Question

Why do compounds conform to certain shapes?

Answer 1

if you mean structures like cubic cristaline structure is because type of bonds made in the compund, electronegativity of atoms and vaan der walls forces.
thermodinamicaly approach: compounds form structures because the state of energy is the lowest at that form.

Answer 2

vaan? is this thermodynamically?

Answer 3

yes its thermodynamically mathematicaly and all other -aly's :D
compounds can be gasses, liquids and solids (lets say just this three states of mater) so it has to do with how many electrons which atom has, hybridization of orbitals (hybridization is mixing of orbitals - s, p, d, f) so lets give example of every three states:
CO - is linear molecule due to bonding with (sigma) and (pi) bonds something like this C=O so it is linear
H2O - forms tetrahedron cause O has 2 pairs of electrons and sp3 hibridization so with 2 hydrogens it forms tetrahedron
NaCl - is solid and it has crystaline structure it forms cubic lattice
if you still are unclear just say

Answer 4

it pretty much relies on the forces between Bonded pairs of electrons and Lone pairs of electrons surrounding an atom in a compound. depending on how many electron bonds and pairs change the angles at which the connections are.