(a) In the vapour state, BeCl2 tends to form a chlorobridged dimer which dissociates into the linear monomer at high temperature of the order of 1200K.
(b) In the solid state, BeCl2 has a chain structure. In this structure, each Be atom is surrounded by chlorine atoms i. e., two Cl-atom by covalent bonds and other two Cl-atoms by co-ordinate covalent bond. The chain structure is shown as below: