Properties of covalent molecules & allotropes of carbon

Melting and boiling points

melting and boiling points of covalent substances are lower than metallic and ionic substances

→ the stronger the intermolecular forces in a covalent substance, the higher the melting/boiling temperature

Conductivity

Covalent substances are non-conductive as they do not contain charged particles (free-moving electrons)

Diamond

formed of carbon atoms bonded to four other carbon atoms in a tetrahedral, covalent network lattice

Properties of diamond

• hardest naturally occurring substance, but also brittle

• does not conduct electricity (no free-moving charged particles)

• high thermal conductivity

Graphite

Layers of 2D hexagonal lattices, where each carbon is bonded to three others and the fourth is delocalised and able to move within its layer

layers are held together by weak dispersion forces

Properties of graphite

• conducts heat and electricity

• hardness depends on directionality; layers can slide over each other

• soft and slippery

• high sublimation point