6.10 transition elements Flashcards
define transition elements
a transition element is a d-block eleent which forms one or more stable ions with partially filled d-subshells
what are the exceptions d-block elements which are not transition metals?
Sc and Zn
what are the exceptions of elements with strange configurations?
Cr and Cu
why are transition metals able to exhibit variable oxidation states, and how do you find the maximum oxidation state a metal can exhibit?
the 4s and 3s electrons are similar in energy, hence once all 4s electrons are removed, some or all 3d electrons may also be removed without much more energy
max OS: no. of 4s e + no. of unpaired 3d e (max 7)
why does atomic radius and 1st IE remain relatively constant across transition metals?
across the group, electrons are added to the penultimate 3d orbital, hence shielding effect increases which cancels out the increase in nuclear charge. effective nuclear charge remains relatively constant
why are transition metals denser than s-block metals?
transition metals have larger atomic mass and smaller atomic radius, hence more mass per unit volume
why do transition metals have higher melting and boiling points than metals?
s-block metals only have 2 valence electrons delocalised while transition metals can delocalise up to 12 electrons, more energy required to overcome stronger metallic bonding
define a complex
a molecule consisting of a central atom or ion surrounded by ligands bonded to it by dative bonds
define a ligand
ligand is a neutral molecule or anion containing at least one atom with a lone pair of electrons that can be donated to form a dative bond with a metal atom or ion
describe d-orbital splitting in transition elements
in the presence of ligands, all 5 d-orbitals are destabilised and hence have higher levels than original.
dx2-y2 and dz2 orbitals have lobes that are in the region of ligands along the x,y and z axis, hence there is greater repulsion between the orbitals and the lone pair(s) on ligands. the orbitals are destabilised to a greater extent and have higher energy levels than dxy, dyz and dxz orbitals.
the dxy, dyx and dxz orbitals have lobes in between regions of ligands, hence there is less repulsion.
hence in the presence of light, there is the splitting of d-orbitals into 2 different energy levels.
explain why transition element compounds are coloured
in the presence of ligands, the orbitals of the transition metal ion are split into two groups of different energy levels. when white light shines on the complex, a d electron is PROMOTED to a higher energy VACANT OR PARTIALLY FILLED d-orbital. during this transition, the d electron absorbs a wavelength of light from the visible spectrum. the transmitted light, which is complementary to the wavelength of the light absorbed, gives the transition metal complex its colour.
what are the factors affecting colour of a transition compound?
- identity of metal and oxidation state
- shape of complex ion (tetrahedral is dxy,dyz,dxz orbitals higher energy)
- nature of ligand (stronger ligands, stronger repulsion, larger energy gap)
what reactions can transition compounds undergo? (4)
- precipitation
- oxidation
- acid-base (due to partial hydrolysis)
- ligand exchange
describe how transition metal works as a heterogenous catalyst
reactant molecules diffuse towards and are adsorbed on active sites of the transition metal. this increases the concentration of reactant molecules on the active site, and orientates them in the correct orientation. intramolecular bonds are weakened, thus lowering activation energy. after reaction occurs, products desorb and diffuse away from the metal to free up active sites for further reaction.
