Transition Elements Flashcards
What are the types of d-orbitals in transition metals?
dxy,dxz, and dyz have d-orbitals in between axes; dx2-y2 and dz2 have d-orbitals along axes.
Dz2 is formed by the merging of dx2-z2 and dy2-z2
What causes variable oxidation states in transition metals?
The small energy difference between 4s and 3d allows electrons from both subshells to be removed, forming various oxidation states.
Transition metals have partially filled d-orbitals, leading to variable oxidation states.
All transition metal exhibit two or more oxidation states
What is the most common oxidation state of transition metals?
The most common oxidation state is +2 when 2 electrons from 4s are lost.
When do transition elements exhibit their highest oxidation states?
Transition elements show the highest oxidation states when they combine with oxygen or fluorine as they are the most electronegative.
What types of compounds do transition elements form in high oxidation states?
In high oxidation states above +4, they form large oxyanions and covalent compounds (acidic oxides) like CrO4 or MnO4.
What types of compounds do transition elements form in lower oxidation states?
In lower oxidation states, they form ionic compounds (basic oxides).
What is a complex in chemistry?
A complex is an ion or molecule formed by a central metal atom/ion datively bonded by one or more ligands.
Transition elements can form complex ions because d orbitals are energetically accessible.
A complex consists of
a central transition metal ion (+ve) that can accept electrons and
Ligands (-ve) which is a species that contains a lone pairs of electrons that forms a dative bond to a central metal atom/ion.
What are the components of a complex?
A complex consists of a central transition metal ion that can accept electrons and ligands that donate lone pairs of electrons.
What is the coordination number in a complex?
The coordination number is the number of coordinate or dative bonds being formed by the central metal atom/ion.
Different metal ions show different coordination number with same ligands.
Why do transition metals form complexes?
Transition metals form complexes because:
Ions are small in size so they have a strong electric field around them which attracts electron-rich ligands.
They have empty 4s and 4p orbitals that are hybridised and can accept electrons.
What are monodentate ligands?
Monodentate ligands form only one coordinate bond with the central metal ion, donating one pair of electrons.
Examples include halide ions (F-, Cl-, Br-, I-), sulfide (S2-), nitrite (NO2-), hydroxide (OH-), cyanide (CN-), and thiocyanate (SCN-).
Neutral ligands include water (H2O), ammonia (NH3), and carbonyl (CO).
What are bidentate ligands?
Bidentate ligand is a species with two lone pair of electrons that forms co-ordinate/dative covalent bonds to a central metal atom/ion.
Ethylene diamine (en) is a neutral bidentate ligand that forms 6 coordinate bonds.
Oxalate ion (oxalato-)
How do we write formulae of complexes
*Metal ion written first followed by ligand
*Place charge on formula in square br
*Total charge on complex= sum of charge on metal ions and charge on ligand
*If ligands all neutral, charge on complex= charge on metal ion
Describe the shapes of complexes with their coordination number and shape
Coordination number is 6 and shape octahedral with bond angle 90. Non polar.
Coordination number is 4 and shape tetrahedral with bond angle 109.5
Coordination number is 4 and shape square planar and bond angle 90. This happens when the ligands consists of two or more atoms and usually the central atom is Ni and Pt). Polar.
Coordination number is 2 and shape linear and bond angle 180. Non polar.
What is cis-platin?
Cis-platin is an anticancer drug that acts by binding to DNA in cancer cells, preventing cell division. Trans-platin will not have the same beneficial medical effects.
What are geometric isomers?
Molecules or ions with the same molecular formula and the same molecular formula and same bonds between their atoms but which cannot be superimposed on each other, due to some lack of rotation around their bonds.These are also known as cis/trans isomers.
Describe the differences in electronegativity in geometrical isomerism
Cis isomers will have two identical groups on one side of any square planar complex. So any difference in electronegativity between the two pair of isomers will cause an imbalance of charge making a polar complex.
However, the trans isomer will have identical lies directly opposite each other at the corners of the square planer complex so the charge is balanced and results in a non-polar complex.
What is stereoisomerism?
Two isomers that are mirror images of each other and cannot be super imposed. They are optical isomers. They differ only in their ability to rotate the plane or polarise light in opposite directions.
Stereoisomerism is commonly shown by octahedral complexes associated with bidentate ligands.
What is the reaction of Cu2+ (aq) with hydroxide ions?
[Cu(H2O)6]2+(aq)+2OH-(aq) ➡️ Cu(OH)2(H2O)4(s) + 2H2O(l)
Blue solution turns to pale blue precipitate
Not ligand exchange, hydroxide ions remove hydrogen ions from water ligand?
What is the reaction of CU2+ (aq) with ammonia solution?
