transition elements

• Transition elements are found in the d-block of the periodic table and form one or more stable ions with incomplete d orbitals
• The d subshell can hold up to 10 electrons
• Scandium and zinc are in the d block but not transition elements because their ions do not have an incomplete d subshell
• Scandium forms one stable ion, Sc3+, with an empty d subshell
• Zinc forms one stable ion, Zn2+, with a full d subshell
• Transition elements have higher melting points and densities compared to s-block metals due to extra 3d electrons and smaller atomic sizes
• Transition metals can exist in variable oxidation states due to similar energies of 4s and 3d orbitals
• Transition elements and their complexes function as catalysts due to variable stable oxidation states and vacant d orbitals that can form dative bonds with ligands
• Transition elements form colored compounds because of the way the partially filled d orbitals split to different energies
• Transition metal ions react with monodentate water ligands to form complexes, like Cu2+ + 6H2O → [Cu(H2O)6]2+ (blue solution formed)
• Metal aqua ions react with aqueous ammonia to form precipitates, like Cu2+ + 2NH3 → [Cu(H2O)4(OH)2] + 2NH4+ (blue solution turns to light blue precipitate)
• Chloride ions act as monodentate ligands when they react with metal aqua ions, with only four Cl- ions fitting around the metal ion due to their charge and size
• When chloride ions react with metal aqua ions, they act as monodentate ligands, reducing the coordination number from 6 to 4
• In a linear complex, a silver metal ion forms two coordinate bonds with bond angles of 180°
• An octahedral complex is formed when a metal ion has 6 coordinate bonds, with bond angles of 90°
• A tetrahedral complex is formed when there are four coordinate bonds, with bond angles of 109.5°
• Square planar complexes occur when there are four coordinate bonds instead of a tetrahedral shape, with a bond angle of 90°; an example is cisplatin, an anti-cancer drug
• Ligand exchange, or ligand substitution, occurs when ligands swap places with one another, maintaining the coordination number and shape if the ligands are similar in size and charge
• Potassium manganate(VII) and potassium dichromate(VI) are commonly used as oxidizing agents in redox titrations
• Acidic conditions are required for both oxidizing agents to work, with dilute sulfuric acid being chosen for its effectiveness
• The redox potential of an ion indicates how easily it can be reduced to a lower oxidation state; the smaller the redox potential, the more stable the ion is and the less likely it will be reduced
• Degenerate orbitals in metal ions split when ligands join, causing the energy levels of the d orbitals to split due to repulsion from the ligands' electric fields
• In an isolated metal atom or ion, the five d orbitals are degenerate because they all have the same energy level
• When ligands join to a metal ion, the electric fields of the ligands repel the d orbitals, causing the energy levels of the d orbitals to split
• In a tetrahedral complex, none of the orbitals point directly to the ligands, so the splitting energy is less than that of octahedral complexes
• Visible light hitting a transition metal ion causes electrons to be excited to higher energy levels, resulting in absorption of certain frequencies of light and the transmission or reflection of the rest, leading to the color of the complex seen
• Different ligands in metal complexes cause different amounts of visible light to be absorbed, resulting in different colors being observed
• Octahedral complexes with two monodentate ligands of one type and four monodentate ligands of another type exhibit cis-trans isomerism
• Optical isomerism occurs in octahedral complexes with three bidentate ligands, resulting in two non-superimposable mirror image forms
• Cisplatin, a complex of platinum(II), is used as an anticancer drug by binding to DNA, causing kinks in the DNA helix and preventing proper cell replication
• Cisplatin can bind to DNA in healthy cells, causing issues like hair loss, immune system suppression, and kidney damage
• Stability constants, Kstab, determine the most stable complex in competing equilibria in ligand exchange reactions
• The larger the value of Kstab, the more stable the complex ion formed, and the further right of the equilibrium the reaction lies