Atomic Properties of Transition Metals

Atomic Radius

The atomic radius of main group elements generally decreases from left to right across a period and increases down a group. Transition metals follow similar trends, but changes in size are less pronounced due to electron configuration effects.

• Across a period: Number of outermost electrons (n) is constant; atomic radius decreases due to increased effective nuclear charge.

• Down a group: Atomic radius increases, but for 5d transition metals, the increase is less than expected due to lanthanide contraction.

• Lanthanide Contraction: The decrease in atomic radius for 5d elements is caused by poor shielding of 4f electrons, resulting in a higher effective nuclear charge.

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

Additional info: Lanthanide contraction is a key concept in understanding the periodic trends of transition metals.

Density of Transition Metals

Density Trends

Density increases as the atomic mass of the metal increases. The increase in density down a group is more significant than across a period.

• Density is affected by both atomic mass and atomic radius.

• Transition metals in the same period have similar densities, but those in lower periods (higher atomic number) are denser.

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

Transition Metals: Location and Electron Configurations

Periodic Table Position

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.

• Electron configuration for Ti (Z = 22):

• Electron configuration for Ti2+:

Example: Provide condensed electron configuration for V3+ ion.

Exceptions in Electron Configurations

Chromium and Copper Exceptions

Starting from chromium (Z = 24), exceptions to the expected electron configurations occur due to stability of half-filled and fully-filled d subshells.

• Chromium: (instead of )

• Copper: (instead of )

• These exceptions arise because half-filled and fully-filled d orbitals are energetically favorable.

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

Additional Exceptions (Period 5)

Further exceptions are observed in Period 5, such as for Nb (Z = 41) and Ru (Z = 44).

• Nb:

• Ru:

Example: Provide condensed electron configuration for Ru atom.

Magnetism: Paramagnetic vs. Diamagnetic

Electron Pairing and Magnetism

An orbital can hold a maximum of 2 electrons with opposite spins. Magnetism depends on the presence of unpaired electrons:

• Paramagnetic: Atoms/ions with at least one unpaired electron; attracted to magnetic fields.

• Diamagnetic: All electrons are paired; repelled by magnetic fields.

Example: Determine if vanadium atom is paramagnetic or diamagnetic.

Additional info: Most transition metal ions are paramagnetic due to unpaired d electrons.

Ligands in Coordination Chemistry

Ligand Types

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

Example: Which of the following is a neutral ligand? Bromide, Hydrogen sulfide, Ammonium, Hydroxide, Cyanide.

Ligand Reaction and Adduct Formation

The adduct is the product of a Lewis base and acid reaction. The overall charge of the adduct equals the sum of the metal cation and ligand charges.

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

Complex Ion Formation

Complex Ions

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

Example: Provide the complex ion structure for Ti4+ with 6 CO molecules: [Ti(CO)6]4+

Coordination Complexes

Coordination Complex Structure

Ionic compounds composed of a complex ion and a counterion maintain neutrality. The ionic compound is written as:

Example: Determine the formula for the coordination complex created between [Cr(CN)6](OH)3- and F-.

Ligand Classification

Monodentate, Bidentate, and Polydentate Ligands

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)

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

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

Key Equations and Concepts

• Effective Nuclear Charge: (where S is the shielding constant)

• Electron Configuration Notation:

• Complex Ion Formula:

Additional info: Understanding electron configurations and ligand types is essential for predicting properties and reactivity of transition metal complexes.