This causes attraction between the H of one molecule and the O of another, which results in a weak bond called a Hydrogen bond . Note that heating something, or changing its state requires energy. When it reaches 0 degrees C, it begins to melt. 1 degree for each calorie added. Its vapor pressure increases with temperature, to the point where it equals atmospheric pressure, and it starts to boil.
H bonds cause water to want to stick together.
A measure of how easily it flows. As it heats it expands, so the density of warmer water is less, because H bonds are less and less common. However, as it cools the H bonds begin to take up more space. Electrical current does not flow through pure water very easily. This helps them to separate from each other and therefore dissolve, releasing some heat.