transition metals Flashcards
what is a transition metal
a transition element is a d-block element that has an incomplete d-sub-shell as a stable ion
why are scandium and zinc not transition metals
scandium and zinc are the first and last members of the period 4 d-block elements and are not classed as transition metals because they do not have any ions partially filled d-orbitals
- scandium forms only Sc3+ ion in which the d-orbitals are empty
- zinc only forms the Zn2+ ion which the d-orbitals are full
transition element electronic configuration rules
- the sub shell energy levels in the third and fourth energy levels overlap
- the 4S sub shell fills before the 3d sub shell
describe when the electronic configuration pattern breaks
- breaks for chromium and copper, in order to reduce the electron repulsion between the outer electrons resulting in increased stability for the copper and chromium atoms
- chromium - the 5 3d orbitals and 4s orbitals all contain one electrons with no orbital being completely filled
- cooper the 5d orbitals are filled but there is only one electron in the 4s orbital
what happens in reactions of transition elements
- in the reactions transition element atoms lose electrons to form positive ions
- they lose their 4s electrons before there 3d electrons
- this is because the 3d and 4s energy levels are close together and once electrons occupy the orbitals the 4s electrons have a higher energy and are lost first
what are the physical properties of transition metal compounds
- transition elements are all metals,
- high densities
- high melting and boiling points
- exist as giant metallic lattices
- contain delocalised electrons so can conduct electricity
what are the chemical properties
- they have different oxidation states
- transition metals form coloured solutions when dissolved in water
- catalyse chemical reactions - due to partially filled d-orbitals
describe the variable oxidation states for transition elements
- the transition elements from titanium to copper all form ions with more than one stable oxidation state
- these metals also all form compounds with metal ions in the +2 oxidation state, this results from loosing two electrons in the 4s orbital
- the highest oxidation state of a transition element is found in a strong oxidising agent,
describe coloured compounds
- when white light passes through a solution containign transition metal ions some of the wavelengths of visible light are absorbed, the colour that we observe is a mixture of the wavelengths of light that have not been absorbed
- for example a solution of copper sulfate appears pale blue becasue the solution absorbs the red/orange region of the electromagnetic spectrum and reflects or transmits the blue
- colour is linked to the partially filled d-orbitals of transition metal ions
why does scandium(III) not have a coloured compound
- scandium does not have d shell and is colourless in aqueous solution, scandium III is formed from scandium by the loss of 2 4s electrons and one 3d electron there is no partially filled d-orbital and there is no colour
describe how transition metals act as catalysts
- they provide a surface on which a reaction can take place, reactants are adsorbed onto the surface of the metal and held in place while a reaction occurs, after the reaction the products are desorbed an d the metals remain unchanged
- transition metal ions have the ability to change their oxidation states by gaining or losing electrons, they bind to reactants forming intermediates as part of a chemical pathway often with a lower activation energy which speeds up the reaction
describe transition metals as industrial catalysts
- transition metal catalysts are used in industry to improve the profits of an industrial process, they can reduce the time it takes to make a product and reduce the amount of energy needed to make the reaction occur
- toxic
- when substances bind to the active site and stop the transition metal catalysts from working the catalysts can no longer be used, must be disposed of in a way that does not cause harm or pollution
describe haber process
- used to make ammonia from the reaction of nitrogen and hydrogen
- catalyst is an iron metal - used to increase the rate of reaction and to lower the temperature at which the reaction takes place
- much of the ammonia produced in the Haber process is used in manufacturing agricultural fertilisers
describe the contact process
- used to convert sulfur dioxide into sulfur trioxide which is used to manufacture sulfuric acid
- 2SO2 + O2 = 2SO3
- vanadium oxide in which vandium has the +5 oxidation state
- sulphuric acid is an important inorganic chemical with many uses including the production of fertilisers, detergents, adhesives and explosives and also as the electrolyte in car batteries
describe the hydrogenation of alkenes
- hydrogen can be added across the C=C double bond in unsaturated compounds
- nickel metal - it is used to lower the temperature and pressure needed to carry out the reaction
- process is used in the hydrogenation of unsaturated vegetable oils to make spreadable margarines
decomposition of hydrogen peroxide
- hydrogen peroxide decomposes slowly at room temperature and pressure into water and oxygen
- catalyst is added to increase the reaction rate
- 2H2O2 = 2H20 + O2
- manganese (IV) oxide MnO2, this is when manganese has the +4 oxidation state
- often called manganese dioxide
- used in laboratory as a simple way of making oxygen gas
describe hydrogen production
- zinc granules will react with dilute sulfuric acid to form hydrogen and zinc sulfate
- when copper(II) sulfate is added the rate of reaction increases
- transition metal ion acts as a catalyst
- Zn + H2SO4 = ZnSO4 + H2
- reaction used to produce hydrogen gas
what is a complex ion
this is a transition metal ion bonded to one or more ligands coordinate bonds (dative covalent bonds)
what is a ligand
- this is a molecule or ion that can doante a pair of electrons to the transition metal ion to form a coordinate bond
what is a coordination number
- this is the total number of coordinate bonds formed between a central metal ion and its ligands
what does a transition metal do to accept a ligand
- it accepts the pair of electrons from the ligand and forms the coordinate bond
in the formula of a complex ion…
- the square brackets group together the species making up the complex ion
- the overall charge is shown outside the brackets
the overall charge is ….
