Summary Unit 3.2.5 - Transition metals (A-level only)
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Course
Unit 3.2.5 - Transition metals
Institution
AQA
Detailed notes on the AQA A level chemistry topic transition metals. General properties are discussed along with metal complexes, optical isomerism, cis-trans isomerism, d-orbital splitting, coloured complexes, transition metal complex colours, colorimetry, vanadium chemistry, Tollen's reagents, ca...
Transition metals
General properties of transition metals
Transition metal characteristics of elements Ti–Cu arise
from an incomplete d sub-level in atoms or ions.
The characteristic properties include:
• complex formation
• formation of coloured ions
• variable oxidation state
• catalytic activity.
A ligand is a molecule or ion that forms a co-ordinate bond
with a transition metal by donating a pair of electrons.
A complex is a central metal atom or ion surrounded by
ligands.
Co-ordination number is number of co-ordinate bonds to
the central metal atom or ion.
A transition element is a d-block element that can form at least one stable ion with a
partially filled (incomplete) d-subshell.
for the period 4 d-block elements, only 8 of these are transition elements
scandium and zinc are NOT transition elements - because they don't form a stable ion
with a partially filled d sub-shell
Electronic configurations:
chromium and copper behave differently - an electron from the 4s orbital moves into the
3d orbital to create a more stable half full or full 3d sub-shell respectively.
Cr - 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5
Scandium forms only 1 stable ion of Sc3+
Sc3+ has an empty d-subshell - it is not partially filled so it is not a transition metal
Transition metals 1
, Zinc forms only 1 stable ion of Zn2+
Zn2+ has a full d-subshell - it is not partially filled so it isn't a transition metal.
when forming ions, transition metals lose electrons from 4s and then 3d
Properties of transition metals
transition metals have specific properties which include variable oxidation states, form
coloured ions in solution and are good catalysts.
They have variable oxidation states because the electrons sit in 4s and 3d energy levels
which are very close - electrons are gained and lost using a similar amount of energy
when they form the ions
they also formed coloured ions in solution
Transition metals 2
, metal complexes
they have the ability to form complex ions
a complex ion is where a central transition metal is surrounded by ligands bonded by
dative covalent bonds
ligands have at least 1 lone pair of electrons where they are used to form a dative
covalent bond with the metal
ligands
monodentate (unidentate) - one lone pair of electrons
eg: H2O:, :NH3, :Cl-
bidentate - 2 lone pairs of electrons
eg: ethanedioate, ethane-1,2-diamine
multidentate - more than 1 coordinate bond
EDTA4- - can form 6 coordinate bonds with the central metal ion
complex shapes
the shape is dependent on the size of the ligands and the coordination number
coordination number is the number of coordinate bonds formed - not the number of
ligands
some ligands are small - H2O:, :NH3 (you can fit 6 around a metal ion)
some ligands are larger and you can only fit 4 - :Cl-
Transition metals 3
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