Most liquids the students recognize are beverages they drink, such as fruit juices. Liquids have no shape of their own, so they are able to effortlessly change their shape. The molecules are densely packed together allowing them to freely move about and flow. Liquids have fluidity, the ability to flow. The liquid will take the shape of the container it is being poured into. The molecules within some liquids can be attracted to the sides of the container they are being placed into. The attraction is referred to as adhesion, which allows a liquid to stick to solids, in this case the sides of its container. When a liquid is cooled it transforms into a solid and when it is heated it becomes a gas.
As liquids reach their freezing point they begin to enter the solid phase. When most liquids freeze they contract and will take up less space. However, the exception is water, which will take up more space. As the temperature of a liquid is lowered it will make the molecules slow down and move together. Over time the liquid freezes and becomes a solid.
Fast moving molecules at the surface of a liquid, will break the bonds keeping it in the liquid and the liquid evaporates. The amount of a liquid's surface that comes into contact with air affects the liquids ability to evaporate into a gas. The molecules on a liquid's surface are attracted to both the air molecules above them and the liquid molecules below them. Surface tension is created as the molecules of the liquid pull together. A smooth covering forms as the top of the water tightens up due to the tension created. The strong bonds between molecules in a liquid give the liquid cohesion. Cohesion allows molecules to stick together and form bonds. Cohesion is the reason behind observing liquids in the form of droplets or round shapes. Molecules clump together forming little round drops.
As liquids are continuously heated, its molecules move around quickly, which makes the bonds between them break. The molecules move around faster as the liquid becomes warmer. As molecules move around they collide with one another, breaking the bonds holding them together. Liquids have the ability to spread out so more of the molecules can escape into the air. The molecules will rise, escape and become a gas. As a liquid is heated it will release vapor and will eventually evaporate and enter the gas phase.