Inorganic Chemistry Fundamentals of Inorganic Chemistry Lecture - 01

Inorganic Chemistry Fundamentals of Inorganic Chemistry Lecture - 01 By Mohit Dadheech Sir

Overview of Topics Covered

1. Zeff and Other Important Properties
2. Geometry and Hybridization of Molecules
3. Fajans' Rule

Valence Shell and Electrons

• Definition of Valence Shell:
  • The outermost shell of an atom which contains valence electrons.
  • Example electron configurations:
  • Sodium (Na): 1s² 2s² 2p⁶ 3s¹
  • Magnesium (Mg): 1s² 2s² 2p⁶ 3s²

Screening Effect / Shielding Effect

• Definition: The effect where inner shell electrons reduce the effective nuclear charge experienced by outer shell electrons.
• Explanation: Inner electrons create a repulsive force that shields outer electrons from the nucleus's positive charge, thus reducing attraction.
• Mathematical Representation:
  • If Z is the total number of protons, then:
  • For an electron in the nth shell, the equation can be represented as:
    $Z_{eff} = Z - S$
  • Where S is the shielding constant (number of inner electrons).

Order of Shielding in Different Subshells

• The general order of shielding effectiveness is as follows:
  • s > p > d > f

Effective Nuclear Charge (Zeff)

• Definition: The net attractive power of the nucleus on outer electrons after they are shielded by inner electrons.
• Formula:
  • $Z_{eff} = Z - S$
• Application: This concept helps in understanding trends in atomic properties such as size and ionization energy.

Contraction in Size due to Zeff Changes

• As Zeff increases (due to poor shielding from d and f electrons):
  • Outer electrons feel a stronger attraction leading to contraction in atomic size.
  • Thus,
  • For the order: s > p > d > f

Lanthanoid and Actinoid Contractions

• Lanthanoid Contraction:
  • Occurs due to poor shielding (σ) from 4f electrons, leading to increased Zeff and contraction as the atomic number increases from Ce to Lu.
• Actinoid Contraction:
  • Similar effects from 5f electrons.
• Order of Shielding: Poor shielding is noted as σ = d > f.

Size of Group 13 (Boron Family)

• Size order based on common group 13 elements:
  • B < Ga < Al < In < Tl
• Contraction trends as we progress down the group.

Isoelectronic Species and Size Trends

• Definition of Isoelectronic Species: Atoms or ions that have the same number of electrons.
• Example:
  • $Ne, Na^+, Mg^{2+}$ (All have 10 electrons).
• Size of species changes with nuclear charge, with more positive charge resulting in smaller size due to increased Zeff.

Electronegativity

• Definition: A qualitative measure of the tendency of an atom to attract a bonding pair of electrons.
• Characteristics:
  • It is a unitless quantity and varies depending on the type of bond and the element involved.
  • Important in predicting bond character (ionic vs covalent).

Bond Polarity and Ionic Character

• If the electronegativity difference between two atoms in a bond increases, the ionic character of that bond increases.
  • For example,
  • Covalent Bonds: When electronegativity difference is small,
  • Ionic Bonds: When the difference is large.

Pauling Scale of Electronegativity

• Values: Listing of common elements and their electronegativity values exhibits a range from low (Li=1.0, Na=0.9) to high (Fluorine, F=4.0) across non-metals and metals.

Acidic and Basic Nature of Oxides and Hydroxides

• Characteristics:
  • Non-metal oxides/hydroxides are typically acidic.
  • Metal oxides/hydroxides are generally basic.
• Example reactions:
  • $N_2O_5 + H_2O <br /> ightarrow HNO_3$ (Acidic)
  • $CaO + H_2O <br /> ightarrow Ca(OH)_2$ (Basic)

Comparison of Acidic and Basic Nature

• Determinants include:
  • Electronegativity (EN) values; higher EN correlates with more acidic behavior.
• Examples of acidic oxides include CO₂, N₂O₅, while basic oxides include CaO, MgO.

Amphoteric Oxides

• Definition: Oxides or hydroxides capable of acting as both acids and bases.
  • Examples include ZnO, Al₂O₃, SnO₂.

Fajan's Rule and Covalent Character in Ionic Compounds

• Fajan's Rule: Suggests that ionic bonds can have covalent character based on:
  • Size of the cation (smaller cations lead to distortion of anion's electron cloud).
  • Charge of the cation (higher charge leads to polarizing power).

Conclusion for Maximum Covalent Character

1. Small cations are more polarizing.
2. Large anions lead to greater polarizability.
3. Greater charge on anions increases polarizability and covalent character.

Geometry and Hybridization of Molecules

• Method to Determine Geometry: Using the formula for determining the hybridization:
  • ext{Hybridization} = rac{(n+m)}{2}
    where n is the number of atoms connected and m is the number of lone pairs.
• Common Shapes and Hybridization:
  • Linear: AB₂
  • Trigonal Planar: AB₃
  • Tetrahedral: AB₄
  • Trigonal Bipyramidal: AB₅
  • Octahedral: AB₆

Covalent Bond Formation

• Defined as the sharing of electrons with atomic orbitals merging called overlapping.

Important Notes on Valency and Covalency

• Valency: The capacity of an atom to bond (in terms of the number of electrons it can gain, lose, or share).
• Covalency: The total number of covalent bonds (σ and π) an atom can form in a molecule.

Sample Molecular Geometry Calculations

• Step-by-step identification of geometry using provided electron configuration examples:
  • Example: SO₃
  • Determining electron pairs and hybridization leads to predicting trigonal planar geometry.

Review Questions

• Various multiple-choice questions assessing understanding of concepts including:
  • Basic vs acidic oxides, isostructural species, shape determination, and the interpretation of Fajan's rule principles.