MATTER Since the study of chemistry is the study of matter and the changes it goes through we need to know what is considered matter and how it is classified. Below you will find some information about matter. matter - anything that takes up space (has volume) and has mass mass - a measure of the amount of matter in an object Mass is used as the measurement of the amount of matter in an object because it is a constant. The volume of an object can change with temperature and the weight of an object can change with location. Matter normally exists in 3 states (phases). Solids matter with with definite shape and volume solids usually have a high density compared to their liquid or gas form solids only expand slightly when heated solids are almost incompressible Liquids matter that flows and takes the shape of its container liquids have a fixed volume liquids are usually less dense than their solid form (water is the exception) liquids only expand slightly when heated liquids are almost incompressible Gases matter that takes the shape and volume of its container gases are less dense than their solid or liquid form gases expand without limit when heated gases are easily compressed The terms gases and vapor are often used interchangeably, but in science their is a difference between the two. The term gas is used for a substance that normally exists as a gas at room temperature, like oxygen. The term vapor is used for a substance that normally exists as a liquid or solid at room temperature, like water. Water can exist in the gaseous state in the air at room temperature, but normally it is found in the liquid state. It is possible for matter to exist in a fourth state under extreme conditions. This fourth state of matter is called plasma. Plasma is a gas that has been heated to a very high temperature. When a gas is heated to high temperatures the molecules separate into atoms and electrons are stripped from the atoms. In order to form plasma a gas must be heated to temperatures of 50,000 °C or higher. Matter can be classified into two main categories, Pure Substances and Mixtures. Pure Substances - matter that has a uniform and definite composition. All pure substances have the same properties and characteristics. For example, pure water (H2O) has the same properties and characteristics whether it is found in Minnesota or in Africa. Pure substances can be either elements or compounds. Element - An element is the simplest form of matter that cannot be broken down into other substances. Elements can be found on the Periodic Table and there are 109 of them, of which 91 are found in nature. Examples of elements are: sulfur, iron, oxygen, hydrogen Compound - A compound is a substance that is made up of two or more elements chemically combined. Elements in a compound can only be separated by a chemical reaction. Examples of compounds are: NaCl, H2O, CO2 Mixtures - a physical blend of 2 or more substances where each substance retains its properties. An example would be a mixture of sugar and salt. Each substance retains its properties and they can be separated by physical means (without a chemical reaction). Mixtures are either homogeneous or heterogeneous. Homogeneous Mixture - a mixture with uniform composition throughout (evenly distributed). Homogeneous mixtures are also called solutions in chemistry. Examples would be: saltwater, homogenized milk, or brass (a mixture of copper and zinc). Heterogeneous Mixture - a mixture that is not uniform in composition. The substances are not evenly distributed in this type of mixture and they may even contain more than one phase. Examples would be: vegetable soup, soil, or pizza. We can describe and identify matter by physical and chemical properties. We can also observe matter undergoing change during physical and chemical changes. Physical Property - a property that can be observed without changing the substance's composition. Examples sould be: density, melting points, boiling points, color, odor, or hardness. All of these properties can be measured or observed without changing the compostion of the substance. Chemical Property - a property that describes the ability of a substance to undergo a chemical reaction and form a new substance. For example, a chemical property of sodium is that it will react in water to form hydrogen gas and sodium hydroxide. Extensive Property – a property that depends on the amount of matter in the sample. Examples would be mass, weight, and volume. Intensive Property – a property that does not depend on the amount of matter in the sample. Examples would be density, melting and boiling points. Physical Change - altering a substance without changing its composition. Examples would be: cutting, tearing, melting, boiling, or grinding. You can perform any of these actions on a substance without changing what it is made of. Chemical Change - a change that results in the formation of 1 or more new substances. Chemical changes cannot take place without a chemical reaction occuring. Examples would be: rusting of iron, or burning of paper. In each example one or more new substances are forming. Chemical Reactions When a chemical reaction takes place the starting substances in the reaction are called reactants and the new substances that form are called products. Chemical equations are an abbreviated way to show what is reacting and what is forming in a chemical reaction by using the symbols of the elements involved. An example of a chemical reaction is: solid sodium metal reacts with chlorine gas to yield solid sodium chloride with the release of heat. The chemical equation for this reaction is shown below. Na(s) + Cl2(g) ------------------- 2NaCl + heat Reactants Products The reaction shown above is exothermic because heat is released in the reaction. In an exothermic reaction heat is shown on the side with the products. A reaction where heat is taken in is said to be endothermic and the heat is shown on the side with the reactants. In any reaction, whether it is physical or chemical, the total energy on the reactants side must equal the total energy on the products side. This is true because of the Law of Conservation of Energy which states: energy cannot be created or destroyed in any physical or chemical reaction; energy is just converted from one form to another. Energy that is stored (potential energy) in the substances reacting gets converted into other forms of energy, such as heat. In an exothermic reaction the reactants have more stored (potential) energy than the products since the stored energy of the products plus the heat released must equal the total energy of the reactants. In an endothermic reaction the stored energy of the products is greater than the stored energy of the reactants because the reactants are taking in heat to increase their total stored energy. Element Types & the Periodic Table The periodic table is a tool used in chemistry that has elements arranged in rows (periods) and columns (groups) based on the elements properties. The left side of the periodic table is composed of metals and the upper right side of the periodic table is composed of nonmetals. The diagonal stairway in outlined on our periodic table on the wall is the boundary between these two types of elements. Elements that border on the stairway are called metalloids and can have properties of both metals or nonmetals, depending on conditions. The following properties are associated with the different types of elements. Metals Good conductors of electricity and heat Malleable (can be pounded into sheets) Ductile (can be stretched into wires) Lustrous (shiny) Nonmetals Poor conductors of electricity and heat Brittle Non-lustrous (with a very few exceptions) The nonmetals in the far right column on the periodic table are called Noble gases and are very unreactive. They are found in very few compounds while most of the elements on the rest of the periodic table react with each other to form many different compounds.