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 with notable exceptions due to electron configurations and subshell filling.

• Across a period: The number of outermost electrons increases, but the atomic radius remains relatively constant for transition metals due to poor shielding by d-electrons.

• Down a group: Atomic radius increases, but 5d transition metals are similar in size to 4d metals due to the lanthanide contraction.

Example: Predict which element from each pair has the largest atomic size:

• Ni vs Ti

• Tc vs Ru

• Rh vs Nb

• Y vs Ag

Lanthanide Contraction

The lanthanide contraction refers to the decrease in atomic and ionic radii of the elements in the lanthanide series, which affects the size of 5d transition metals. This is due to poor shielding by 4f electrons, resulting in a higher effective nuclear charge.

Additional info: The lanthanide contraction causes 5d elements to be similar in size to 4d elements, despite being in a higher period.

Density

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

• Density is affected by atomic mass and atomic radius.

• Transition metals in the same group show a marked increase in density down the group.

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

Electron Configuration of Transition Metals

General Electron Configuration

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, typically the s orbital before the d orbital.

• Example: Titanium (Ti)

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

Practice Problems

• Write electron configuration for ion of Tungsten (IV).

• Determine electron configuration for Cd2+ in CdS.

Exceptions to Electron Configuration

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

• Chromium (Cr): (instead of )

• Copper (Cu): (instead of )

Additional info: These exceptions are due to increased stability of half-filled () and fully-filled () subshells.

Period 5 and 6 Exceptions

Additional exceptions are observed in Period 5 and 6 transition metals, especially in the filling of 4d and 5d orbitals.

• Niobium (Nb):

• Ruthenium (Ru):

Magnetism in Transition Metals

Paramagnetic vs. Diamagnetic

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

• Paramagnetic: Atoms or 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.

Practice Problems

• Which atom has the most unpaired electrons: Co, Mn, Ti, Zn, Fe?

• Write electron configuration for Ni(III) ion and state if it is paramagnetic or diamagnetic.

Coordination Chemistry

Ligand Types

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

Example: Which of the following is a neutral ligand?

Ligand Reaction and Adduct Formation

Adduct formation is a type of Lewis acid-base reaction where a metal cation (Lewis acid) reacts with ligands (Lewis bases) to form a complex.

• Overall charge of adduct = sum of metal cation and ligand charges.

Example: Determine the adduct product when 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 for Ti4+ with 6 CO molecules.

Coordination Complexes

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

• Coordination Complex I: [Ni(NH3)4]Cl2

• Coordination Complex II: Li2[TiBr4]

Example: Determine the formula for the coordination complex created between [Cr(CN)6](OH)2- 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

• Bidentate: Two donor atoms

• Polydentate: More than two donor atoms

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

Practice and Application

• Write electron configurations for various transition metal ions.

• Determine paramagnetic or diamagnetic nature of ions.

• Identify ligand types and classify them.

• Write formulas for coordination complexes and determine their charges.

Additional info: These topics are foundational for understanding transition metal chemistry, coordination compounds, and their properties in General Chemistry.