Science: An Elementary Teacher’s Guide/Properties of Matter
Properties of Matter
[edit | edit source]Matter is anything that has mass and volume, including all atoms and all subatomic particles, but also all mixtures of compounds, all objects we encounter around us, etc. The properties of matter include any traits that can be measured, such as an object's density, color, mass, volume, length, malleability, melting point, hardness, odor, temperature, and more. Some properties of matter are unchanging, such as the density of gold, while other properties depend on the amount of matter present (such as the mass of a golf ball compared to the mass of a bowling ball) or the properties of the mixture. All atoms of any particular element will share traits of that element, but an element's properties can be changed drastically through chemical reactions. For example, pure sodium is a dull, soft metal that will react explosively in contact with air and water, but sodium that has reacted with chlorine is part of table salt and is very non-reactive.
There are two properties of matter which all substance are distinguished by, they are "physical properties" and "chemical properties."
Physical Properties: include size, shape, color, texture etc. The melting point and freezing point are also physical properties. Every substance has some physical properties that are different from those of other substances (how is wood different than metal or plastic?). Physical properties can be changed, sometimes permanently and sometimes irreversibly. For example, when ice melts the water can then be refrozen but when wood is burned many of its atoms leave as gas (carbon dioxide and water vapor), and the match cannot be put back together to its original state.
Chemical Properties: characteristics that have to do with the chemical makeup of a substance, or how it reacts with other substances. An example of this is when water and vinegar are added to separate portions of baking soda, evidence of different chemical properties can be observed as carbon dioxide begins to bubble up from the baking soda mixed with vinegar but not from the portion to which water had been added. During a chemical reaction a new substance is formed with new and different properties than the original substances.
States of Matter
[edit | edit source]The state of matter describes the distinct form that it takes: solid, liquid, gas, or plasma. There are more than these four states of matter, but we will not discuss them here because they only occur in extreme situations that are not normally encountered on Earth. From Lower Energy --> Higher Energy
Solid
[edit | edit source]Solids can be considered to be hard as a rock or soft as fur. The key to a solid is that it has a definite shape and volume. It holds its shape and wont flow like a liquid. A rock will always look like a rock unless something happens to it. A solid can hold its shape because the molecules are tightly packed together, often held by covalent bonds. In a solid, particles are packed tightly together so they are unable to move about very much (they still have motion but are only able to jiggle in place). Particles of a solid have very low kinetic energy, but can still have high potential energy. The electrons of each atom are still in constant motion, so the atoms have a small vibration but they are fixed in their position. If cooled to absolute zero (0 K) all motion will stop. Increasing pressure will not compress the solid to a smaller volume (you may crush a solid object, thus making it smaller, but really you just removed space between parts of the solid).
Liquid
[edit | edit source]A liquid is something that can change its shape if poured into another container. A liquid can feel wet. Examples of things that are liquid at room temperature include water, blood, gasoline, and lemonade. If you have different types of molecules dissolved in a liquid, it is called a solution. Lemonade is a solution of water, sugar, and lemon; a combination of molecules. In the liquid phase, the particles of a substance have more kinetic energy than those in a solid. The liquid particles are not held in a regular arrangement, but are still very close to each other so liquids have a definite volume. Liquids, like solids, cannot be compressed (this property is useful in hydraulics). Particles of a liquid flow around each other, so liquids have an indefinite shape—a liquid will change shape to conform to its container. Force is spread evenly throughout the liquid, so when an object is placed in a liquid, the liquid particles are displaced by the object.
Gas
[edit | edit source]Gases are everywhere. Solid molecules are tightly compacted together, liquid molecules are less organized and more spread out, while gas molecules are very spread out and disorganized. Gas molecules fill up any container with no consideration to size or shape. Gas particles have a great deal of space between them and have high kinetic energy. If unconfined, the particles of a gas will spread out indefinitely; if confined, the gas will completely fill its container. When a gas is put under pressure by reducing the volume of the container or pumping the gas into a container, the space between particles is reduced and the pressure exerted by their collisions increases. If the volume of the container is held constant, but the temperature of the gas increases, then the pressure will also increase. Conversely, if the pressure is decreased, the temperature will also decrease (you have probably observed this as you spray a can of compressed air and it gets cold). If compressed enough, the molecules may form a liquid (for example, compressed propane is a liquid, but as it is released from the tank it changes back to a gas). Gas particles have enough kinetic energy to overcome intermolecular forces that hold solids and liquids together, thus a gas has no definite volume and no definite shape.
Plasma
[edit | edit source]A plasma is a hot ionized gas consisting of approximately equal numbers of positively charged ions and negatively charged electrons. The characteristics of plasmas are significantly different from those of ordinary neutral gases so that plasmas are considered a distinct "fourth state of matter." Plasma is not a common state of matter here on Earth, but is a very common state of matter in the universe. Plasma consists of highly charged particles with extremely high kinetic energy. The noble gases (helium, neon, argon, krypton, xenon and radon) are often used to make glowing signs by using electricity to ionize them to the plasma state. Stars are essentially superheated balls of plasma.
Quiz
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