IB Chemistry III TestTransition Metals – Periodicity and Atomic Absorption

15 Jan. 2009

13.1 Trends across Period 3

13.1.1: Explanations of Compounds

Compound and DetailsNa2O MgO Al2O3 SiO2 P4O10 (P4O6) SO3 (SO2) Cl2O7 (Cl2O)

State at 25oC Solid Solid Solid Solid Solid (Solid)

Liquid (Gas) Liquid (Gas)

Explanation

Ionic bonding; lattice

Ionicbonding;

lattice

Ionic bondin

g; lattice

Covalent, but

Diamond-like

structure

Covalent, simple

molecular

Covalent, simple

molecular

Covalent, simple

molecularConductivity Good Good Good Very poor None None None

Explanation

Ionic – “sea” of electro

ns

Ionic – “sea” of electrons

Ionic – “sea”

of electro

ns

Diamond structure

allows little electron

flow

Covalent – no free

electrons

Covalent – no

free electrons

Covalent – no

free electrons

13.1.2 Reactions of Chlorine and Chlorides in Water

Chlorine – Forms acidic HCLCl2O7 – Forms acidic HCLO4

NaCl and MgCl2 – Dissolve EasilyChlorides of Al, Si, P, and S – Form fumes of HCL

13.2 First-row d-block elements

13.2.1 Transition Elements

Transition elements display variable oxidation numbers (such as Cu, which forms +2 and +3 cations), form complex ions, create vibrantly colored compounds, and serve as effective catalysts.

13.2.2 Sc and Zn are anomalous

Sc – 4s23d1: Only forms +3 ion (because it is most stable when losing both the s electrons and the single d electron)Zn - 4s23d10: Only forms +2 ion (because it is most stable when losing the two s electrons only, and retaining its full d orbitals)

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13.2.3 Variable Oxidation Number

All transition elements (except Sc) can show an oxidation number of +2 because of their two 4s electrons, which are easily removed. The d and s orbitals are of very close energy level, so many elements lose d electrons almost as easily as s electrons. Common variations:

V: +2, +4, +5Cr: +2, +3, +6Mn: +2, +4, +7

Fe: +2, +3Cu: +1, +2, +3

13.2.4 Ligands

Ligand: atom or ion or molecule that bonds with a metal cation to form a complex ion. Ligands can be anions, or neutral (like

NH3 or H2O), but must contain a non-bonding pair of electrons.

13.2.5 Formation of d-block complexes

To form a complex ion, the ligand creates an electrostatic field around the metal ion that splits the d orbital into two separate energy levels. They absorb energy in either large or small amounts.

Example formation: [Fe(H2O)6]+3.

Small ∆o: Electrons require little energy to move to a higher-level d orbital, and thus split into a diamagnetic state.

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Large ∆o: It would require more energy to split to a higher level than to pair electrons in lower energies, so the complex becomes paramagnetic.

13.2.6 Cause of color

When the d orbitals of a metal split due to a ligand’s electrostatic field, those in the lower level can absorb energy. Depending on the extent of that absorption, different wavelengths of visible light are absorbed. Depending on how much energy is absorbed, varied frequencies of light will also be absorbed by the electrons, resulting in a color formed by the remaining, reflected light.

Remember that wavelength is inversely proportional to frequency (high wav = low freq)

When a primary color (R, G, B) is removed, the combination of the remaining two is seen. (eg: Red is absorbed, so G+B= Cyan

is left.) When a secondary color (Yellow, Cyan, Magenta) is removed, the

non-involved primary color is seen. (eg: Yellow is absorbed. This means that R+G are gone—so blue is seen.)

Wavelength Table:700 nm – Red

Orange – 600 nmYellow – 570 nm

510 nm – Green475 nm – Blue

Although the internet says 475 for blue and 510 for green, if they tell you 500, assume blue. It’s more common. Anything higher than about 530 is probably green.

13.2.7 Examples of Catalytic Action

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Heterogeneous: Solid catalyst, non-solid reagents1. Breakdown of hydrogen peroxide: H2O2 –MnO2 2H2O + O2

2. Contact Process: SO2 + O2 –V2O5 2SO3 3. Haber Process: 3H2 + N2 –Fe 2NH3

4. Hydrogenation: C2H4 + H2 –Ni C2H6

5. Catalytic Converters using Pd, Pt, and Rh.

Homogeneous: Catalyst in same state as reagentsEsterificaton: Carboxylic acid + alcohol –H + Ester

13.2.8 Economics

The metal catalysts in Contact and Haber Processes are very useful from an economic standpoint: they increase the speed and decrease the activation energies of reactions, requiring less time and less input to create more output. This makes the reactions more efficient, which means they are more cost-effective.

Atomic Absorption

A.8.1. Spectrochemical seriesLigand ability to split orbitals.

I- < Br- < Cl- < OH- < H2O < NH3 < CN-

High-spin----low spin

Least splitting-----most splitting

A.8.2Different metal ions produce different colors.Oxidation # determines the # of electrons that can change energy levels by absorbing light—if there are no electrons to absorb energy, or all the levels are filled, then no light will be absorbed.Ligand determines splitting and spin: a low-spin molecule needs a lot of energy to excite to a higher level—which means it’ll absorb a lower wavelength of light.Energy absorption determines color change (whatever is not absorbed is left behind as colored light)

High-wavelength light (red, 700 nm) low-E absorptionLow-wavelength light (blue, 500 nm) high-E absorption

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A.8.3

Organic models containing a double bond absorb more UV and visible radiation because of pi electrons, which are free to excite to higher levels and move around more.

A.8.4 and A.8.5

UV spectroscopy is used only to detect pi (double and triple) bonds. That’s all.

The more bonds present, (eg. 1 double bond, 5 double bonds, ten…), the lower-energy (higher wavelength) light can be absorbed. Since UV light is of higher energy, this means that molecules with more double bonds will absorb less UV and more visible.

Conjugated bonds (alternating between double and single) absorb UV easily.

A.8.6

Absorbance and Concentration are directly related. Everything else in the formula is a constant.

Good luck!

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