Classification of Matter Composition of matter Physical and chemical properties Physical and chemical changes Pure Substances A pure substance is a substance that cannot be broken down into simpler components by physical means. Examples: elements and compounds. Elements are substances that are composed of all the same atoms. Examples of Elements What elements do we use everyday? Carbon- graphite in pencils, diamonds Copper- electrical wires, pennies Oxygen- breathing There are 90 elements found in nature. More than 20 others have been synthesized in the lab. Compounds A compound is a substance in which the atoms of two or more elements are combined in fixed proportions. Chlorine and Sodium are toxic alone but when put together in a 1:1 ratio, they make up salt. Mixtures A mixture is a material made up of two or more substances that can easily be separated by physical means. There are two types of mixtures: Heterogeneous mixtures Homogeneous mixtures Heterogeneous Mixtures A mixture in which the different materials are easily distinguishable is a heterogeneous mixture. Heterogeneous mixtures contain more than one phase. A phase is a region with uniform properties, like density, structure and heat capacity. Homogeneous Mixtures A homogeneous mixture contains gaseous, liquid or solid substances blended evenly throughout. Example: cold soft drink A solution is a type of homogeneous mixture of particles so small that they cannot be seen with a microscope and will never settle. Example: vinegar Colloids Colloid comes from a Greek word for glue. Colloids have some properties of heterogeneous and homogeneous mixtures. Examples: milk, paint, fog Like a solution, the components won’t settle if left standing. Like a heterogeneous mixture, there are varying proportions of components. Detecting colloids One way to distinguish a colloid from a solution is by its appearance. Colloids scatter light because the particles suspended are large. The scattering of light by a colloid is called the Tyndall effect. Suspensions A suspension is a heterogeneous mixture containing a liquid in which visible particles settle. Example: muddy pond water Physical Properties A physical property is any characteristic of a material that you can observe without changing the identity of the substances that make up the material. Examples of physical properties: color, shape, size, melting point, boiling point, heat capacity, mass Behavior Some physical properties describe the behavior of a substance. Ductility- the ability of a metal to be drawn into wires Magnetism- the ability to be attracted by a magnetic field Malleability- the ability of a metal to be hammered into thin sheets Behavior Viscosity- the resistance of a fluid to flow Using Physical Properties to Separate How might you separate a mixture of iron and sand? What approach would you take to separate salt from water? What does it mean if a sample has two different boiling points? Physical Change A change in shape size or state of matter is called a physical change. These changes may require energy changes, but the material itself remains unchanged. Examples of state changing processes: freezing, melting, evaporation, sublimation, boiling, condensation Distillation The process of distillation involves the physical separation of substances in a mixture by the evaporation of a liquid and recondensing of its vapor. This process is often used in industry. Natural oils, such as mint and lavender, are separated using distillation. Closed v. Open Systems A closed system is a system which is isolated so that it cannot exchange matter or energy with its surroundings and can therefore attain a state of thermodynamic equilibrium. Example: hand-boiler distillation An open system is a system across whose boundaries both matter and energy may pass. Example: water cycle Chemical Properties A chemical property is a characteristic of a substance that indicates whether it can undergo a chemical change. One such property is flammability. Some chemicals are photosensitive and decompose when exposed to light. Chemical properties are often related to the structure of a particular molecule or compound. Detecting Chemical Change There are 4 clues that a chemical change is taking place: 1. A color change is observed. 2. Heat is released or absorbed. 3. A precipitate is formed. 4. A gas is released. ☺A precipitate is a solid that forms as a result of mixing two or more solutions. Chemical Changes The only real proof that a chemical change or reaction has occurred is a new substance is produced. For example, what forms on iron when exposed to oxygen? Is this a chemical or physical change? Does the separation of an element from its ore require chemical or physical changes? Intensive and Extensive Properties Intensive properties do not depend on the amount of matter present. Examples: melting point, boiling point, density and conductivity of electricity and heat Extensive properties depend on the amount of matter present. Examples: mass, volume and amount of energy Is mass lost during a chemical reaction? Wood is combustible, meaning that it will readily burn. Will the pile of ash remaining after the wood is burned weigh the same as the original log? Where did the excess weight go? You might realize that if you combined all of the oxygen that escaped along with the other gases… the before and after products would be the same!!! The Law of Conservation of Mass This law states that the reactants and the products in a chemical reaction have exactly the same mass. Antoine Lavoisier came up with this law.