Transition Metals Flashcards
Transition metals forming positive ions
4s Electrons are lost before the electrons occupying 3d orbitals
What kind of d orbitals have a special stability
Half filled or fully filled
Transition metals are defined as
Metals with incomplete d sub shell in at least one of their ions
Aufbau principle
states that in the ground state of an atom or ion, electrons fill subshells of the lowest available energy, then they fill subshells of higher energy.
What are the excpetions to the aufbau principle?
Chromium and Copper atoms, where the added stability of the half filled/ completely filled d orbitals results in 4s being half filled
An element has a particular oxidation state when
It had a specific oxidation number
Ligands
Negative ions or molecules with non bonding pairs of electrons which they donate to the central metal atom/ion forming DATIVE COVALENT BOND
Ligands can be
Mono-dentate- Donates one pair of electrons to form a dative covalent bond
Bidentate- Donates two pairs of electrons
all the way up to hexadentate
Coordination number
The total number of bonds from the ligands to the central transitional metal atom/ion
When are d orbitals no longer degenerate?
In a transition metal complex
Transition metal complex
Consists of a central metal ion surrounded by ligands
Why does
Splitting of d orbitals to higher and lower energies occur
When the electrons present in the approaching ligands cause the electrons in the orbitals lying along the axes to be repelled
What are
Strong field ligands
Ligands that cause a large difference in energy between subsets of d orbitals
When is
Light absorbed in a transtion metal complex
When electrons in a lower energy d oribtal are promoted to higher energy d orbital
Dative covalent bond
One atom provides both electrons of the bonding pair, same as any other covalent bond
Oxidation number determines
if oxidation or reduction has occurred
Rules for assigining oxidation number
- OXN of an uncombined element is 0
– Ions of single atoms have same OXN as their charge - Sum of all OXN in molecule has to be 0
– Sum of all OXN numbers on a polyatomic ion is equal to charge on the ion.
Why may transition metals have different colours
Differing oxidation states
Copper and iron when naming negative complexes
Cuprate and ferrate, everything else add an Ate to the end
common ligands with a 2- charge
Oxido 0 2-, Oxalato O4C2 2-
Blue light is absorbed
Red and green are transmitted, with a yellow colour complex.
The colour being observed is the
Complementary colour to the colour of wave length thats absorbed
why will colours of the same transition metal be different ?
When different ligands are attached to the t metal, energy absorbed will change, resulting in different wavelengths of light being transmitted. Ligands produce different crystal field splittings.
Ligand field strength is due to iys
Place in the spectrochemical series.
Why are transition metals able to absorb light
The 5 d orbitals split in term of energy, they are no longer degenerate, due to electron repulsion when the ligands attach to t metal. When electrons are promoted to the higher energy level d orbitals light is absorbed.
Spectrochemical series decreasing
Weaker field
Smaller energy difference
Longer wavelength absorbed
how
Ultraviolet radiation absorbed
appears
Will appear colourless, our eyes are unable to detect the UV radiation thats been removed from the transmitted light.
Complexes that absorb ultraviolet radiation
Will have strong field ligans, which cause a greater energy gap and will require higher energy for d-d transitions.
Why would zinc not produce coloured compounds?
Zinc does not hace incomplete d orbitals in its io, so no d-d trantions can take place as all orbitals are full.
Transition metals as
Catalysts
Transition metals and their complexes can be catalysts.
-You can have heterogeneous(same Phase as reactanats)
-or heterogenous (diff phase)
How can
Heterogenous catalysts be explained
Adsorption of the reactive molecules onto the active sites allows reaction to be catalysed.
The presence of empty d orbitals/unpaired electrons is thought to allow this.
Lowering activation energies
How can
Homogenous catalysts be explained
They can form intermediate complexes with the reactive molecules resulting in a change in oxidation state
Three main characteristics of a transition metal
- Produces ions of differing oxidation states
- Produce coloured componds
- They can act as catalysts
