Transition elements Flashcards
Describe d-block elements
-found in the middle of the periodic table
-some elements are transition metals
what is a transition element?
d-block element that can form at least one stable ion with a partially filled (incomplete) d-subshell
d-subshell can hold up to how many electrons?
10
How does chromium and copper behave differently in electron configuration compared to other transition elements in period 4?
An electron from the 4s orbital moves into the 3d orbital to create a more stable half full (Cr) or full 3d sub-shell respectively (Cu)
Why is scandium not a transition element?
-scandium forms ion Sc3+
-Sc3+ has an empty d-subshell. As it is not partially filled, it is not a transition element
Why is zinc not a transition element?
-Zinc forms ion Zn2+
-Zn2+ has a full d-subshell. As it is not partially filled, it is not a transition element.
How do transition metals lose electrons in a specific way to form ions?
lose from 4s first then 3d
What are the properties of transition metals?
-variable oxidation states
-form coloured ions in solution
-good catalysts
Why do transition metals have variable oxidation states?
because the electrons sit in the 4s and 3d energy levels which are very close. As a result, electrons are gained and lost using a similar amount of energy when they form ions
V 2+ colour?
violet
V 3+ colour?
green
VO 2+ colour?
blue
Cr 3+ colour?
green
Cr2O7 2- colour?
orange
Mn2+ colour?
pale pink
MnO4 2- colour?
green
MnO4- colour?
purple
Fe2+ colour?
pale green
Fe3+ colour?
yellow
Co2+ colour?
pink
Ni2+ colour?
green
Cu2+ colour?
blue
Ti2+ colour?
violet
Ti3+ colour?
purple
Why are transition metals good catalysts?
-as they have variable oxidation states they are good catalysts by receiving and losing some electrons in the d-orbitals to speed up reactions
-transition metals have surfaces that allow substances to adsorb which lowers activation energy. Product can be made faster and temperature can be lowered for a reaction which saves energy money and better for environment
What are the risks when using transition metals as catalysts?
-copper long term exposure can cause liver damage
-long term manganese exposure can cause psychiatric issues and physical tremors
How does MnO2 (transition metal) act as a catalyst?
MnO4 catalyses hydrogen peroxide decomposition.
2 H2O2 -> 2 H2O + O2
How does Fe acts as a catalyst?
Fe catalyses the haber process making ammonia.
3 H2 + N2 -> 2NH3
How does CuSO4 act as a catalyst?
CuSO4 catalyses zinc + acid reactions.
Zn + H2SO4 -> ZnSO4 + H2
What is the formula for a complex ion?
[M(H2O)6] n+ which can be simplified to M n+
What is a complex ion?
consists of a central metal ion bonded to ligands by coordinate bonds
Coordination number definition?
number of coordinate bonds attached to a central metal ion
Ligand definition?
molecule or ion that donates a pair of electrons to a central metal ion to form a coordinate bond or dative covalent bond
What change occurs when OH- or NH3 is added to [Cu(H2O)6]2+?
[Cu(H2O)6]2+(aq) blue -> Cu(OH)2(H2O)4(s) pale blue precipitate
-there is no change to the precipitate in excess NaOH
-When excess NH3 is added to the precipitate, [Cu(NH3)4(H2O)2]2+(aq) is formed (dark blue solution), part ligand substitution
What change occurs when OH- or NH3 is added to [Fe(H2O)6]2+?
[Fe(H2O)6]2+(aq) pale green -> Fe(OH)2(H2O)4(s) dirty green precipitate
-there is no change to the precipitate in excess NaOH
-there is no change to the precipitate in excess NH3
What change occurs when OH- or NH3 is added to [Fe(H2O)6]3+?
[Fe(H2O)6]3+(aq) yellow -> Fe(OH)3(H2O)3(s) orange precipitate
-there is no change to the precipitate in excess NaOH and in excess NH3
What change occurs when OH- or NH3 is added to [Mn(H2O)6]2+?
[Mn(H2O)6]2+(aq) pale pink -> Mn(OH)2(H2O)4(s) pink precipitate
-there is no change to the precipitate in excess NaOH and in excess NH3
What change occurs when OH- or NH3 is added to [Cr(H2O)6]3+(aq)?
[Cr(H2O)6]3+(aq) green -> Cr(OH)3(H2O)3(s) green-grey precipitate
-When excess OH- is added to the precipitate, Cr(OH)6 3-(aq) a dark green solution is formed
-When excess NH3(aq) is added to the precipitate, Cr(NH3)6 3+(aq) purple solution
Describe complex ion solution equations
reactants: +OH- OR +NH3 (2 moles if ion has 2+ charge, 3 moles if ion has 3+ charge)
products: H2O (2 moles if ion has 2+ charge, 3 moles if ion has 3+ charge)
What are monodentate (unidentate) ligands? provide examples
ligands which only have one pair electrons . E.g H2O, NH3, CN-, Cl-
What are bidentate ligands? provide examples
ligands which have 2 lone pairs of electrons. E.g ethanedioate, ethane-1,2-diamine
What are multidentate ligands?
ligands which have more than one coordinate bond. E.g EDTA 4-, it can form 6 coordinate with the central metal ion
How is the shape of a complex ion determined?
shape is dependent on the size of the ligands and the coordination number
Which ligands are small, meaning you can fit 6 of them around the central metal ion?
