Properties of Matter
You use characteristics to identify and classify everything around you. When you are grocery shopping, you can tell the difference between a carrot and potato simply by looking at them. You could even tell the difference between an orange and apple without seeing them simply by the way their skin feels. Properties can be used to identify any type of matter.
Color, shape, and size are physical properties of matter. A physical property of matter is a characteristic that can be observed without changing the matter into a different substance. Each substance has a unique set of physical properties that distinguishes it from all other substances. Some physical properties, such as texture and hardness, describe how an object feels. These properties are observed by looking at or touching an object. You can observe whether matter is smooth or rough and hard or soft.
Some physical properties, such mass and volume, are determined by making measurements. Mass is the amount of matter in an object, and volume is the amount of space matter takes up. The mass and volume of an object can be used to find another physical property-density. Density is the amount of mass in a given volume, and it is a unique property of matter that is useful in separating and identifying substances.
Physical properties can be used classify and identify matter, but some properties are more helpful than others. Physical properties such as density, temperature, and color do not change when the amount of matter changes. Some of these properties, such as density, are characteristic of a substance. For example, a single drop of pure water and five gallons of pure water both have a density 1.0 g/mL. Other physical properties, such as mass and volume, do change when the amount of matter changes. A full glass of water has a greater volume and mass than half a glass of water.
Over time, the surface of a shiny silver spoon will become dull and black because silver tarnishes when exposed to air. The ability to tarnish is a chemical property of some types of matter. A chemical property is the ability or inability of a substance to react with or change into one or more new substances.
Like physical properties, chemical properties are used to classify substances. Unlike physical properties, however, chemical properties occur only when the composition of a substance changes. This means that a new substance must be formed. Chemical properties cannot be determined by looking at or feeling the substance or by taking measurements.
Have you ever seen a rusty old car, tractor, or set of tools? All these objects may develop rust, a flaky, reddish-brown substance that can form on some metals when the metals are exposed to air. The ability to rust is a chemical property of iron and metals that contain iron. When iron combines with oxygen and water in air, rust forms. Rust has a different chemical composition than that of the iron from which it formed. You can determine if a substance has the ability to rust only by observing the formation of rust.
Another chemical property is flammability, which is the ability to burn. Paper and wood are examples of matter that have the ability to bum. Matter that is described as flammable, such as paper, wood, gasoline, and many cleaning products, can burn easily and quickly. As with physical properties, every substance has a certain set of chemical properties. Silver can tarnish, but it does not rust or burn. Iron can rust, but it is less flammable and does not tarnish.
|Physical Properties That Depend on Amount||Physical Properties That Do Not Depend on Amount||Chemical Properties|
|mass||boiling point||ability to tarnish|
|volume||color||ability to rust|
|size||density||ability to burn|
|hardness||ability to react with oxygen|
Think about Science
Directions: Answer the following questions.
- Which physical property would be most useful when trying to identify a substance? A. density B. flammability C. mass D. shape
- Which property can be observed only by the formation of a new substance? A. ability to rust B. color C. melting point D. texture
Changes of State
A glass of ice water sits in front of you on the table. It is obvious the water in the glass is both a solid, which is the ice, and a liquid. There is also water vapor in the air, which is a gas. Solid, liquid, and gas are all states of matter, which are the physical forms in which all matter exists. The state of matter is a physical property that depends on temperature and pressure. A change of state is the conversion of a substance from one physical form to another. The composition of a substance does not change as the substance is converted from one state to another. When ice cream melts on a warm day, it changes from a solid to a liquid. Although they look different, both the solid ice cream and the melted ice cream contain the same molecules.
When matter changes from one state to another, thermal energy is absorbed or released. When matter is heated, it absorbs thermal energy. Matter releases thermal energy as it cools. Substances need to be heated or cooled to a certain temperature to change state. The temperatures at which a substance changes from one state to another do not depend on the amount of the substance. The melting point is the temperature at which a solid changes into a liquid. The boiling point is the temperature at which a liquid changes into a gas. The melting and boiling points of water are the same whether there are two or twenty liters of water.
The change from the solid state to the liquid state is called melting. A substance must absorb thermal energy to melt. The particles in a solid vibrate more vigorously as the thermal energy and the temperature of the solid increase. At the melting point, the particles vibrate so intensely that the attractive forces between them are overcome, and the particles begin to move past one another. The temperature of the substance stays constant while the solid changes to a liquid. A substance has a characteristic melting point that can help identify it. For example, the melting point of water is 0°c , whereas the melting point of table salt is 801 °c.
The change of state from a liquid to a solid is called freezing. Freezing is the reverse of melting, so the freezing point of a substance is the same as its melting point. However, to change a liquid into a solid, the liquid must be cooled. As a liquid is cooled, it loses thermal energy, and its particles slow down and come closer together. At the freezing point, the attraction between the particles overcomes their motion. The temperature stops decreasing as the liquid becomes a solid.
The change of state from a liquid to a gas is called vaporization. A substance needs to absorb thermal energy to change from a liquid to a gas. There are two ways vaporization occurs: boiling and evaporation.
Vaporization that occurs throughout a liquid is called boiling. When a liquid boils, gas bubbles form within the liquid and rise to the surface. A liquid boils only when its temperature reaches its boiling point. At that temperature, the particles have enough energy to overcome the attractive forces between them. The particles are free to spread apart, and the liquid changes into a gas. Like the melting point, the boiling point can be used to identify a substance. The boiling point of water is 100° C at sea level.
