -1
- Cyanide, CN, -1
- Hydroxide, OH-, -1
What is a bidentate ligand
Ligands that can donate two lone pairs of electrons to the central metal ion, forming 2 coordinate bonds
List the 2 most common bidentate ligands
- 1,2-diaminoethane (en) NH2CH2CH2NH2, the Ns has the lone pairs of electrons
- Ethanedioate COOCOO, the single bond O has the lone pair of electrons
Show the formula, oxidation number and coordination number of the complex formed with en and Cobalt
- [Co(NH2CH2CH2NH2)3]3+
- Oxidation number of Co is +3
- The coordination number is 6 because there are three 1,2-diaminoethane ligands and each ligand forms two coordinate bond
What is the shape and bond angle of 6 coordinate bonds are formed
- Octahedral
- 90 degrees
- Look at shape p407
What are the two different shapes formed with complexes with a coordination number of 4
- Tetrahedral
2. Square planar
Describe the shape, bond angle and give two examples of tetrahedral complex ions
- 109.5 degrees
- [CoCl4]2- and [CuCl4]2-
- Normal tetrahedral shape
Describe when square planar shapes occur, the bond angle and the shape
- Square planar shape occurs in complex ions of transition metals with 8 d-electrons in the highest d-sub-shell.
- Platinum (II), palladium (II) and gold (III) fall in this category and tend to form square planar complexes
- Similar shape to octahedral but without ligands above and below the plane
- Bond angle- 90 degrees
Define stereoisomers
Compounds with the same structural formula but with a different arrangement of the atoms in space
What are the two types of stereoisomerism complex ions can display
- Cis-trans
2. Optical
When does cis-trans isomerism arise in complex ions
- Square planar complexes which contain no more than two identical ligands
- Octahedral complexes containing four of one type of ligand and two of another
- Octahedral complexes containing two bidentate and two of another
Which is the cis isomer and which is the trans isome
- In the cis-isomer the two ligands are adjacent
2. In the trans-isomer the two ligands are opposite ends
When does optical isomerism occur
- Octahedral complexes containing 3 bidentate ligands for optical isomers or enantiomers
- Octahedral complexes containing 2 bidentate and two monodentate ligands form optical and cis/trans
Name a complex ion isomer that is used in medicine
- Cis-platin
[Pt(NH3)2Cl2] - Square planar
- Neutral charge
What are the uses of cis-platin in medicine
- Clinical tests have proven that cis-platin attacks tumours and in many cases the tumours were seen to shrink in size
- It works by forming a platinum complex inside of a cell which binds to DNA and prevents the DNA of the cell from replicating
- Activation of the cell’s own repair system leads to apoptosis
What are the problems with using cis-platin
- It is quite toxic and has unpleasant side effects e.g. nausea and hearing loss
- Also can lead to kidney damage
Define ligand substitution
A reaction in which one or more ligands in a complex ion are replaced by different ligands
What happens when copper (II) sulfate is dissolved in water
- The pale blue complex ion [Cu(H2O)6]2+ is formed in aqueous solution
What happens when excess aqueous ammonia is added to a solution containing [Cu(H2O)6]2+
- [Cu(H2O)6]2+ (aq) + 4HN3 (aq) → [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O (l)
- Pale blue solution→Dark blue solution
- In the reaction 4 ammonia ligands have replaced four of the water ligands
- When adding the ammonia drop-wise you should see two different reactions taking place:
- A pale blue precipitate of Cu(OH)2 is formed in the first stage
- The Cu(OH)2 precipitate then dissolved in excess ammonia to form a dark blue solution
What happens when you mix chloride ions with [Cu(H2O)6]2+
- Concentrated HCl can be used as a source of chloride ions.
- When excess HCl is added, pale blue→yellow solution. 6 water ligands are replaced with 4 chloride ligands
- If water is added to the yellow solution→blue solution forms, but is more dilute and paler than the original blue solution.
