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BONDING & PROPERTIES - Coggle Diagram
BONDING & PROPERTIES
ATOMIC FOUNDATIONS
Solid-state matter: building units may be atoms, molecules, ions or crystals.
Atom: nucleus contains protons (+) and neutrons (0); electrons (−) occupy shells/orbitals.
Atomic number Z = protons; neutral atom: p = e; neutrons N; mass number A ≈ Z + N.
Atomic weight = weighted average of naturally occurring isotopes. 1 amu = 1/12 the mass of C-12.
1 mole = 6.023 × 10²³ particles; 1 amu/particle = 1 g/mol.
Bohr model: discrete orbits and quantized energies. Wave-mechanical model: electron cloud / probability distribution.
Quantum numbers: n (shell size), ℓ (subshell shape), mℓ (orbital state/orientation), ms (spin ±½).
PERIODIC TABLE & ELECTRONS
Pauli exclusion principle state that each electron state holds at most 2 electrons with opposite spins.
Filled s and p subshells are generally stable
elements in a column have similar valence structures
Electropositive elements (left side) tend to lose electrons → cations
Electronegative elements (right side) tend to gain electrons → anions.
Higher electronegativity means stronger tendency to attract electrons.
Electronegativity 0–0.4 covalent , 0.5–1.7 polar covalent , >1.7 ionic
BONDING FORCES & ENERGIES
Atoms experience attractive force FA and short-range repulsive force FR; net force FN = FA + FR.
As atoms approach, electron clouds overlap and repulsion rises. At equilibrium: FA + FR = 0.
Equilibrium distance r₀ (or lattice constant a₀): stable separation where net force is zero and potential energy is minimum.
Bonding / binding energy E₀ or Eb: energy per atom needed to separate it from a solid; a measure of bond strength.
Bonding / binding energy E₀ or Eb: energy per atom needed to separate it from a solid; a measure of bond strength.
Generally, larger bonding energy means a higher melting temperature Tm and a deeper energy well.
Example: Boron has smaller atomic size and much larger Eb (187 eV) than Al (72.7 eV), consistent with lower thermal expansion.
PRIMARY BOND
Electrons transfer from one atom to another, producing positively charged cations and negatively charged anions
Bond arises from Coulombic / electrostatic attraction between opposite charges
Usually forms between highly electropositive metals and highly electronegative nonmetals
Nondirectional: bond strength acts similarly in all directions around an ion.
Ionic solids are hard, brittle, and electrical / thermal insulators.
Example: Na transfers its 3s electron to Cl → Na⁺ + Cl⁻
COVALENT & METALLIC BONDS
COVALENT
Adjacent atoms share electrons; each atom contributes at least one electron. Strongly directional.
Approximate bond count: an atom with N′ valence electrons can bond to at most 8 − N′ other atoms (lecture example: Cl, N′ = 7 → 1 bond).
Examples: H₂, Cl₂, CH₄, H₂O, HF, diamond, Si, Ge, GaAs and SiC. Bond strength / Tm ranges from very high (diamond) to weak (e.g., bismuth).
Real bonds can be partly ionic and partly covalent; ionic character increases with electronegativity difference.
METALLIC
Valence electrons are delocalized as a “sea of electrons” around positive ion cores; bonding is nondirectional.
Mobile electrons explain high electrical and thermal conductivity. Metals are ductile because bonds can break and reform during deformation.
Metallic bond strength and Tm vary widely: Hg is low; W is high (3410°C in the lecture table).
SECONDARY BONDS & MATERIAL PROPERTIES
Van der Waals bonds arise from electric dipoles: the positive end of one dipole attracts the negative end of another.
They occur between virtually all atoms or molecules; typical energy is about 10 kJ/mol (~0.1 eV/atom), often between molecules / polymer chains.
Secondary / physical bonds are weaker than primary bonds, but can still strongly influence physical properties.
Hydrogen bonding is another secondary bond; examples in lecture: NH₃, 35 kJ/mol (0.36 eV); H₂O, 51 kJ/mol (0.52 eV).
Bond-energy / melting-point examples: diamond 7.4 eV, >3550°C; W 8.8 eV, 3410°C; NaCl 3.3 eV, 801°C; H₂O 0.52 eV, 0°C; Ar 0.08 eV, −189°C.
Bond type and strength help explain conductivity, ductility, hardness, brittleness and melting temperature.