Properties of Matter & Chemical Structure – Quick Review

Learning Targets

Determine molecular polarity from structure and $\Delta EN$ .
Identify intermolecular forces (IMF) and link them to polarity.
Relate IMF strength to boiling point, solubility, and physical state.

Chemical Bonds

Ionic Bond

Metal $+$ non-metal; complete electron transfer.
Produces cations/anions arranged in crystal lattice.
Properties: very high $T<em>m$ / $T</em>b$ , solids are non-conductive (conduct when molten/aqueous).

Covalent Bond

Between non-metals; electrons are shared.
Molecules stay intact; phase changes break only IMF, not bonds.
Properties: low $T<em>m$ / $T</em>b$ , generally poor conductors.

Metallic Bond

Metal atoms share a "sea" of mobile valence electrons.
Explains conductivity, malleability, formation of alloys.

Electronegativity & Bond Polarity

$\Delta EN = |EN<em>{1}-EN</em>{2}|$
- $\Delta EN = 0$ ⇒ non-polar covalent.
- 0 < \Delta EN \le 1.8 ⇒ polar covalent.
- \Delta EN > 1.8 ⇒ ionic.
Unequal sharing creates bond dipoles (arrow points to more electronegative atom).
Molecular polarity depends on both bond dipoles and geometry (vector sum).

Compound Types

Ionic compounds: neutral lattices of ions, formula shows ratio (e.g., $\mathrm{NaCl}$ ).
Molecular (covalent) compounds: discrete molecules, formula shows atoms per molecule (e.g., $\mathrm{H_2}$ ).

Intermolecular Forces (IMFA)

IMF	Acts Between	Key Requirement
Dipole–Dipole	Polar molecules	Permanent dipoles align (+ to –).
Hydrogen Bond	Molecules w/ $\mathrm{N! -! H}$ , $\mathrm{O! -! H}$ , $\mathrm{F! -! H}$	H attached to N/O/F attracted to lone pair on another N/O/F.
London Dispersion (LDF)	All atoms & molecules	Instantaneous dipoles from electron motion.

Relative strength: \text{H-bond} > \text{Dipole–Dipole} > \text{LDF} (all << ionic/metallic/covalent bonds).

Effects of IMF on Physical Properties

Stronger IMF ⇒ higher $T<em>m$ / $T</em>b$ (e.g., water vs $\mathrm{Br_2}$ ).
Like-dissolves-like: polar substances dissolve in polar solvents via dipole or H-bond interactions; non-polar dissolve in non-polar via LDF.
Physical state at room T: strong IMF (ionic, metals, H-bonded) ⇒ solids; weak IMF (non-polar) ⇒ gases/liquids.

Quick Reference

Ionic lattice → very high $T_b$ , soluble in polar solvents.
Polar covalent + H-bonding (water, alcohols) → moderate $T_b$ , high surface tension.
Non-polar molecules (noble gases, $\mathrm{I<em>2}$ , hydrocarbons) → low $T</em>b$ , insoluble in water, IMF dominated by LDF.