Understanding the variation of a material’s properties with size, form of aggregation and dimensionality is becoming important in the face of increasing miniaturization of electronic and mechanical devices, experimental. studies have focused on the preparation and characterization of solid-scare nanometre-scale structures such as metal and semiconductor nanocrystals(1-3), surface-supported structures and quantum dots(4) and nanoscale junctions or wires(5-22). It has emerged that these nanostructures can often be fruitfully described using concepts and methodologies developed in the contexts of gas-phase atomic clusters and atomic nuclei(23-25). Here we make this connection explicitly through first-principle molecular dynamics simulations(22,26) which show that, as nanowires of sodium metal are stretched to just a few atoms in diameter, the structures formed by metal atoms in the neck can be described in terms of those observed in small gas-phase sodium clusters(27). We find that the electronic spectral and conductance characteristics of these atomic-scale contacts exhibit dynamical thermal fluctuations on a sub-picosecond timescale, owing In rearrangements of the metal atoms, which will significantly affect the transport properties of such nanowires.