- Intermediate green solution is formed as yellow+blue=green
- [Cu(H2O)6]2+(aq) + 4Cl-(aq) ↔ [CuCl4]2- (aq) + 6H2O (l)
- Change in coordination number as chloride ligands are larger than water ligands so fewer can fit around the central Cu2+
What forms when Chromium (II) potassium sulfate KCr(SO4)2.12H2O is dissolved in water
- The complex [Cr(H2O)6)]3+ forms
2. This is a pale purple solution
What forms when Chromium (III) sulfate is dissolved in water
- [Cr(H2O)5SO4]+
- Green solution
- One of the water ligands has been replaced by the sulfate SO4 2-
What happens when you mix [Cr(H2O)6)]3+ with excess ammonia
- It forms the complex ion [Cr(NH3)6]3+
- When the ammonia is added dropwise the reaction happens in two steps
- Initially grey-green precipitate of Cr(OH)3 is formed
- The Cr(OH)3 precipitate dissolves in excess ammonia to form complex ion [Cr(NH3)6]3+ - [Cr(H2O)6)]3+ (aq) + 6NH3 (aq) → [Cr(NH3)6]3+ (aq) + 6H2O (l)
- Violet→purple
Describe the the bonding of haemoglobin to oxygen, carbon dioxide and carbon monoxide
- Haemoglobin contains 4 protein chains held togeter by weak intermolecular bonds
- Each protein chain has a haem molecule within its structure
- The central metal ion in a haem group is Fe2+ which can bind to O2
- As blood passes through the lungs haemoglobin bonds to oxygen forming oxyhaemoglobin. This releases the oxygen to the body cells when required
- Haemoglobin can also bond to carbon dioxide, which is carried back to the lungs where it is released and exhaled
- Carbon monoxide can also bind to the Fe2+ ion in haemoglobin forming carboxyhaemoglobin.
- If carbon monoxide is breathed in a ligand substitution reactions takes place where the oxygen in haemoglobin is replaced y carbon monoxide
- Carbon monoxide binds to haemoglobin more strongly than oxygen, so a small proportion can prevent a large proportion of haemoglobin from carrying oxygen
- The bond is so strong it is irreversible so concentration of carboxyhaemoglobin becomes too high, oxygen transport is prevented leading to death
Define precipitation reaction
The formation of a solid from a solution during a chemical reaction. Precipitates are often formed when two aqueous solutions are mixed together.
What do transition metal ions react with to create a precipitate
NaOH (aq) and NH3 (aq)
But some of these precipitate will dissolve in excess of NaOH or NH3 to form complex ions in solution
State the observations and chemical equation for the reactions between Cu2+ ions and NaOH (aq)
- Blue solution reacts to form a blue precipitate of copper (II) hydroxide.
- The solution is insoluble in excess sodium hydroxide
- Cu2+(aq) + 2OH- (aq) → Cu(OH)2 (s)
State the observations and chemical equation for the reactions between Fe2+ ions and NaOH (aq)
- Pale green solution reacts to form green precipitate of iron (II) hydroxide
- The precipitate is insoluble in excess sodium hydroxide but turns brown at its surface on standing in air as iron (II) is oxidised to iron (III)
- Fe2+(aq) + 2OH- (aq) → Fe(OH)2 (s)
- Fe(OH)2 (s) → Fe(OH)3 (s) in air
State the observations and chemical equation for the reactions between Fe3+ ions and NaOH (aq)
- Pale yellow solution reacts to form an orange-brown precipitate of iron (III) hydroxide
- The precipitate is insoluble in excess sodium hydroxide
- Fe3+(aq) + 3OH- (aq) → Fe(OH)3 (s)
State the observations and chemical equation for the reactions between Mn2+ ions and NaOH (aq)
- Pale pink solution reacts to form light brown precipitate of manganese (II) hydroxide which darkens on standing in air
- The precipitate is insoluble in excess sodium hydroxide
- Mn2+(aq) + 2OH- (aq) → Mn(OH)2 (s)
State the observations and chemical equation for the reactions between Cr3+ ions and NaOH (aq)
- Violet solution reacts to form a grey-green precipitate of chromium (III) hydroxide
- The precipitate is soluble in excess sodium hydroxide forming a dark green solution
