AP Chemistry Unit 2: Compound Structure and Properties Notes

Introduction

Bonding models describe how electrostatic attractions and repulsions produce stable arrangements of nuclei and electrons. Ionic, covalent, and metallic labels describe different electron distributions, but real bond character can lie between ideal categories.

Structure is read in stages: determine the electron bookkeeping, compare resonance contributors, count electron domains, predict three-dimensional geometry, and then evaluate bond and molecular polarity.

A drawing is useful only within its limits. Lewis symbols do not show exact electron density, potential-energy curves are not timelines, formula units are not molecules, and hybridization labels are not observed orbital pictures.

Current exam guidance: Aligned to the current 2026–27 AP Chemistry course framework and exam scope.

2.1

Types of Chemical Bonds

What common physical idea holds ionic, covalent, and metallic structures together?

Short answer

Each bonding model describes an electron distribution in which nucleus–electron attractions lower the system’s energy enough to overcome repulsions at a stable arrangement.

Know firstValence electrons · Ion formation · Coulombic attraction

Bond labels describe electron distribution

A chemical bond is not a hook between atoms. It is a stable arrangement of nuclei and electrons produced by competing electrostatic attractions and repulsions. As particles approach from far apart, nucleus–electron attractions can lower potential energy. At very short separation, nucleus–nucleus and electron–electron repulsions rise sharply.

The ionic model places positive and negative ions in an extended array. The covalent model places shared electron density between bonded nuclei. The metallic model spreads valence-electron density across many positive cores. These pictures explain different structures and properties, but they are idealized categories rather than three disconnected laws of nature.

Bond character forms a continuum. Unequal sharing creates partial charges in a polar covalent bond, but no single electronegativity cutoff turns a bond abruptly into an ionic one. Use composition, structure, electron density, and measured properties together; one clue rarely proves a complete bonding model.

Chemistry model

Bond type changes electron distribution

Compare transferred charge, shared density, and delocalized electrons without treating the categories as rigid boxes.

Electron transferIonic · NaCl

Oppositely charged ions occupy an extended lattice.

Shared densityCovalent · H₂

Electron density is concentrated between bonded nuclei.

Delocalized electronsMetallic · Cu

Valence electrons extend through many metal-atom cores.

electronegativity and structure guide the model

Read this figure without the graphic

Bond type changes electron distribution. The figure connects ionic, covalent, metallic so the relationship can be read without relying on color alone.

Representation	What to read
ionic	starting evidence or quantity
covalent	intermediate relationship
metallic	result or conclusion

Three useful bonding models

Model	Electron distribution	Structural unit	Important limit
Ionic	largely localized on ions	extended charge-balanced lattice	not isolated ion pairs
Covalent	shared between bonded nuclei	molecule or network	sharing may be unequal
Metallic	delocalized across many centers	extended metallic solid	electron sea is schematic

Keep these three ideas

All bond models arise from electrostatic energy.
The models differ mainly in electron distribution and structural extent.
Bond character is continuous rather than fixed by one cutoff.

Compound Structure and Properties