definitions- alkanes?

sigma bond?

a type of covalent bond which forms when atomic orbitals overlap head on.

• sigma bonds can rotate freely

bond enthalpy?

the energy required to break one mole of gaseous bonds

complete combustion?

when a compound is burnt in a plentiful supply of oxygen

• when alkanes are combusted, the products are water and carbon dioxide

covalent bond?

the electrostatic attraction between a shared pair of electrons and 2 positive nuclei

electron pair repulsion?

pairs of electrons around a nucleus repel each other so the shape that a molecule adopts has these pairs of electrons positioned as far apart as possible

• as a result, carbon atoms in alkanes have a tetrahedral shape with bond angle of 109.5

incomplete combustion?

when a compound is burnt in a limited supply of oxygen.

• when alkanes are incompletely combusted, the products are water, carbon monoxide and carbon (soot)

initiation?

the first step in a radical substitution mechanism, involving the formation of radicals

london forces?

induced dipole-dipole interactions caused when the random movement of electrons creates a temporary dipole in one molecule which then induces a dipole in the neighbouring molecule

propagation?

the second step of a radical substitution mechanism where a radical reacts with another species

termination?

the last step of a radical substitution mechanism in which 2 radicals react together to form a species which only contains paired electrons