Ch. 2 Learning Objectives 1. I can classify pure substances. This means that I know the difference between an element and a compound. 2. I can describe the characteristics of an element. This means that I know how elements are identified by using chemical symbols. 3. I can describe the characteristics of a compound. The means that I know the difference between a compound and other pure substances. 4. I can distinguish a pure substance from a mixture. This means that I know what makes them different.

Learning Objectives Continued 5. I can classify mixtures. This means that I know what a homogeneous and heterogeneous mixture is. I also know what a solution, suspension, and colloid is. 6. I can describe the physical properties of matter. This means that I know what each property is and how we can identify them. 7. I can describe how to separate a mixture. This means I can differentiate between filtration and distillation. 8. I can describe the chemical properties of matter. This means I can list the different properties. 9. I can describe how to tell that a change has a occurred. This means I can state the three ways to tell a change has happened.

Section 2.1: Classifying Matter

Pure Substances Matter that always has exactly the same composition is classified as a pure substance. Examples: salt and sugar

**Every sample of a given substance has the same properties because a substance has a fixed, uniform composition. Substances are classified into two categories: elements and compounds.

Elements An element is a substance that cannot be broken down into simpler substances. An atom is the smallest particle of an element. **An element has a fixed composition because it contains only 1 type of atom. No two elements contain the same type of atom.

Examples of Elements Solid elements at room temperature Aluminum carbon Gas elements at room temperature Oxygen Nitrogen Liquid elements at room temperature Bromine Mercury

Symbols for Elements Jons Berzelius, a Swedish chemist, suggested that chemists use symbols to represent elements. Characteristics of symbols: 1 or 2 letters (First letter is always capitalized) Still used on the periodic table today. Why is using symbols important? So there is a universal symbol for all languages.

Compounds Water is composed of the elements hydrogen and oxygen Compounds Are made from two or more simpler substances that can be broken down into those simpler substances. Always contain 2 or more elements joined in a fixed proportion.

Mixtures **Properties can vary because the composition of a mixture is not fixed. (this means the composition can change)

Mixtures In a heterogeneous mixture, the parts of the mixture can be classified and noticeably different from one another.

Mixtures continued In a homogeneous mixture, substances are so evenly distributed that it is difficult to distinguish one substance from another in the mixture. Appears to be only one substance.

Solutions, Suspensions, and Colloids Based on the size of its largest particles a mixture can be classified as a solution, a suspension, or a colloid

Solutions When substances dissolve and form a homogeneous mixture, the mixture that forms is called a solution. Example: sugar and water Liquid Solutions Do not separate Can not be filtered Clear **The particles in a solution are too small to settle out of the solution, be trapped by a filter, or scatter light

Suspensions Is a heterogeneous mixture that separates into layers over time. Example: sand and water Can a suspension be filtered?

Colloids A colloid contains some particles that are intermediate in between small particles in a solution and the larger particles in a suspension. Do not separate into layers Can not be filtered Examples: Fog

Physical Properties A physical property is any characteristic of a material that can be observed or measured without changing the composition of substances in a material.

Examples of Physical Properties Viscosity Conductivity Malleability Hardness Melting point Boiling point Density

Viscosity The resistance to flow The greater the viscosity the slower the liquid moves High viscosity liquids: honey, corn syrup Low viscosity liquids: vinegar, water Viscosity will decrease when the liquid is heated.

Conductivity Ability to allow heat to flow Materials with high conductivity are called conductors. Example: Metals

Other Properties Malleability – the ability of a solid to be hammered without shattering. Hardness – diamond is the hardest know material Density – is used to test purity of a substance Melting and Boiling Points When a material has reached its melting point the material changes from a solid to a liquid

Using Physical Properties How are physical properties used: To identify a material To choose a material for a specific purpose To separate substances into a mixture

Using Properties to Identify Materials What are the three steps used to identify a material? Decide which properties to test Test on the unknown sample Compare results with data for known materials Why is identifying a material important? To solve crimes

Using Properties to Separate Mixtures What are the two separation methods? Filtration- the process that separates materials based on the size of the particles. Distillation- process that separates the substances in a solution based on their boiling points. Example: providing fresh water

Recognizing Physical Changes When does a physical change occur? When some of the properties of a material change, but the substances in the material stay the same. Two examples: ice melting and hair styles

Observing Chemical Properties What is a chemical property? Any ability to produce a change in the composition of matter. When can a chemical property be observed? Only when the substances in a sample of matter are changing into different substances.

What are the two examples of chemical properties? Flammability – material’s ability to burn in the presence of oxygen Reactivity – how readily a substance combines chemically with other substances. Oxygen is a highly reactive element and nitrogen has an extremely low reactivity.

Recognizing Chemical Changes When does a chemical change occur? When a substance reacts and forms one or more new substances. Examples of a chemical change Baking a cake Ripening bananas Leaves on a tree changing color

Evidence of a chemical change Change in color Production of gas Formation of precipitate

Ask yourself… Are different substances present after the change takes place?

Key Point When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter stays the same.

Homework Page 58 Section 2.3 Assessment Questions # 4-8