An Educational Guide to the Phases of Water
Earth is one special planet. It has liquid water, oxygen, plate tectonics, and an atmosphere that shields all life forms from the sun's rays. In fact, Earth provides everything necessary to sustain life. Without its unique features, we would not exist. All life forms, including humans, rely on the planet's elements to live. Humans need oxygen to breathe, food to eat, and water to drink. The latter has its own story to tell.
Water is an essential part of the ecosystem. It covers 70 percent of the Earth's surface in three forms, including gaseous, liquid, and solid states. It can be seen as rainfall, clouds, icebergs, or lakes. It can also be felt in a humid environment. Water's special qualities stem from the unique shape of the water molecule. Each water molecule is made up of two hydrogen atoms and an oxygen atom. The side with the two hydrogen atoms has a positive charge. The other side, with the oxygen atom, has a negative charge. When two water molecules come together, the negative side of the water molecule clings to the positive side of another water molecule. This amazing process is known as hydrogen bonding, and it creates one of the phase changes of water.
Water as a Solid
Water can appear in its solid state as ice. When water solidifies, the water molecules are packed closely together to prevent it from changing shape. It forms into a solid state of matter, which can be seen in the form of hail storms and icebergs in nature. Unlike other solid states of matter, ice floats on liquid water. When the water hydrogen atoms bond, they leave enough room between the crystals to allow this phenomenon to occur. This means that ice is less dense than liquid water. Ice forms when the temperature drops below 0 degrees Celsius or 32 degrees Fahrenheit.
Water as a Liquid
When temperatures rise above freezing, ice melts to become liquid water. As a liquid, the magnetic pull between molecules begins to weaken. This allows individual molecules to move around each other. As a result, the liquid phase change of water occurs. After this phase change, the increased movement of molecules allows the liquid to take the shape of any container. It can also freely move around in an open environment, as seen in lakes, rivers, and oceans. The abundance of liquid water makes life plentiful on Earth.
Water as a Gas
When temperatures rise above 100 degrees Celsius or 212 degrees Fahrenheit, water evaporates to become a vapor. In its gaseous state, the water molecules move very rapidly without bonds between them. Although it is invisible to the naked eye, water in its gaseous state can be felt on a hot, humid day. Many people believe that this phase change of water can be seen when boiling water on a stove. Boiling water produces steam or condensation, not water vapor. Steam is actually very small water droplets suspended in the air. Water vapor can be observed through the lens of infrared-sensing instruments.
Water Cycle on Earth
Each of the phase changes of water occur in the Earth's natural water cycle. In fact, the water on Earth now is the same water that existed thousands of years ago. The same water that rains on your house during thunderstorms also rained on the dinosaurs. The Earth's natural water cycle is responsible for re-circulating water to create bodies of water, clouds, and precipitation. The first step in the water cycle is evaporation, which comes mostly from the oceans. The second step is condensation, which forms clouds in the air. The final step is precipitation, which falls from the clouds in the sky. Precipitation can fall in both liquid and solid form, as rain or snow. Once the precipitation reaches the ground, it can either melt or evaporate to restart the water cycle all over again.
Follow these links to learn more about the three phase changes of water:
- American Museum of Natural History: Three Phases of Water
- Water Phases: Gas, Liquid, and Solid
- Water Phase Diagram
- The Story of Drinking Water: What Forms Can Water Take?
- The Many Phases of Water (PDF)
- The Water Cycle
- The 3 States of Matter
- Energy Involved in the Phase Changes of Water
- The States of Water: Solid, Liquid, Gas
- All About Phase Changes
- States of Water: Water Exists in Three States: Gas, Liquid, and Solid
- The Hydrological Cycle
- The Earth's Natural Water Cycle
- Student Activity: The Water Cycle
- Water Cycle Experiment
- Phase Diagrams of Pure Substances
Written By: Lynn Taylor