Chapter 24: Transition Elements Flashcards
What are the d-block elements?
- The elements located between groups 2 and 3 in the periodic table
Which d-block elements’ electronic configuration does not fit the trend?
- 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 molecule or ion 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
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
- Bidentate: a ligand that can donate 2 electron pairs to a central metal ion
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
What causes a 4-coordinate complex ion to have cis-trans isomerism?
- It has to be square planar
- There are 2 pairs of identical ligands
In square planar complex ions with cis-trans isomerism, which would be the cis isomer and which would be the trans isomer? Include the bond angles.
- If 2 of the identical ligands are adjacent to each other, this would be the cis isomer
- 90°
- If the 2 identical ligands are opposite each other (across the metal ion from each other, not adjacent)
- 180°
What causes a 6-coordinate complex ion to have cis-trans isomerism?
- There are 2 identical monodentate ligands, and 4 monodentate ligands of another type
- There are 2 identical monodentate ligands, and 2 bidentate ligands
In octahedral complex ions with monodentate ligands that display cis-trans isomerism, which would be the cis isomer and which would be the trans isomer? Include the bond angles.
- The trans isomer would be where the 2 identical ligands are opposite (2 other monodentate ligands separate them)
- 180°
- The cis isomer would be where the 2 identical ligands are either adjacent or one monodentate ligand apart
- 90°
Which complex ions can display optical isomerism?
- Octahedral ions with 2 or more bidentate ligands
- However, only the cis isomers display optical isomerism if there are 2 bidentate ligands (trans isomers’ mirror image would be the same)
How is cis-trans isomerism in complex ions applied in real life? Give the name and formula of the complex ion.
- Cis-platin is an anti-cancer drug
- Pt (NH3)2 (Cl)2
How does cis-platin work?
- It binds to DNA inside the cell and stops it from replicating
