Hello!
BeH₂ is a linear molecule, while CaH₂ is an angular molecule.
The difference between these two molecules is given by the number of electrons they have. Be is in the 2nd period of the Periodic table, and the ion Be⁺² doesn't have any free electron pairs when bonding to H. Ca is in the 4 period of the periodic table, meaning that it has more electrons, and the ion Ca⁺² has two free electron pairs when bonding to H that makes the molecule angular by pushing the bonds at an angle by sterical hindrance.
Have a nice day!
