Final answer:
Water molecules are polar with a slight negative charge on the oxygen side and a slight positive charge on the hydrogen side. When a negatively charged balloon is near a water stream, the positive (hydrogen) side of the water molecules is attracted to it, causing the stream to bend toward the balloon.
Step-by-step explanation:
Why Does a Water Stream Bend Toward a Negatively Charged Balloon?
Water molecules are polar because they contain a dipole moment, which is a separation of electric charge causing one side of the molecule to be slightly negative and the other side to be slightly positive. The oxygen atom is more electronegative, and it attracts the shared electrons of the molecule more than the hydrogen atoms do. As a result, the oxygen end of the water molecule has a partial negative charge (delta negative), and the hydrogen end has a partial positive charge (delta positive). In the presence of a negatively charged balloon, the positively charged (hydrogen) side of the water molecules in the stream are attracted to the balloon. This attraction causes the water stream to bend towards the balloon, illustrating the principle that opposite charges attract.
For an observable example, when a positively charged rod, comb, or balloon is brought close to a stream of water, the water molecules can rotate so that their negative sides (oxygen side) align towards the rod. Consequently, the entire stream of water is pulled toward the positively charged object due to the attractive forces between opposite charges.