Question

Describe the motion of molecules in a solid .Why
is gold only present in the solid state?

Answer 1

Motion of particles in a solid
- Particles (atoms, ions or molecules) in a solid occupy fixed positions in a regular (crystalline) or irregular (amorphous/glassy) arrangement.
- They do not translate freely; instead they vibrate about their equilibrium positions. These vibrations increase in amplitude with temperature.
- Because the particles are tightly bound, a solid has a definite shape and volume and only very slow diffusion of atoms (practically negligible on short timescales).
- When the vibration amplitude becomes large enough (at the melting point) the bonds holding the lattice together break and the solid turns into a liquid.

Why gold is solid under ordinary conditions
- At ordinary temperatures (room temperature) the thermal energy available to atoms (kT ≈ 0.025 eV) is far too small to overcome the strong metallic bonding between gold atoms (bond energies of order electron‑volts). That keeps gold atoms fixed in a lattice so gold is a solid.
- Gold crystallizes in a face‑centered cubic (fcc) metallic lattice; the delocalized “sea” of electrons in metallic bonding gives strong cohesion.
- Gold’s melting point is 1 064 °C and its boiling point is about 2 856 °C, so at normal temperatures and pressures it exists as a solid. If heated above its melting point it becomes liquid, and at still higher temperatures it vaporizes.
- (Extra note) Relativistic effects in this heavy element affect its electron orbitals and influence properties such as bond strengths and color, which also play a role in its solid-state behavior.