Overview
This lecture introduces d-block (transition) elements, discussing their position in the periodic table, defining characteristics, electronic configuration, physical and chemical properties, and variable oxidation states.
Position and Definition of D-block Elements
- D-block elements are also called transition elements and occupy groups 3 to 11 in the periodic table.
- They are positioned between the s-block (left) and p-block (right) elements.
- Transition elements have atoms with partially filled d subshells or form ions with partially filled d subshells.
- Group 12 elements (Zn, Cd, Hg) are generally not considered transition elements due to fully filled d subshells in their common oxidation states.
Electronic Configuration and Series
- D-block elements in period 4: Scandium (Sc) to Copper (Cu), filling 3d orbitals.
- Period 5 and 6 d-block elements fill 4d and 5d orbitals, respectively.
- The characteristic electronic configuration is (n-1)d¹⁻¹⁰ ns¹⁻².
- After lanthanum (La) and actinium (Ac), f-block (inner transition) elements fill 4f and 5f subshells.
Physical and Chemical Properties
- Transition metals are typically hard, have metallic luster, and high melting and boiling points.
- They are good conductors of heat and electricity and often form alloys.
- Many transition metals are found as ores and minerals; e.g., iron is present in hemoglobin and myoglobin.
- Metals like Fe, Ni, Cu, etc., are often used industrially and biologically.
Oxidation States and Reactivity
- Transition elements commonly exhibit variable oxidation states (e.g., Fe²⁺ and Fe³⁺).
- Removal of electrons generally occurs from the outer s and then d orbitals.
- The most stable oxidation states correspond to half-filled or fully filled d subshells.
- Unusual high oxidation states are possible but less common.
- Chemical reactivity trends (e.g., with acids) and ion formation are important for their chemistry.
Bonding and Melting Points
- Metallic bonding in transition metals involves delocalized d electrons, increasing bond strength and cohesion.
- Elements with completely filled d subshells (e.g., Zn, Cd, Hg) have lower melting/boiling points and weaker metallic bonding.
- Melting points generally peak in the middle of the transition series, with minima at fully filled d subshells.
- Tungsten (W) has a very high melting point and is used in light bulb filaments.
Key Terms & Definitions
- Transition Elements — Elements whose atoms or ions have partially filled d subshells.
- D-block — Section of the periodic table where d orbitals are being filled (groups 3-11).
- Penultimate Shell — The shell just inside the outermost shell, where d electrons are added.
- Electronic Configuration — The arrangement of electrons in atomic orbitals.
- Oxidation State — The charge of an atom after losing or gaining electrons.
- Alloys — Mixtures of metals with enhanced properties.
- Metallic Bonding — Bonding due to delocalized electrons within metals.
- Lanthanides/Actinides — Inner transition elements filling f orbitals.
Action Items / Next Steps
- Review electronic configurations for transition elements and practice assigning them.
- Understand trends in physical and chemical properties across periods and groups.
- Prepare for next class discussion on electron transfer reactions and oxidation states.