Water

Changing Phase H 2 O ( l )  H 2 O ( g ) H 2 O ( l ) Spacing Freedom of movement H 2 O ( g ) Spacing Freedom of movement

What keeps the water particles as close as they can get?

Water drops are high and round.

Claim: a statement about the particles. The high round drop can be explained using a model of particle attractions.

Particles of a liquid are free to move and gravity pulls them down. If only gravity were the only force acting on the particles, the drop would look like this. Water Drop- high and round on wax paper

Focus on the particle colored red. How many water particles does it touch when the drop is flat? How many water particles does it touch when the drop is high and round?

The Claim: Water particles are attracted to other water particles.

The water particles are free to move in the liquid and gravity pulls them down. Since the drop is not flat, there must be some force holding it up. The force of attraction between water particles must hold up the drop.

Additional Evidence: Observations. We can see it.

Evidence: Two drops brought near each other- pull together to make one drop Link. T

Evidence: Wet toothpick pulls water up from the drop Link. T

Evidence: Water drops stay together when dragged. Link. T

table top wax paper The water particles must be more attracted to the table particles than to the wax paper particles. The attraction between the particles pulls the drop flatter on the table.

Alcohol particles must be less attracted to other alcohol particles than water particles to other water attractions. wax paper water drop wax paper alcohol drop The flat drop shows less attraction between the particles. The alcohol drop leaves a trail behind instead of staying together when dragged. This also shows less attraction between the particles.

Oil dropped in water

Oil slick floats on water

Water drops in water. The drops stay round and sink to the bottom.