Transition Metals Flashcards
What is transition metal
- transition element is a d block element that can form one or more stable ions with partially filled d orbitals
Atomic radius and ionisation energy are relatively invariant
- nuclear charge increases from Ti to Cu as the number of protons increases
- additional electrons are being added to inner 3d orbitals which causes an increase in shielding effect
- this cancels out the effect due to increase in nuclear charge
- electrostatic forces of attraction of valence electrons from nucleus remains fairly constant
Transition metals have higher melting point compared to s block elements
- have giant metallic lattice structure held together by strong metallic bonds
- in transition metals, both the 3d and 4s electrons are available for metallic bonds since the energy level difference between 3d and 4s orbital is small
- in s block elements, only one or two 4s electrons are available for metallic bonding
- the greater number of delocalised electrons available for metallic bonding in transition elements result in stronger electrostatic attraction between the positively charged ions and ‘sea’ of delocalised electrons
- more energy is required to overcome stronger metallic bonds in transition elements as compared to s block element except Mn with stable d5 arrangement
Transition metals have higher densities compared to s block elements
- transition elements have relatively smaller atomic radii and higher atomic mass compared to s block elements
- have more closely packed structures due to their stronger metallic bonding as compared to s block elements
- transition elements are denser than s block elements
Why transition metals have variable oxidation states in their compounds
- electrons in 3d and 4s subshells are similar in energy
- different number of these electrons are avaliable for use in bond formation
- ions formed by using different number of electrons for bonding are of similar stability
- max oxidation state = 4s electrons + unpaired 3d electrons
Catalytic property of transition elements
— heterogenous catalyst
— homogeneous catalyst
- ability to exist in variable oxidation states
- catalyst should have an electrode potential between those of the reactants
Formation of stable complexes and ligand
- complex consists of a central atom or ion surrounded by anions or molecules called ligands
- ligands is a neutral molecule or an anion that has at least one lone pair of electrons to be used in forming a dative bond to the central metal atom or ion
- all ligands are Lewis bases as they are lone pair donors
Co-ordination number
- total number of dative bonds that are attached to the central atom or ion
Why do transition metal ion form complexes
- transition metal ions have small ionic radius and hence high charge densities,
- attracts ligands that contain lone pair of electrons
- first row transition metal ions have vacant 3d orbitals of low energy level that can accommodate lone pair of electrons from ligands
Isomerism in complexes
— structural isomerism
- ionisation isomerism
- hydration
— stereochemical isomerism
- cis-trans isomerism(square planar, octahedral complexes)
- enantiomerism(octahedral complexes containing at least 2 bidentate ligands)
— conformational isomerism
- different geometries
— polymerisation isomerism
Acidity of transition metal ions in solution
- weak acids
-transition metal ions have high charge density - O-H bonds in H2O ligands are polarised and break
- aqua complex ions undergo partial hydrolysis to give H3O+
Why Sc3+, Ti4+, Cu+, Zn+ are not coloured
- Sc3+, Ti4+ do not have electrons in the d orbitals for d-d transition to occur
- Cu+, Zn+ do not have a partially filled d orbitals in the higher energy level to allow for excitation from lower energy d orbitals
Why are s block elements not coloured
- for s block element to undergo the electron transition, the electron must absorb in the region of very high energy
- 2p-3s transitions are out of the energy range of visible light
- energy from visible light is not absorbed
- solution of Na+ is colourless
Why an aqueous solution of Cr3+ is colourless
- in presence of water ligands, the partially filled 3d orbitals of Cr3+ are split into two different levels with a small energy gap
- when energy is absorbed from the visible light region, an electron is promoted from the d orbital of low energy level to a d orbital of high energy level
- colour of Cr3+ observed is complimentary of the colour absorbed
Why do d-orbitals split into two sets of energy levels in the presence of ligands
- electrostatic repulsion occurs between the lone pair of electrons on the donor atom of approaching ligand and the electrons in d-orbital of transition metal
- strength of repulsion experienced by the 5 d-orbitals is not equal because of the way they arranged differently in space
D-orbital splitting in octahedral complex
- six ligands approach the central metal cation along the x, y and z axes
- since lobes of 3dz2 and 3dx2-y2 orbitals lie along these axis,
- greater electrostatic repulsion occurs between the lone pairs of ligands and electrons in these orbitals and have higher energy level
- smaller electrostatic repulsion occurs between the long pairs of the ligands and electrons in the 3dxy, 3dzx and 3dyz orbitals and they have lower energy level
Factors affecting colours of complex ions
- extent of d orbital splitting in a complex which is measured by magnitude of energy gap determines the colours absorbed and affects the colours observed
- identity of transition metal
- electronic configuration of transition metal ion
- type of ligands