Small amounts of ammonia
[Cu(H20)6]2+ +2NH3 ➡️ Cu(H2O)4(OH)2 + 2NH4+
blue solution turns into pale blue precipitate
Initially, ammonia act as a base and hydrogen ions are pulled off the hexaaqua ions as above
Excess ammonia:
Cu(H2O)4(OH)2 + 4NH3 ➡️ [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-
Pale blue pot turns into deep blue solution
Ammonia replaces water as ligand
Only 4 of 6 water molecules replaced
What is the reaction of CU2+ (aq) with chloride ions?
If we add hydrochloric acid drop by drop
[Cu(H2O)6]2+(aq) + 4Cl- (aq) 🔄 [CuCL4]2- (aq) + 6H2O (l)
Blue solution changes to yellow solution
The mixture of blue and yellow solution in the reaction mixture gives a greenish colour.
What is the reaction of Co2+ (aq) with hydroxide ions?
[Co(H2O)6]2+ (aq) + 2OH- (aq) ➡️ Co(OH)2(H2O)4(s) +2H2O (l)
Pink solution turns to blue precipitate
Blue precipitate turns red when warmed if the alkali is in excess
What is the reaction between Co2+ (aq) and concentrated aqueous ammonia drop by drop?
[Co(H2O)6]2+(aq) + 6NH3 (aq) ➡️ [Co(NH3)6]2+ (aq) + 6H2O (l)
Pink solution turns into brown solution
What is the reaction between Co2+(aq) and concentrated hydrochloric acid drop by drop?
[Co(H2O)6]2+(aq) + 4Cl- (aq) ➡️ [CoCl4]2- (aq) + 6H2O (l)
Pink solution to blue solution
What is ligand exchange?
A more powerful ligand will substitute a less powerful ligand from a cation of the complex and this can produce a change in colour and shape.
Exchange of ligands can be explained in terms of competing equilibrium of forward and backward reactions. Equilibrium position lies towards more stable complex. Adding excess weak ligand can shift equilibrium backward and form weaker complexes.
What is the stability constant Kstab?
The stability constant is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions or molecules.
Water is not include in Kstab expression because concentration is almost constant.
Stability constants are used to compare stability of any two ligands.
The greater the stability value the more stable the complex.
Kstab values may be given off on logo scale as values large. When expressed by log10 they have no units.
Stability constants for complexes with bi/polydentate ligands are very high.
What is the energy state of the five d-orbitals in isolated transition metal atoms/ions?
The five d-orbitals are degenerate; all at the same energy.
What happens to d-orbitals when ligands coordinate bond?
The five d-orbitals split into two sets of non-degenerate orbitals at ΔE.
How do ligands affect the energy of d-orbitals in octahedral complexes?
Ligands approach along the axis, increasing repulsion with dx2-y2 and dz2 orbitals, causing them to be at higher energy.
What occurs when electrons from lower energy orbitals absorb energy?
Electrons absorb energy equal to ΔE from light and are excited to a higher energy level orbital.
What happens to wavelengths of light in relation to ΔE?
Wavelengths of light equivalent to ΔE are absorbed, and the rest are transmitted.
The wavelengths transmitted merge together to correspond to the color of the solution.
What are the conditions for a complex to be colored?
At least one d-orbital must be occupied by an electron, and at least one d-orbital must not be fully occupied.
All Sc compounds are colorless because they have [Ar] 3d0, and all Zn compounds are colorless because they have [Ar] 3d10.
What factors determine the color of a complex?
The factors include the magnitude of ΔE, strength of ligands, oxidation state of the metal ion, and geometry of the complex.
How does ΔE relate to the color of the complex?
A large ΔE means light absorbed from blue, resulting in a red-ish complex; a small ΔE means light absorbed from red, resulting in a blue-ish complex.
Suggest why a transition metal may form a colourless ion
Due to the oxidation state there may be no electrons or a full electrons in the de orbital. It cannot absorb photons/light in visible spectrum.
What are the properties of transition metals?
- They have variable oxidation states
- They behave as catalysts
- They form complex ions
- They form coloured ions
- They have high melting points
- They have h de
nsities - They are hard and rigid and so are useful as construction
What is the oxidation state of zinc
Zinc only has an oxidation state of 2+
Iron is a transition element. Explain why iron forms stable compounds in both the +2 and +3 oxidation states.
Similar energy of the 3d and 4s orbitals.
Explain why different complex ions form different colours. (2)
ΔE different or (d-do energy gap different
Different frequency/wavelength/energy from visible light absorbed.
Which shapes of complexes show geometrical isomerism?
Square planar and octahedral
Which shapes of complexes show optical isomerism?
Tetrahedral and linear (sometimes octahedral)
Define transition elements
Forms one or more stable ions/compounds/oxidation states with incomplete/partially filled d-subshell/d-orbitals.
Using Le Chateliers principle explain why a ppt is formed when NaOH is added dropwise to [Cu(NH3)4(H2O)6]2+
Addition of OH- increases [OH-] and shift’s equilibrium to the right.