the sum of the individual charges of the transition metal ion and those of ligands present in the complex
what happens in a monodentate ligand
- the ligand donates just one pair of electrons to the central metal ion to form one coordinate bond
what happens n a bidentate ligand
- bidentate ligands have two pair of electrons from different atoms to donate to the central metal, therefore two coordinate bonds can be formed
- NH2CH2CH2NH2 - usually shortened to en
- each nitrogen atom donates its lone pair to the metal ion
name some neutral ligand
- OH2
- NH3
name the negative ligands
- SCN-
- CN-
- Cl-
- OH-
what is the uses of EDTA
- in detergents - binds to calcium and magnesium ions to reduce hardness in water
- in some foods - as a stabiliser to remove metal ions that might catalyse the oxidation of the product
- in medical applications - it is added to blood samples to prevent clotting and used to treat patients suffering from lead and mercury poisoning
what is a mutlidentate ligand
- a hexadentate ligand has six lone pairs of electrons avaliable to form coordiante bonds
describe EDTA and draw it
- hexadentate lignad
- exosts in complexes as the ion EDTA 4-
- EDTA is used to bind metal ions and is known as chelating agent, this means that EDTA decreases the concentration of metal ions in solutions by binding them into a complex
describe the octahedral shape of a complex ion
- has 6 coordinate bonds attached to the central ion
- the outer face of the shape is an eight sided octahedron, 4 of the ligands are on the same plane, one ligand is above the plane and the remaining are blow the plane - has the bond angles 90 or 180
draw [Co(H2O)6]2+
draw it
draw the 3d octahedral shape
draw it
- the solid wedge bonds come out of the plane of the paper towards you
- the hatched wedge bonds go into the plane of the paper away from you
- the ligands attached by the wedge bondsa re at teh corners of a sqaure with each bond separated by 90 degrees
- the solid lines represent bonds in the plane of the paper
- the oslid bonds are separated by wedge bonds by 90 degrees
describe octahedral complexes with mutlidentate ligands
- each en ligand forms two coordinate bonds to the central metal ion
- there are three en ligands giving a total of 3x2 = 6 coordiante bonds
- the coordination number is 6
describe chloride ions as ligands
- chloride ligands are so large that only 4 can fit around a transition metal ion so chlroide complexes form a tetrahedral shape
what are square planar complex
- a rare configuration is a square planar complex, this is when the four monodentate ligands arrnage themselves in the same plane as the metal atom
what is cis platin
- cis plantin is the cis-isomer of a plantinum complex [PtCl2(NH3)2]
- square planar
- effective against cancer
what is a stereoisomer
this is species with the same structural formula but with a different arrangement of the atoms in space
what are the two types of steroisomeism transition element
- cis-trans
- optical
what are the two different octahedral complex ions ligands
- four monodentate ligands and two different monodentate ligands
- two bidentate ligands and two different bidentate ligands
- these exist as cis and trans isomers
describe early examples of steroisomerism
- early examples of sterioisomerism involves Co3+ complex ions
- Sophus Mads Jorgensen observed that some complex ions could form salts that had different colours
who succeeded in explaining the existence of two isomers
- Alfred werner
- werner propsed that there were two isomers of [Co(NH3)4Cl2]+
- one was purple and one was green
- he suggested that the cobalt (III) ion was surrounded by 4 NH3 ligands and 2Cl- ligands at the corners of an octahedron
he called the purple isomer cis
- the two Cl- ligands are at adjacent corners of the octahedron
- the two Cl- ligands are at 90 degrees to one another
he called the gren isomer trans
- the two Cl- ligands are at opposite corners of the octahedron
- the two Cl- ligands are at 180 to each other
what other shape is cis trans isomerism possible in
- 4 coordinate complexes - square planar shape
- the complex must contain two different ligands with two of one ligand and two of another
How does cis platin work
- it acts by binding to the DNA of fast gorwing cancer, preventing cell division and prevents the cells from reproducing by changes to the DNA strucutre
- activation of cells own repair mechanism leads to death of cancer containing cells
- used in chemotherapy
- now developing a new generation of compounds with lower doses and fewer side effects such as carboplatin which treats ovarian cancer by slowing down cancer growth by reacting with a cells DNA
whats the negatives of cis platin
- severe sickness
- hair loss
- fatigue
if they are close together then they are
cis
if they are far apart than they are
trans
what are the requirements for optical isomerism
- a complex with three molecules or ions of a bidentate ligand
- a complex with two molecules or ions of a bidentate ligand and two molecules or ions of a monodentate ligand
- a complex with one hexadentate ligand
describe optical isomers
- they are non superimposable mirror images of each other
- they rotate plane-polarised light differently, one of the isomers rotates the light clockwise and the other anticlockwise
whats a racemic mixture
- this is a mixture containing equal amounts of two optical isomers and has no effect on plane-polarised light because the rotations cancel out