A puddle formed during a rainstorm disappears as sunlight shines on it because of evaporation. Evaporation is vaporization that occurs only at the surface of a liquid and at temperatures below the boiling point of a substance. The water molecules on the surface of the puddle absorb energy from the Sun. Once they have absorbed enough energy, the particles spread apart, and the liquid water changes into water vapor. The water molecules become dissolved in the air.
Droplets of water form on glass when water vapor cools and condenses. The change of state from a gas to a liquid is called condensation. Condensation is the reverse of boiling and occurs when a gas cools. As a gas releases thermal energy, its particles slow down, and its temperature drops. When the particles slow down enough for the forces of attraction to pull them together, the gas changes into a liquid
Under certain conditions, matter can change from a solid directly to a gas. The change of state in which a solid changes directly to a gas is called sublimation. During sublimation, the particles of a solid absorb enough energy so that they change from being held very close together to being very far apart. You may have seen fog for special effects made by the sublimation of dry ice, which is solid carbon dioxide.
Think about Science
Directions: Answer the following questions.
- Which is a change of state from a gas to a liquid? A. boiling B. condensation C. freezing D. sublimation
- During which change do the particles in a substance gain enough energy to begin moving past one another? A. boiling B. evaporation C. freezing D. melting
You can use the periodic table to predict the physical and chemical properties of elements. Knowing whether an element is a nonmetal, metal, or metalloid can help you predict several general physical properties. Knowing the group of an element can help you predict its chemical properties.
Physical Properties and the Periodic Table
Metals, most of which are found on the left and middle of the periodic table, share some general physical properties. Metals tend to be shiny solids with high melting points. Only one metal, mercury, is a liquid at room temperature. Many metals are a silvery gray color, although there are some exceptions, including copper and gold. Metals are also good conductors of heat and electricity and tend to be able to be made into wires or hammered into different shapes without breaking. The density and hardness of metals varies, with the transition metals tending to be denser and harder than the alkali and alkaline earth metals. Some metals are magnetic, including cobalt iron, neodymium, and nickel.
The physical properties of nonmetals, found to the right of the zigzag line m the periodic table, tend to be more varied than those of metals. Many nonmetals are gases, although a few are solids, and bromine is a liquid at room-temperature. The solids tend to be brittle, dull, nonmagnetic, and poor electrical conductors, but there are some exceptions. One form of carbon diamond, is extremely hard, but it does not conduct electricity well. Another form of carbon, graphite, can conduct electricity.
The seven metalloids, located between the metals and nonmetals in the periodic table, have properties of both. All metalloids are solids at room temperature. They can be shiny or dull, brittle or able to be shaped. Metalloids typically conduct heat and electricity better than nonmetals but not as well as metals. Whether a metalloid acts as a conductor depends on conditions such as temperature, light, and whether it’s mixed with other certain elements.
The group of an element can sometimes be helpful in predicting physical properties. For example, the elements in group 1 and group 2 are softer and less dense than the transition metals found in groups 3 through 12. The noble gases in group 18 are all colorless gases. However, groups 13 through 17 contain metals, nonmetals, and metalloids, so, for these groups, the group does give not a good indication of expected physical properties.
Chemical Properties and the Periodic Table
As you have learned, the ability of an element to form bonds depends on the outermost electrons in the atoms of that element. This and other chemical properties of elements vary in a regular way within the groups of the periodic table. Elements in the same group have similar chemical properties because they have the same number of electrons in their outermost electron shell. The outermost electron shell is the highest electron shell that contains electrons. The electrons in this shell are the only electrons that are shared or exchanged to form chemical bonds.
The chemical properties of elements can also be predicted by the location of an element in a period of the periodic table. Chemical properties change regularly across a period because the number of outermost electrons increases across a period. The group number indicates the number of valance electrons. For example, all the elements in group 1 have one outermost electron, and elements in group 2 have two outermost electrons. For groups 13 through 18, the number of electrons in the outermost energy level is the group number minus ten.
The metals in group 1 are slightly more reactive than those in group 2. However, both groups of elements are very reactive because they can transfer one or two electrons to another element to have a full outermost energy level. None of these elements are found alone in nature because they combine so readily with other elements. The transition metals, found in groups 3 through 12, are less reactive, although many still have the ability to react with oxygen and other nonmetals. A few transitions metals, such as gold, rarely react. The halogens, group 17, are nonmetals and are very reactive because they need to gain only a single electron to have a full outermost energy level. On the other hand, the noble gases, group 18, are inert, which means they are very un-reactive. They have a full outermost energy level and are found as uncombined atoms in nature.
Properties of Materials
Very few of the materials around you are made of a single element. Some materials are compounds, but most are complex mixtures. The chemical composition of a compound can help you predict the properties of a compound because the properties are the result of interactions between the atoms, ions, or molecules that make up the compound. By understanding these interactions, scientists and engineers can design materials that have specific properties. For example, they can make steel that is stronger than pure iron or polymers that are rigid or flexible.
Think about Science
Directions: Answer the following questions
- Based on its position in the periodic table, which element would you expect to conduct electricity? A. chlorine (Cl) B. nitrogen (N) C. phosphorus (P) D. silver (Ag)
- Based on its position in the periodic table, which element would you expect to be the most reactive? A. argon (Ar) B. cobalt (Co) C. magnesium (Mg) D. silicon (Si)