What is waters characteristic shape due to

In polar covalent bonding, electrons are shared unequally between atoms, due to the unequal distribution of electrons between atoms of different elements, slightly positive and slightly negative charges appear in different parts of the molecule.

In this context, water molecule is an exellent example of this type of bonding:

Water () can stick to itself through hydrogen bonds, because a water molecule consists of 2 hydrogen atoms attached to 1 oxygen atom.  

The oxygen atom tends to monopolize more electrons and keeps them away from hydrogen. Then, it can be said that a water molecule will have a negative side (oxygen) and a positive side (hydrogen).  

Thanks to this polarity, water molecules can stick together with the formation of hydrogen bonds to attract a partial positive charge of hydrogen and a more electronegative atom, such as oxygen.

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.