Chapter 24: Transition Elements
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What are the d-block elements?
• The elements with their highest energy electron in a d sub-shell
Which d-block elements’ electronic configuration do not fit the trend? Why?
• Chromium and copper • Both have 1 electron in their 4s sub-shell instead of 2 so that they can either have a half-full or fully filled 3d sub-shell, as this is more stable
What are the transition elements? Required.
• The d-block elements that form at least one ion with a partially filled d sub-shell • This means that scandium and zinc, for example, aren’t transition elements
Which ions do scandium and zinc form, and why?
• Sc^3+ (loses both 4s electrons and one 3d electron) • Zn^2+ (loses both 4s electrons, so all 10 3d electrons remain)
What are 3 properties of transition metals?
• The elements can each have multiple oxidation states when forming compounds • They can form coloured ions • The elements and their compounds can act as catalysts
Give 2 possible oxidation states and corresponding colours of the solutions of 2 transition metals.
• Chromium: • chromium (VI) is orange • chromium (III) is green • Iron: • iron (II) is pale green • iron (III) is pale yellow
How do transition metals act as catalysts?
• They provide an alternative reaction pathway with lower activation energy
Give an example of a transition metal acting as a catalyst.
• Nickel in the hydrogenation of alkenes
What is a complex ion?
• Complex ions are formed when one or more molecules or negatively charged ions (ligands) bond to a central metal ion
What is a ligand? Required.
• A species with a lone pair of electrons that it donates to a central metal ion to form a dative covalent/ coordinate bond
What is the coordination number?
• The number of coordinate bonds attached to the central metal ion
How are the formulae of complex ions written? Give an example.
• There are square brackets surrounding the complex ion, with the overall charge written on the outside • Inside the square brackets the metal ion is written first, but without its charge • The ligand(s) come next: • if its a molecule, its written inside regular brackets, followed by the number of times it is present in the complex ion • if it is a single element (such as a chloride ion) it is written without brackets and its charge • [Cr(H2O)6]3+
How can the charge on the central metal ion be found when given the charge and formula of the complex ion?
• Subtract the overall charge of the ligands from the charge of the complex ion
What do co-ordination numbers determine?
• The shape of the complex ion
What shape does a coordination number of 6 lead to? What is the bond angle?
• Octahedral • 90°
What shape does a coordination number of 4 usually lead to? What is the bond angle? What condition leads to an exception?
• Tetrahedral • 109.5° • If the transition metal ion has 8d electrons
What is the alternative shape a coordination number of 4 can cause? What is the bond angle? Give 3 examples of ions that cause this.
• Square planar • 90° • Platinum (II), palladium (II) and gold (III)
How are complex ions with a square planar shape drawn?
• The ligands are arranged as if in the corners of a rectangle • The top 2 have dashed wedges • The bottom 2 have plain wedges
What do all drawings of complex ions need to show?
• The metal ion needs to be bonded to the atom with the lone pair (draw these in first) • The overall charge
What 2 categories can ligands come under, and what does each mean?
• Monodentate: a ligand that can donate one pair of electrons to a central metal ion to form one coordinate bond with it • Bidentate: a ligand that can donate 2 electron pairs to a central metal ion to form 2 coordinate bonds with it
What are the 2 most common bidentate ligands?
• 1,2-diaminoethane/ ‘en’ • (CH2NH2)2 • Ethanedioate ion • (COO-)2
How are complex ions with bidentate ligands drawn?
• You draw the central metal ion and the bonds around it in the regular way • Each bidentate ligand makes 2 adjacent coordinate bonds with the central metal ion
What types of stereoisomerism can complex ions display?
• Cis-trans isomerism • Optical isomerism
Complex ions with what coordination number can display cis-trans isomerism?
• 4 • 6