Transition Metals

—> used in a variety of chemical processes.

—> have an incomplete d sub shell as a stable ion.

—> form coloured compounds e.g. copper sulphate is blue.

—> as you go across period 4, Sc to Zn - the 3d subshell is being filled

—> the 4s subshell is filled before 3d (Cu & Cr are an exception)

—> 4s and 3d overlap as a result of this

—> when they react, they lose electrons to form a positive ions

—> they lose electron from the 4s subshell FIRST, then the 3d

—> this allows them to form ions with multiple oxidation states

—> all form a 2+ ion

—> transition metal compounds form complex ions.

—> complex ions consists of a central metal ion surrounded by ligands.

—> Ligands : a molecule/ion that donates a pair of electrons to the central transition metal ions from a dative covalent bond.

—> other complex ions include [Cu(H2O)6]2+

—> are used as industrial catalysts.

—> Catalysts : a substance that speeds up a reaction. Can take part in the reaction but is left uncharged at the end of the reaction.

—> platinum and rhodium - used in catalytic converts in cars

• convert the CO and NO emissions into CO2 and N2 (none polluting)

—> Manganese dioxide : acts as a catalyst in the decomposition in of hydrogen peroxide into water and oxygen

• uses vandium oxide to produce sulphuric acid
• consists of 4 stages

In stage 2 : the vanadium(V) oxide catalyst takes part in the reaction and is changed in the reaction but remains chemically unchanged by the end of the reaction.

• doesn’t get used up
• can constantly be used

—> Iron is used as the catalyst in the Haver process for the synthesis of ammonia. Nitrogen reacts with hydrogen to produce ammonia.

N2 (g) + 3H2 (g) -><- 2NH3 (g) 

—> the iron catalysts speeds up the reaction by lowering the activation energy so that the N2 bonds and H2 bonds can be broken more readily.

—> in order for a reaction to take place, particles must collide with AT LEAST the activation energy in order for products to form.

—> catalysts reduce the amount of energy needed by the particles to form a product.

—> Activation energy : the minimum amount of energy needed by the reactants for collisions to result in a reaction taking place.

—> speeds up a reaction

—> provides an alternative route with a lower activation energy

—> have variable oxidation states - can gain/lose electrons

—> returns to original oxidation state at the end of the reaction

—> provide a surface for the reaction to take place on

—> Homogenous

• catalysts is in the same physical state as the reactant
• E.g. ozone depletion
• catalysts AND reactants are gases

—> Heterogenous

• catalysts is in a different physical state from the reactants
• E.g. haber process
• catalyst (Fe) is a solid but the reactants N2 and H2 are gases

—> reactants adsorbed onto the surface of the catalyst = adsorption

—> the bonds within the reactants weaken and break

—> new bonds form and products desorbed away. They are desorbed = desorption