Atomic Models, Periodic Table and Chemical Bonding Essentials

Historical Discoveries and Early Particle Evidence

Faraday; Stoney (coined the name electron in connection with electricity); cathode-ray tube observations (CRT); Thomson (charge-to-mass ratio of the electron); Millikan (electron charge); Goldstein (canal rays); Aston (mass spectrometer).

Atomic Models and Development

Atomic models—development and key ideas:

• Thomson: plum-pudding model; early ideas from scattering and particulate experiments.
• Rutherford: nuclear atom obtained from alpha-particle scattering; nucleus-centered model. (Reference: neutron discovery by Chadwick.)
• Bohr: combines Rutherford's nuclear atom and Planck's quantum concepts — energy is absorbed or emitted in quanta; discrete postulated orbits; quantized angular momentum L = n·(h/2π); electrons emit electromagnetic radiation when transitioning between orbits.
• Sommerfeld: refinement with elliptical orbits and relativistic corrections.
• Current: quantum mechanics — Heisenberg uncertainty principle and Schrödinger's equation govern electron behavior and wavefunctions.

Periodic Table Evolution

Historical steps in the development of the periodic classification:

• Triads (Dobereiner).
• Telluric series ideas (Chancourtois).
• Octaves (Newlands).
• Horizontal table (Mendeleev).
• Meyer and Mendeleev (short-form periodic boards and complementary work).

Applications: discovery of new elements and prediction of properties. From periodic trends one can deduce physical and chemical properties; periodic law must be validated experimentally.

Defects historically noted: hydrogen's placement, irregularities in sequence, lack of continuity or clear relationships in some areas, and quantitative valence anomalies. Periodic classification separates metals and nonmetals but has limitations in some specific valence or continuity cases.

Chemical Bonding: Ionic, Covalent and Metallic

Ionic Bonding and Born–Haber Concepts

Ionic bonding (Lewis octet rule): ions form to achieve noble-gas electron configurations. Typical energetic and physical characteristics:

• Formation energy: energy released in formation of 1 mol of an ionic solid from gaseous ions.
• Born–Haber cycle terms (schematic): -Q = S + 0.5 × D + I - EA - U (net energy). (S = sublimation, D = bond dissociation energy, I = ionization energy, EA = electron affinity, U = lattice energy; signs depend on convention.)
• Proposed properties: high melting points, high enthalpies of vaporization, characteristic cation/anion radii (r+ / r-), solubility in polar solvents with solvation, and electrical conduction when molten or in solution (electrolysis possible).

Covalent Bonding

Covalent bonding (Lewis octet or duet as applicable):

• Homomolecular and heteromolecular cases: polar versus nonpolar covalent character depends on electronegativity differences.
• Theories and models: valence bond theory (localized bonds), resonance (delocalization), and molecular orbital theory (bonding/antibonding orbitals).

Metallic Bonding

Metallic bonding: delocalized electrons form energy bands. Key notes on alloys and metal solids:

• Electron bands of energy explain electrical conductivity and metallic properties.
• Alloys: substitutional and interstitial types; solvent and solute atoms; solid solutions and stoichiometric intermetallic compounds.

Gases and Gas Laws

Fundamental gas relations and principles:

• Avogadro: at constant pressure and temperature, V ∝ n (volume proportional to amount of substance).
• Boyle (Mariotte): at constant temperature and mass, V ∝ 1/P (inverse relation between pressure and volume).
• Charles (Gay-Lussac): at constant pressure and mass, V ∝ T (volume proportional to temperature in kelvin).
• Gas kinetic theory: molecular interpretation of pressure, temperature, and speeds.
• Dalton: total pressure of a gas mixture is the sum of partial pressures: P = p1 + p2 + ... + pi (pi = xi P for ideal gases and mole fraction xi).
• Graham: laws of diffusion and effusion (rates related to molar masses).
• Van der Waals equation: correction for real-gas behavior (finite molecular volume and intermolecular attractions) and compression deviations.

Solids and Intermolecular Forces

Types of solids and interactions:

• Molecular solids: molecules occupy lattice sites; typically held by weak forces, low melting and boiling points, soft and deformable, not electrically conductive. Nonpolar molecules: London dispersion forces. Polar molecules: dipole–dipole and hydrogen bonding.
• Atomic (covalent) solids: high melting points, hard, strong directional bonding (e.g., diamond, quartz).
• Ionic solids: high melting points, crystalline lattices, electrically insulating in solid state, conductive when molten or dissolved.

Solutions: Dissolution and Factors

Dissolution processes and controlling factors:

• Solid–liquid dissolution: "like dissolves like" — solubility depends on the nature of the solvent and solute, agitation, and temperature.
• Liquid–liquid distribution: partition or distribution principles (e.g., partition coefficient; historical references such as Parkes and distribution phenomena).
• Gas–liquid solubility: Henry's law (at constant temperature, solubility ∝ partial pressure of the gas over the liquid; S = kP).

Colloids and Colloidal Properties

Colloidal systems and characteristic effects:

• Tyndall effect: scattering of light by colloidal particles produces visible beams.
• Brownian motion: random motion of colloidal particles due to solvent molecule collisions.
• Electrophoresis: movement of charged colloidal particles in an electric field.
• Stability: micelle formation and solvation (lyophilic systems), ion adsorption and surface charge effects (lyophobic systems).
• Coagulation / Flocculation (precipitation): addition of electrolytes can neutralize stabilizing charges (+ and −), causing coagulation; dialysis can remove small ions. Lyophobic sols are not peptized easily; lyophilic sols can be peptized or stabilized by solvent affinity.
• Processes to control colloids: electrostatic stabilization, steric stabilization (affinity for solvent), peptization by adding suitable agents (for lyophilic behavior).

Notes: This document preserves the original content while correcting spelling, grammar, punctuation, and capitalization; it organizes topics into headings and lists for clarity and improved SEO.