- Cr3+(aq) + 3OH- (aq) → Cr(OH)3 (s)
- Cr(OH)3 (s) + 3OH- (aq) →[Cr(OH)6]3- (aq)
What happens when only a few drops of ammonia is added to a transition metal ion
- If dilute or only a few drops the main ligand is OH-
2. NH3 + H2O↔NH4+ + OH-
What is the general equation for the reaction of concentrated/excess ammonia with a transition metal ion
- [m(H2O)6]n+ + 6NH3 ↔ [M(NH3)6]n+ + 6H2O
- Except Cu2+
[Cu(H2O)6]2+ + 4NH3 ↔ [Cu(NH3)4(H2O)2]2+ + 4H2O
State the observations and chemical equation for the reactions between Cu2+ ions and NH3 (aq)
- Cu2+ (aq) + 2OH- (aq) → Cu(OH)2 (s)
2. Cu(OH)2 is a blue precipitate which dissolves in excess ammonia to form deep blue solution of [Cu(NH3)4(H2O)2]2+ (aq)
State the observations and chemical equation for the reactions between Cr3+ ions and NH3 (aq)
- Cr3+(aq) + 3OH- (aq) →Cr(OH)3 (s)
2. Cr(OH)3 is a green precipitate which dissolves in excess ammonia to form [Cr(NH3)6]3+ (aq) which is a purple solution
How does Fe2+, Fe 3+ and Mn 2+ react with excess aqueous ammonia
- In the same way they react with aqueous sodium hydroxide forming precipitates of Fe(OH)2, Fe(OH)3 and Mn(OH)2
- There is no further reaction with aqueous ammonia and so these precipitates do not dissolve
Describe the redox reaction of Fe2+ (aq) ions and manganate (VII) ions
- In acid conditions it is used as a basis for a redox titration
- 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- (aq) + 8H+ (aq) + 5Fe2+ (aq) →Mn2+ + 5Fe3+ (aq) + 4H2O (l)
Describe the redox reaction between Fe3+ and I-
- When Fe3+ reacts with iodide ions the orange-brown Fe3+ ions are reduced to pale green Fe2+ ions
- This colour change is obscured by the oxidation of iodide ions to form iodine which has a brown colour
- 2Fe3+ (aq) + 2I- (aq) → 2Fe2+ (aq) + I2 (aq)
- Fe3+ is reduced to Fe2+
- I- is oxidised to I2
Describe the redox reactions of dichromate (VI) and chromium ions
- Aqueous dichromate (VI) ions, Cr2O7 2- (aq) have an orange colour
- Cr3+ (aq) have a green colour
- Acidified Cr2O7 2- (aq) ions can be reduced by Cr3+ ions by the addition of zinc. Orange→green
- Cr2O7 2- (aq) + 14H+ (aq) + 3Zn(s) → 2Cr3+ (aq) + 7H2O (l) + 3Zn2+ (aq)
- With excess of zinc Cr3+ ions are reduced further to Cr2+ which is a paler blue colour. Green→pale blue
- Zn(s) + 2Cr 3+ (aq) → Zn 2+(aq) + 2Cr 2+ (aq)
Describe the oxidation reaction of Cr3+
- Hot alkaline H2O2 is a powerful oxidising agent and can be used to oxidise Cr3+ to CrO4 2-
- 3H2O2 + 2Cr3+ + 10OH- → 2CrO4 2- + 8H2O
Describe the reaction of Cu2+ and Cu+ with iodide ions
- When aqueous Cu2+ ions react with excess iodide ions a redox reaction occurs
- I- is oxidised to brown iodine
- Cu2+ is reduced to Cu+
- The Cu+ forms a white precipitate of copper(I) iodide
- 2Cu 2+ (aq) + 4I- (aq) → 2CuI (s) + I2 (s)
Describe the disproportionation reaction of Cu+ ions with H2SO4
- When solid copper (I) oxide Cu2O reacts with hot dilute sulfuric acid, a brown precipitate of copper is formed together with a blue solution of copper (II) sulfate.
- In this reaction copper (I) have been simultaneously oxidised and reduced
- Cu2O (s) + H2SO4 (aq) →Cu(s) + CuSO4 (aq) + H2O (l)
Describe how to identify transition metal ions
- Aqueous sodium ydroxide produced precipitates with aqueous transition metal ions.
- These reactions can be used to identify transition metal ions in an unknown solution
Describe how to identify ammonium ions NH4 +
- When heated with hydroxide ions NH+ reacts to produce ammonia gas NH3
- NH4+(aq) + OH-(aq) →NH3 (g) + H2O (l)
- Gently heat NaOH with the unknown solution and damp red litmus paper will turn blue
Describe how to identify Carbonate ions
- Ass dilute nitric acid
- Effervescence as CO2 is evolved
- CO3 2- (aq) + 2H+ → CO2 (g) + H2O (l)
Describe how to identify sulfate ions
- Add Ba2+ ions
- White precipitate of BaSO4 is formed
- Ba2+ (aq) + SO4 2- (aq) → BaSO4 (s)
