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What is one physical characteristic of a solid? Solids can be hard like a rock, soft like fur, a big rock like an asteroid, or small rocks like grains of sand. The key is that solids hold their shape and they don't flow like a liquid. A rock will always look like a rock unless something happens to it. The same goes for a diamond. Solids can hold their shape because their molecules are tightly packed together. You might ask, "Is baby power a solid? It's soft and powdery." Baby power is also a solid. It's just a ground down piece of talc. Even when you grind a solid into powder, you will see tiny pieces of that solid under a microscope. Liquids will flow and fill up any shape of container. Solids like to hold their shape.
Solid MixturesSolids can be made of many things. They can have pure elements or a variety of compounds inside. When you have a solid with more than one type of compound, it is called a mixture. Most rocks are mixtures of many different compounds. Concrete is a good example of a man-made solid mixture.Granite is a mixture you might find when you hike around a national park. Granite is made of little pieces of quartz, mica, and other particles. Because all of the little pieces are spread through the rock in an uneven way, scientists call it a heterogeneous mixture. Heterogeneous mixtures have different concentrations of compounds in different areas of the mixture. For example, there might be a lot of quartz and very little feldspar in one part of the granite, but only a few inches away those amounts might flip. CrystalsAllotropesA diamond is another good example of a crystal. Diamonds are a crystal form of pure carbon (C). The carbon atoms of a diamond are connected in a very compact and structured way. The carbon atoms found in graphite (in pencils) have a different crystalline arrangement. According to the Mohs hardness scale, diamonds are very hard with a value of 10 while graphite is very soft with a value of 1.5. The two different structures of carbon atoms (tetrahedron versus hexagon) are called allotropes.
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Earth is the only known body in our solar system that has liquid water existing freely on its surface; life on Earth would not be possible without the presence of liquid water. Water has several properties that make it a unique substance among substances. It is an excellent solvent; it dissolves many other substances and allows those substances to react when in solution. In fact, water is sometimes called the universal solvent because of this ability. Water has unusually high melting and boiling points (0°C and 100°C, respectively) for such a small molecule. The boiling points for similar-sized molecules, such as methane (BP = −162°C) and ammonia (BP = −33°C), are more than 100° lower. Though a liquid at normal temperatures, water molecules experience a relatively strong intermolecular interaction that allows them to maintain the liquid phase at higher temperatures than expected. Unlike most substances, the solid form of water is less dense than its liquid form, which allows ice to float on water. In colder weather, lakes and rivers freeze from the top, allowing animals and plants to continue to live underneath. Water also requires an unusually large amount of energy to change temperature. While 100 J of energy will change the temperature of 1 g of Fe by 230°C, this same amount of energy will change the temperature of 1 g of H2O by only 100°C. Thus, water changes its temperature slowly as heat is added or removed. This has a major impact on weather, as storm systems like hurricanes can be impacted by the amount of heat that ocean water can store. Water’s influence on the world around us is affected by these properties. Isn’t it fascinating that such a small molecule can have such a big impact?
Naming examples of solids, liquids, and gases is a common homework assignment because it makes you think about phase changes and the states of matter.
Solids are a form of matter that has a definite shape and volume.
Liquids are a form of matter that has a definite volume but no defined shape. Liquids can flow and assume the shape of their container.
A gas is a form of matter that does not have a defined shape or volume. Gases expand to fill the space they are given.
Depending on the temperature and pressure, the matter may transition from one state into another:
Increasing pressure and decreasing temperature forces atoms and molecules closer to each other so their arrangement becomes more ordered. Gases become liquids; liquids become solids. On the other hand, increasing temperature and decreasing pressure allows particles to move father apart. Solids become liquids; liquids become gases. Depending on the conditions, a substance may skip a phase, so a solid may become a gas or a gas may become a solid without experiencing the liquid phase. |
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