Ionic, Covalent & Metallic Bonding

You’ll be able to

Classify a bond as ionic, covalent, or metallic from the atoms involved
Explain the sea-of-electrons model of metallic bonding
Predict conductivity, melting point, and malleability from bonding type

Three ways atoms hold together

Bonding type follows the atoms' pull on electrons. Ionic bonding transfers electrons from a metal to a nonmetal, producing oppositely charged ions locked in a rigid lattice. Covalent bonding shares electron pairs between two nonmetals. Metallic bonding pools the valence electrons of many metal atoms into a shared "sea." The size of the electronegativity difference tells you which regime you are in.

Bond type from electronegativity difference (ΔEN)

ΔEN ≳ 1.7 → ionic · 0.4–1.7 → polar covalent · < 0.4 → nonpolar covalent

These cutoffs are approximate guides, not hard walls — bonding is a continuum from pure sharing to full transfer.

The sea-of-electrons model

In a metal, each atom releases its valence electrons into a delocalized "sea" that flows freely around a lattice of fixed positive cores (the nuclei plus inner electrons). Nothing binds a given electron to a given atom. This mobile sea is the single idea that explains why metals conduct electricity and heat, shine, and bend without shattering.

Structure dictates properties

Ionic solids are hard, brittle, and high-melting because every ion is locked by strong electrostatic attraction; they conduct only when molten or dissolved, once the ions are free to move. Molecular (covalent) compounds are held internally by strong bonds but attracted to each other only weakly, so they melt low and do not conduct. Metals conduct in the solid state (the sea carries charge) and are malleable — the electron sea simply re-forms when layers of cores slide past one another.

Watch out

Why does an ionic crystal shatter but a metal bends? Strike an ionic lattice and a layer shifts so like charges align — the repulsion cracks it apart. In a metal the electron sea is nondirectional, so shifted layers stay bonded and the metal deforms instead of breaking.

Worked example

Solid X is brittle, melts at 801 °C, does not conduct as a solid, but conducts readily when melted. Identify its bonding type and justify it.

1.A very high melting point signals strong forces holding the whole solid together — a lattice, not weak molecular attractions.
2.Brittleness points to a rigid array of charged particles that repel when displaced.
3.The conductivity clue is decisive: no conduction as a solid (ions are locked in place) but conduction when molten (ions become mobile).
4.These three properties together are the signature of an ionic compound (this is NaCl).

Answer: Ionic bonding — a lattice of fixed ions that only carry charge once melting frees them to move.

Checkpoint

Which property is best explained specifically by the mobile "sea of electrons" in a metallic solid?

Checkpoint

A substance melts at −57 °C and does not conduct electricity in any state. What type of substance is it most likely to be?

Checkpoint

Using electronegativity values (Na = 0.9, Cl = 3.0, O = 3.4, C = 2.6), which bond is the most ionic in character?

On the exam

The AP exam constantly links a property to a structural cause. Never just name the bond type — state the mechanism: "conducts when molten because the ions become mobile" or "malleable because the nondirectional electron sea allows cores to slide."

Answer the 3 checkpoints as you read.