week 8 Flashcards
group 6 elements (25 cards)
Atomic radius (gorup 6)
increase in atomic radius down the group from Cr to Mo but the radii of Mo and W are the same.
DUE to lanthanoid contraction
Ionisation energy g6
First ionisation energy increases down a group is due to the combination of an increase on eff with a similar metallic radius
subsequent removal of electrons from the 2nd and 3rd row transition metals becomes easier due to shielding by the innermost electrons. This leads to a much more gradual increase in the second and subsequent ionisation energies.
Chromium
The ground state configuration
The ground state configuration 4s1 3d5 .
Chromium oxidation sates
- H2CrO4 acts as an acid as it reacts with the OH- anions to produce CrO42- (yellow) and water (condensation reaction).
The product CrO42- reacts under acidic conditions to produce the dichromate Cr2O72- (orange) and water (condensation reaction).
chromium also exists in low oxidation states
- Cr0 and Cr2+. They are strong reducing agents and easily oxidise to Cr3+. Figure 6 shows the colour difference of Cr2+(blue) and Cr3+(green).
Coordination Complexes
WHAT + WHAT BOND
A coordination complex consists of a central cation (metal ion) bonded to molecules or anions (called ligands)
The bond formed is known as a coordinate bond, a donor covalent bond or a dative bond.
CORDINATION COMPLEXES WHY?
Metal ions do not exist as isolated ions – they are surround by other molecules/anions.
Coordination complexes form because the positive metal ion is a Lewis acid (an electron pair acceptor) and the ligands surrounding it are Lewis bases (electron pair donors).
COUNTER IONS WHY?
may be present to maintain charge balance in a coordination compound
how to draw complexes
central metal ion
draw with square brackets
ligands+ bonds dashed straight and thick.
any overall charge
counter ion and optential hydrate with dot in-between
What is a coordinate bond?
a covalent bond between a Lewis acidic metal ion and a Lewis basic ligand in which both electrons originate from the ligand
What is a coordination number?
the number of donor atoms coordinated to a metal ion
What is a counter ion?
an ion that balances the charge on a cationic or anionic complex ion
What is a donor atom?
an atom of a ligand in a complex that is directly coordinated to the transition metal ion
What is a Lewis acid?
an electron-pair acceptor
What is a Lewis base?
an electron-pair donator
What is a ligand?
a molecule or an anion that can coordinate to a transition metal ion to form a complex
What is a octahedral conformation?
describes a molecule in which a central atom is surrounded by six atoms located at the vertices of an imaginary octahedron
What is a square planar conformation?
a geometry adopted by 4-coordinate complexes in which the four M-L bonds point to the corners of a square
What is a tetrahedral conformation?
a geometry adopted by 4-coordinated complexes in which the central metal ion is coordinated to four ligand donor atoms located at the corners of an imaginary tetrahedron
What is the oxidation state of metals in their elemental form?
0
Why do coordination complexes form?
The positive metal ion is a Lewis acid (an electron pair acceptor) and the ligands surrounding it are Lewis bases (electron pair donors)
What type of bond forms between the metal and the ligands?
Cooridnate bond/donor covalent bond/dative bond
What does a coordination compound consist of?
The metal complex and counterions
True or False: A coordination compound may dissociate into anions and cations in solution
True
