Transition Metals: Periodic Trends, Electron Configurations, and Coordination Chemistry

Atomic Radius of Transition Metals

The atomic radius is a measure of the size of an atom, typically the distance from the nucleus to the outermost electron shell. For transition metals, trends in atomic radius are influenced by their position in the periodic table.

• Across a period: Atomic radius generally decreases from left to right due to increasing nuclear charge, which pulls electrons closer to the nucleus.

• Down a group: Atomic radius increases as additional electron shells are added, but the increase is less pronounced for transition metals due to the lanthanide contraction.

• Lanthanide Contraction: The gradual decrease in the size of the atoms and ions of the lanthanide series elements, which affects the atomic radii of subsequent elements.

Example: Predict which element from each pair has the largest atomic size: Ni & Ti, Tc & Ru, Rh & Nb, Y & Ag.

Density of Transition Metals

Density is defined as mass per unit volume. For transition metals, density increases as the atomic mass increases, but the trend is more significant down a group than across a period.

• Density increases as the mass of the metal increases.

• Increase in density down the group is more significant than across the period.

Example: Identify a transition metal with the highest density: Zn, Sc, Os, Hf.

Transition Metals in the Periodic Table

Transition metals occupy the d-block (Groups 3-12) of the periodic table. For cations, electrons are lost from the highest principal quantum number (n) shell first.

• Transition metals are found in the center of the periodic table (d-block).

• Electron configurations for transition metal ions are written by removing electrons from the s orbital before the d orbital.

Example: Provide a condensed electron configuration for Vanadium (III) ion, V3+.

Electron Configuration Exceptions

Some transition metals have exceptions to the expected electron configurations, especially chromium (Cr) and copper (Cu) families.

• For Cr (Z = 24): (half-filled d subshell is more stable)

• For Cu (Z = 29): (filled d subshell is more stable)

• Similar exceptions occur in higher periods (e.g., Mo, Ag, Ru).

Example: Write the condensed electron configuration for Ag+ (Z = 47).

Paramagnetic vs. Diamagnetic

Atoms and ions can be classified as paramagnetic or diamagnetic based on their electron configurations.

• Paramagnetic: Atoms with one or more unpaired electrons; attracted to a magnetic field.

• Diamagnetic: Atoms with all electrons paired; weakly repelled by a magnetic field.

Example: Determine if the vanadium atom is paramagnetic or diamagnetic.

Ligand Types

Ligands are molecules or ions that act as Lewis bases, donating at least one lone pair to a metal cation to form a coordination complex.

• Neutral ligands: e.g., H2O, NH3, CO

• Anionic ligands: e.g., Cl-, CN-, OH-

Example: Which of the following would represent a neutral ligand? (e.g., Ammonium)

Ligand Reaction and Adduct Formation

Ligands react with metal cations to form adducts (complexes) via Lewis acid-base reactions. The overall charge of the adduct is the sum of the metal cation and ligand charges.

Example: Determine the adduct product when a Ni(III) ion combines with 2 bromide ions.

Complex Ion Formation

A complex ion is an adduct with a central metal cation covalently bonded to ligands. The complex ion is always written in brackets.

Example: Provide the complex ion structure when a Ti4+ ion combines with 6 carbon monoxide molecules.

Coordination Complexes

Coordination complexes are ionic compounds composed of a complex ion and a counterion to maintain neutrality. The formula is written with the complex ion in brackets, followed by the counterion.

Example: Determine the formula for the coordination complex created between [Cr(CN)6](OH)24- and F-.

Ligand Classification

Ligands are classified by the number of donor atoms that can donate a lone pair to the central metal.

• Monodentate: One donor atom (e.g., Cl-, NH3)

• Bidentate: Two donor atoms (e.g., ethylenediamine, oxalate)

• Polydentate: More than two donor atoms (e.g., EDTA4-)

Example: Classify the following anionic ligands as monodentate, bidentate, or polydentate.

Key Equations and Concepts

• Electron Configuration: (for transition metals, electrons are removed from 4s before 3d when forming cations)

• Density:

• Paramagnetism: Atoms with unpaired electrons are paramagnetic.

• Coordination Number: The number of ligand donor atoms bonded to the central metal ion.

Additional info:

• Practice problems and examples are included throughout to reinforce key concepts.

• Tables have been recreated in HTML for clarity and study purposes.

• Some content has been logically inferred and expanded for completeness and academic context.