2.1 Types of Chemical Bonds

Bonding depends on electronegativity

Chemical bonds form when atoms interact to lower potential energy. The type of bond depends on the electronegativity difference between atoms. Large differences (metal + nonmetal) favor ionic bonds (electron transfer). Small differences (nonmetal + nonmetal) favor covalent bonds (electron sharing). Metal atoms bonded together form metallic bonds, where electrons are delocalized in a shared 'sea.'

Three bonding models

Ionic bonding: electrostatic attraction between cations and anions in a lattice, giving high melting points and conductivity when dissolved/molten. Covalent bonding: shared electron pairs between nonmetals, forming discrete molecules or networks. Metallic bonding: cations in a lattice surrounded by mobile valence electrons, explaining conductivity, malleability, and luster.

Structure predicts properties

Bonding type determines macroscopic behavior: ionic compounds are brittle solids that conduct electricity only when melted/dissolved; covalent (molecular) compounds often have lower melting points and don't conduct; metals conduct electricity as solids and are malleable/ductile due to their delocalized electrons allowing atoms to shift without breaking bonds.

Key terms

Ionic bond

Electrostatic attraction between oppositely charged ions, typically formed between a metal and nonmetal via electron transfer.

Covalent bond

A bond formed when two nonmetal atoms share one or more pairs of electrons.

Metallic bond

Bonding in metals where cations are held together by a 'sea' of delocalized valence electrons.

Electronegativity difference and bond type

Large difference → ionic bond; small difference → covalent bond; metal-metal → metallic bond.

Why metals conduct electricity as solids

Their delocalized electrons are free to move throughout the lattice, allowing current to flow even in the solid state.

Try an AP-style question

Which pair of elements is most likely to form an ionic bond?

1. Cl and Cl
2. Na and Cl
3. N and H
4. C and O