transition elements Flashcards
what is a transition element?
a d-block element which forms one or more stable ions with partially filled d subshells
(by this definition, Sc and Zn are not transition elements since they do not form ions with a partially filled subshell)
why are the atomic radii and 1st IE of the transition elements relatively invariant?
- no. of proton increases, NC increases
- e- are added to inner 3d subshell, inner 3d e- effectively shield outer 4s electrons from the nucleus, cancelling the effect of the increasing NC across the period
- increase in ENC is insignificant, atomic radii and 1st IE remains almost constant
how does the melting point of transition elements compare to s-block elements (e.g. calcium)
first row transition elements have a higher mp than s-block elements
both have giant metallic structures, but transition elements have stronger metallic bonds due to:
- availability of 3d e- for delocalisation in the sea of electrons
- smaller cationic radius
hence more energy is required to overcome the stronger electrostatic forces of attraction
how does the densities of transition elements compare to s-block elements (e.g. calcium)?
transition elements are denser than s-block elements, due to smaller cationic size, higher mass, and stronger metallic bonds resulting in closer packing
why are transition elements able to exhibit various oxidation states?
due to the close proximity of energy of the 4s and 3d electrons
what is a complex?
CDL
a complex is a central metal atom or ion dative bonded to one or more surrounding molecules or anions called ligands
if it has an overall charge, it is a complex ion
what is a ligand?
ILDD
- an ion or molecule,
- which contains at least 1 atom with a lone pair of electrons,
- which can be donated into a low-lying vacant orbital of a central metal atom or ion
- to form a dative covalent bond, resulting in the formation of a complex
what are the different types of ligands?
- monodentate ligand (forms 1 dative bond to a central atom)
- polydentate ligand e.g. bidentate ligand, tetradentate ligand
what is ligand exchange?
when one ligand displaces another ligand from the metal complex
describe what happens when dilute NH3 (aq) is added to a solution containing Cu2+ (aq) until in excess
when dilute NH3 (aq) is gradually added, a blue ppt of Cu(OH)2 is first formed
NH3 + H2O ⇌ NH4+ + OH-
[Cu(H2O)6]2+ (aq) + 2OH- (aq) ⇌ Cu(OH)2 (s) + 6H2O (l) ——- eqm 1
when excess NH3 (aq) is added, ligand exchange occurs to form a deep blue solution
[Cu(H2O)6]2+ + 4NH3 ⇌ [Cu(NH3)4(H2O)2]2+ + 4H2O ——- eqm 2
The formation of [Cu(NH3)4(H2O)2]2+ decreases the conc of [Cu(H2O)6]2+, causing the POE of eqm 1 to shift to the left to replenish. thus blue ppt Cu(OH)2 dissolves, forming deep blue solution
why does the intake of carbon monoxide deplete oxygen levels?
CO is a stronger ligand than O2, so CO displaces O2 in haemoglobin
CO also bonds less reversibly to haemoglobin
what are the colours of copper compounds?
[Cu(H2O)6]2+ : blue
[CuCl4]2-: yellow
[Cu(NH3)4(H2O)2]2+: deep blue
Cu(OH)2: pale blue
CuCl, CuI: white ppt
Cu2O: brick red ppt
describe the splitting of d orbitals into two energy levels
IOEEGS
1) difference between energy level of gas phase and octahedral complex + reason
2) which d orbitals have higher energy level + reason
3) results in?
- in the isolated gas phase, all five partially filled d orbitals are degenerate (have the same energy)
- in octahedral complexes, the energy of the d orbital is higher that that in the gas phase ion
- this is due to electronic repulsion between the lp of e- of the ligands and the e- in the d orbitals
- the energy of the 3dx2-y2 and 3dz2 orbital is greater than the 3dxy,3dxz and 3dyz orbitals
- this is due to greater electronic repulsion due to the ligands approaching the central ion along the axes
- this results in the d orbitals splitting into 2 energy levels with a small energy gap between them
explain why a solution is coloured.
- in the presence of aqua ligands, the partially filled d orbitals split into 2 energy levels
- when an electron from the lower energy d orbitals is promoted to a higher energy d orbital, visible light is absorbed
- the colour not absorbed is observed
why are some ions containing transition elements colourless?
- no 3d electrons, hence no d-d transition to exhibit coloured complex
- 3d subshell is fully filled, no vacancy in the higher d-orbitals, no d-d transition