3.2.5.4 Formation of Coloured Ions
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What is colour caused by?
The compounds absorbing energy that corresponds to light in the visible region of the spectrum
What causes a purple colour?
Absorption of all light but red and blue
How are transition metals linked to colour?
The presence of a transition ion or metal in a compound or complex gives a colour
What causes a colour in transition metals?
A partially filled d subshell
How is the d subshell in transition metals split?
Two sets of orbitals Ground state and excited state which differ in energy
How does light affect the d subshell?
Energy in the visible spectrum causes electrons to jump from ground state orbitals to an excited state at a higher energy level
How does colour relate to the absorption of frequencies of light?
The complimentary colour (frequencies which are not absorbed) is observed as they are reflected or transmitted
Why do different transition ligands create different colours?
Different metal ions and different charges of the ions of the same metal and different ligands cause different splitting of the d subshell This causes different visible light frequencies being absorbed which changes the observed colour
What changes the splitting of the d subshell to change and therefore affects the colour observed?
Different ligands of the same metal ion Different charges of the ions of the same metal Different metal ions The shape of the complex The coordination number
How do you work out the energy difference in electrons between the ground state and excited state?
/\E = hv E = energy in joules h = Planck's constant (6.63 x 10(-34)) v = frequency in hertz of the light absorbed
How is a colorimeter used to detect transition metals?
It can find the ratio of metal ions to ligands in a complex This gives the formula of the complex A metal and ligand solution are mixed in different proportions When they are mixed in the correct ratio, there is the maximum concentration of complex in the solution This is when the solution will absorb the most light
What is the equation linking wavelength to frequency?
c = v x lambda ( /\ ) c = speed of light v = frequency of light in hertz Lambda = wavelength in metres