13.2.1 List the characteristic properties of transition elements
- also called d-block elements
- they have partially filled orbitals as their final valence electron
- these d-block electrons and related configuration are responsible for characteristic properties
- they have variable oxidation numbers, complex ion formation, existence of coloured compounds, ability to be reducing agents, and catalytic properties
13.2.2 Explain why Sc and Zn are not considered to be transition elements
- Scandium is not a transition element because it can have ONLY a +3 oxidation number
- it loses its 2 electrons in the 4s orbital, but having only 1 electron in the 3d sub-level is too unstable so a third electron is oxidized
- however, transition metals are defined as possessing partially filled d orbitals and Sc has no d electrons at all
- Zinc is not a transition metal because it contains a full d sub-level in all its oxidation states
13.2.3 Explain the existence of variable oxidation number in ions of transition elements
Common Oxidation Numbers:
- oxidation number: the apparent net electric charge an atom would have in a covalent bond if electron pairs in covalent bonds "belonged" entirely to the more electronegative atom
- transition metals have variable ox. numbers because stable ions tend to have full, empty, or half-full sub-levels
- the metals will lose the two 4s electrons first, therefore all transition metals can form 2+ ions
- because they all will have empty 4s orbitals if they lose 2 electrons, this is a "stable" ion (one that will exist without gaining or losing more electron for a comparatively long period of time)
- another stable ion can be formed when the d orbitals lose one or more electrons to form half-full d orbitals
Common Oxidation Numbers:
- Cr: +3, +6
- Mn: +4, +7
- Fe: +3
- Cu: +1
13.2.4 Define the term ligand
- ligand: a molecule or ion surrounding a central metal atom
- it can donate a pair (or pairs) of non-bonding electron to form a dative covalent bond
- donates one pair: unidentate/monodentate
- 1+ pairs: multidentate
- common ligands: H2O, NH3, CN-, Cl-
13.2.5 Describe the explain the formation of complexes of d-block elements
- d-block metals and large p-block metals (eg. lead) have unfilled d/p orbitals
- these orbitals can accept a lone pair(s) of electrons from other species and form a dative bond with the metal ion (get covalent bonds with these metal ions)
- complex ions: species where ligands are bonded to a central metal ion
- most complex ions have: 4 ligands arranged tetrahedrally (Cl- usually), or 6 ligands arranged octahedrally (H2O, NH3 usually) around the central metal
- few examples of linear complex ions with 2 ligands do exist (eg. diaminesilver)
13.2.6 Explain why some complexes of d-block elements are coloured
- all d orbitals have exactly the same energy in an isolated atom
- but if the atom/ion is surrounded by something that distorts the electron cloud then the electric field from these affects various d orbitals differently
- ligands pull/subdivide the d orbitals into 2 different energy levels on the basis of where they are located
- a quantized amount of energy from white light is absorbed
- light coming through the sample will be the complementary colour
- the amount of splitting (and hence colour) depends on the identity of the ligand (electronegativity), oxidation state of the central metal ion, identity of central ion, and number of ligands
- Zn and Sc form colourless complex ions
- for Zn2+, because the d orbitals are full, there are no spaces for electrons to be excited so no energy is absorbed
- for Sc3+, there are no electrons in the d orbitals to excite from a lower to higher d orbital
13.2.7 State examples of the catalytic action of transition metals and their compounds
- many transition elements and their compounds are very efficient catalysts
- platinum and palladium are used in catalytic converters fitted to cars
- in the human body, iron is found in haem and cobalt is found in vitamin B12
13.2.8 Outline the economic significance of catalysts in the Contact and Haber processes
- catalysts increase the rate of reaction, meaning that more yield can be produced in a shorter amount of time
- this makes the production of ammonia and sulfuric acid more efficient, thereby reducing economic cost
- in the Haber process, iron is used as a catalyst to increase ammonia yield
- in the Contact process, vanadium is used as a catalyst to increase sulfur trioxide yield