Transition Elements and Complex Ions Practice Flashcards

A set of vocabulary-style flashcards covering transition metal chemistry, including properties, electron configurations, complex ion reactions, d-orbital splitting, and redox equations.

Transition element

A d-block element that can form one or more stable ions with an incomplete d-subshell.

Electron configuration of Chromium (Cr)

$$1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^1$$

Electron configuration of Copper (Cu)

$$1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^1$$

Melting points of transition metals

Higher than typical s-block metals like calcium because extra $3d$ electrons increase metallic bonding strength, requiring more energy to overcome bonds.

Densities of transition metals

Greater than s-block metals because nuclear charge increases across the period with constant shielding, decreasing atomic radius and allowing closer packing.

Catalytic properties of transition elements

Used as catalysts because they are stable in variable oxidation states, allowing them to easily give or take electrons to or from other molecules.

Reason for variable oxidation states

Electrons in the $4s$ and $3d$ orbitals have very similar energies, so similar amounts of energy are required to gain or lose different numbers of electrons.

Maximum oxidation state prediction

Calculated as: maximum oxidation state = number of $4s$ electrons + number of unpaired $3d$ electrons (copper is an exception).

Ligand

A species that has a lone pair of electrons that forms a dative covalent bond with a central metal atom or ion.

Monodentate, Bidentate, and Polydentate

Monodentate forms $1$ coordinate bond; Bidentate forms $2$ coordinate bonds; Polydentate forms more than $2$ coordinate bonds.

Complex ion

A molecule containing a central metal ion surrounded by one or more ligands bonded by coordinate bonds.

Ligand substitution

A reaction in which one ligand in a complex ion is replaced by another.

Formation of hexaaquacopper(II)

When a copper(II) compound dissolves, water molecules form dative covalent bonds with the metal ion: $Cu^{2+} + 6H_2O ightarrow [Cu(H_2O)_6]^{2+}$.

Reaction of [Cu(H2O)6]2+ with ammonia

$[Cu(H_2O)_6]^{2+} + 4NH_3 ightleftharpoons [Cu(NH_3)_4(H_2O)_2]^{2+} + 4H_2O$. A pale blue solution transitions to a dark blue solution (initially forming a pale blue precipitate $Cu(OH)_2$).

Distorted octahedral shape

The shape of $[Cu(NH_3)_4(H_2O)_2]^{2+}$, caused by $Cu ext{-} O$ bonds being longer than the $Cu ext{-} N$ bonds.

Reaction of [Cu(H2O)6]2+ with chloride ions

$[Cu(H_2O)_6]^{2+} + 4Cl^- ightleftharpoons [CuCl_4]^{2-} + 6H_2O$. Pale blue solution changes to a yellow solution.

Shape of [CuCl4]2-

Tetrahedral; this shape occurs because $Cl^-$ ions are larger and have stronger repulsion than water ligands, allowing only $4$ to surround the ion.

Reaction of hexaaquacopper(II) with hydroxide ions

$[Cu(H_2O)_6]^{2+} + 2OH^- ightarrow [Cu(H_2O)_4(OH)_2] + 2H_2O$; shifts from a blue solution to a blue precipitate.

Reaction of [Co(H2O)6]2+ with 4Cl-

$[Co(H_2O)_6]^{2+} + 4Cl^- ightarrow [CoCl_4]^{2-} + 6H_2O$; shifts from a pink solution to a blue solution.

Coordination number

The number of coordinate bonds formed between the ligands and the central metal ion or atom.

Shapes for coordination number 4

Tetrahedral (bond angle $109.5^ ext{o}$) or square planar (bond angle $90^ ext{o}$).

Redox equation: MnO4- and Fe2+ salt

$$MnO_4^- + 8H^+ + 5Fe^{2+} ightarrow Mn^{2+} + 5Fe^{3+} + 4H_2O$$

Reduction half equation: Cr2O7 2- to Cr3+

$$Cr_2O_7^{2-} + 14H^+ + 6e^- ightarrow 2Cr^{3+} + 7H_2O$$

Predicting oxidation and reduction (Eθ)

The half-cell with the more positive $E^{ heta}$ is reduced, and the half-cell with the more negative $E^{ heta}$ is oxidised.

Conditions for feasibility spontaneity

A reaction may be feasible using standard electrode potentials but not occur spontaneously due to non-standard conditions or if ambient energy is lower than the activation energy.

d-orbital splitting in octahedral complexes

Ligand electrons repel metal d-orbital electrons, splitting them into two groups: two higher energy orbitals and three lower energy orbitals.

d-orbital splitting in tetrahedral complexes

Split into two higher energy orbitals (containing three d-orbitals) and a lower energy group (containing two d-orbitals); the opposite of octahedral splitting.

Transition metal ion color origin

White light passes through; energy is absorbed to promote an electron between split d-orbitals. The observed color is the complementary color to the wavelength absorbed.

Factors affecting complex color

The nature of the ligand, the oxidation state of the metal, and the coordination number of the transition metal ion.

Cisplatin function

An anti-cancer drug that binds to DNA, preventing cell replication and leading to apoptosis (cell death).

Stability Constant (Kstab)

The equilibrium constant for the formation of a complex ion from its constituent molecules or ions in a solvent.

Significance of a large Kstab

The larger the stability constant, the greater the stability of the complex ion; indicates which reaction is prioritized in competing equilibria.