H2O, NH3 and CN-
Which ligand can you fit 4 around the central metal ion?
Cl-
Which ligand can you fit 3 around the central metal ion?
ethanedioate and ethane-1,2-diamine
Complexes with coordination number of 6 forms what shape?
octahedral shape, all bond angles are 90 degrees
complexes with a coordination number of 4 form what shape? provide a specific example
forms tetrahedral and square planar shapes.
-bond angles in a tetrahedral complex are 109.5 degrees
-bond angles in a square planar complex are 90 degrees
-anti-cancer drug, cis-platin is a square planar complex
How do you calculate the overall charge/oxidation state of a complex ion?
oxidation state of metal - total oxidation state of ligands
complex ions which are optical isomers are?
mirror images e.g octahedral complexes with 3 bidentate ligands
Describe cis-trans isomerism in complex ions, octahedral complexes
-octahedral complexes with 4 ligands of the same type and 2 of a different type display cis-trans isomerism
-if the 2 different ligands are opposite each other, you have a trans isomer
-if the 2 different ligands are adjacent each other, you have a cis isomer
Describe cis-trans isomerism in square planar complex ions
-square planar complexes with 2 ligands of the same type and two ligands of a different type display cis-trans isomerism
-If the two different ligands are opposite each other, you have a trans isomer
-If the two different ligands are adjacent each other, you have a cis isomer
Describe cis-platin
-anti-cancer drug which is a square planar complex with a platinum metal ion, 2 ammonia ligands and two chloride ion ligands.
-chloride ions in complex and easy to displace therefore bonds with nitrogen atoms on DNA of cancer cell can form. This attachment prevent cell division
-however cis-platin can prevent cell division of heathy cells, suppressing the immune system
What occurs when a complex ion reacts with a ligand of similar size? Use example of [Co(H2O)6]2+ and NH3
substitution reaction occurs and shape doesn’t change (octahedral)
[Co(H2O)6]2+(aq) pink + 6 NH3(aq) -> [Co(NH3)6]2+(aq) STRAW COLOUR + 6H2O(l) full substitution of all ligands has occurred
What occurs when a complex ion reacts with a ligand of a different size?
there is a change in shape and coordination number
What are the changes in colour and shape when [Co(H2O)6]2+(aq) reacts with Cl-(aq)(larger ligand)?
[Co(H2O)6]2+(aq) PINK AND OCTAHEDRAL + 4Cl-(aq) -> [CoCl4]2-(aq) BLUE AND TETRAHEDRAL + 6 H2O(l)
What are the changes in colour and shape when [Cu(H2O)6]2+(aq) reacts with Cl-(aq)(larger ligand)?
[Cu(H2O)6]2+(aq) BLUE AND OCTAHEDRAL + 4 Cl-(aq) -> [CuCl4]2-(aq) YELLOW AND TETRAHEDRAL + 6 H2O(l)
What are the changes in colour and shape when [Fe(H2O)6]3+(aq) reacts with Cl-(aq)(larger ligand)?
[Fe(H2O)6]3+(aq) YELLOW AND OCTAHEDRAL + 4Cl-(aq) -> [FeCl4]-(aq) YELLOW AND TETRAHEDRAL + 6 H2O(l)
describe NH3
NH3 IS ONLY USED AS A BASE. IT ACTS AS A LIGAND IN EXCESS
three bidentate ligands give what kind of isomerism?
optical isomerism (2 mirror images)
2 bidentate ligands + 2 monodentate ligands give what kind of isomerism?
optical isomerism (2 mirror images) and geometrical isomerism
how is ammonia solution made?
NH3(g) + H2O(l) -> NH4OH(aq)
NH4+(aq), OH-(aq)
the colour of complex ions depends on what?
the size of the energy change which is affected by change of oxidation state, co-ordination number and change of ligand
Describe the structure of haemoglobin?
-haem is a multidentate ligand that is found in the molecule haemoglobin
-octahedral structure
-one of the co-ordinate bonds come from a protein called globin
-the final coordinate bond comes from either an oxygen or water molecule
How does haemoglobin work?
-oxygen substitutes the water ligand to form oxyhemoglobin
-In a place where oxygen is needed, oxyhemoglobin gives up oxygen and water takes the place
Explain how carbon monoxide affects haemoglobin?
-the water ligand is replaced with carbon monoxide
-carbon monoxide bonds strongly so its not readily replaced by oxygen or water. This leads to oxygen starvation
how are metal-aqua complexes formed?
when we add transition metal compound to water
How can we identify transition metals?
by adding sodium hydroxide solution and observing the colour of the precipitate formed
what colour precipitate does Cu2+ form in NaOH solution?
blue precipitate
what colour precipitate does Fe2+ form in NaOH solution?
green precipitate
what colour precipitate does Fe3+ form in NaOH solution?
orange precipitate
what colour precipitate does Mn2+ form in NaOH solution?
pink precipitate
what colour precipitate does Cr3+ form in NaOH solution?
dirty green precipitate
