Atomic Structure, Chemical Bonding, and Molecular Forces

Atomic Structure and Electron Configuration

• Atomic number = number of protons
• Mass number = protons + neutrons
• Isotopes differ by the number of neutrons

Quantum Mechanics and Orbital Rules

• Orbitals: s (1 orbital), p (3), d (5), f (7)
• Aufbau Principle: Electrons fill the lowest energy orbitals first.
• Hund’s Rule: Electrons spread out before pairing up in orbitals.
• Pauli Exclusion Principle: No two electrons can have the same set of quantum numbers.

Photoelectron Spectroscopy (PES) Basics

• X-axis: Binding energy (values increase to the left).
• Peak height: Corresponds to the number of electrons.
• Position: Peaks farther to the left are closer to the nucleus.

Chemical Bonding and Electronegativity

Ionic and Covalent Bonds

• Ionic bond: Attraction between oppositely charged ions.
  • Forms between a metal and a nonmetal.
  • Electrons are transferred, not shared.
• Covalent bond: The sharing of electrons.
  • Forms between nonmetals.
• Electronegativity: The ability of an atom to attract electrons.
  • Increases across a period and up a group.
  • A larger electronegativity difference leads to a more polar bond.

Bond Polarity and Lewis Structures

• Nonpolar covalent: Equal sharing of electrons.
• Polar covalent: Unequal sharing of electrons.
• Ionic: Extreme polarity.
• Lewis structures show valence electrons only.
  • Single bond = 2 shared electrons
  • Double bond = 4 shared electrons
  • Triple bond = 6 shared electrons
• Octet rule: Atoms generally want 8 valence electrons.

VSEPR Theory and Molecular Geometry

Intermolecular Forces and Physical Properties

Types of Intermolecular Forces (IMFs)

Intermolecular forces (IMFs) are attractions between molecules. They are weaker than covalent and ionic bonds. Listed from strongest to weakest:

1. Hydrogen bonding: Occurs when H is bonded to N, O, or F. This is the strongest IMF.
2. Dipole–dipole forces: Occur between polar molecules where opposite partial charges attract.
3. London dispersion forces: Present in all substances. These increase with molar mass and surface area.

Impact of IMFs on Physical Properties

Stronger IMFs lead to:

• Higher boiling point
• Higher melting point
• Higher viscosity
• Higher surface tension

Solubility and Dissolution

The general rule is “like dissolves like”:

• Polar substances dissolve in polar solvents.
• Nonpolar substances dissolve in nonpolar solvents.