Exploring Matter: Physical and Chemical Properties and Changes

1. Matter – anything that has mass and takes up space (has volume) is matter • Pure substance – matter that always has exactly the same composition (ex: table salt, sugar). • Every sample of a given substance has the same properties because a substance has a fixed, uniform composition. Physical Science: Ch 2 Notes Element – a substance that cannot be broken down into simpler substances. An element has a fixed composition because it contains only one type of atom. There are 118 elements and they are organized into the Periodic Table of Elements. Compound – a substance that is made from two or more elements. A compound always contains two or more elements joined in a fixed proportion.

2. Mixture – a material consisting of two or more substances. The properties of a mixture can vary because the composition of a mixture is not fixed Heterogeneous mixture – a combination of two or more substances that are not uniformly dispersed (often composed of more than one phase of matter) Physical Science: Ch 2 Notes Suspension– a heterogeneous mixture that separates into layers over time. A filter can be used to separate the parts of a suspension Homogeneous mixture – a combination of two or more substances that ARE uniformly dispersed (often called solutions) Solution– formed when substances dissolve and form a homogeneous mixture that does not separate into layers and is transparent

3. B. Physical Properties – any characteristic of a material that can be observed or measured without changing the composition of the substances in the material Viscosity – the tendency of a liquid to keep from flowing, or its resistance to flowing Physical Science: Ch 2 Notes honey has a high viscosity so it moves slowly the viscosity of a liquid usually decreases when it is heated • Conductivity – a material’s ability to allow heat to flow materials that have a high conductivity are called conductors metals are good conductors if a material is a good conductor of heat, it is usually a good conductor of electricity • Malleability – the ability of a solid to be hammered without shattering most metals are malleable

4. Melting Point – the temperature at which a substance changes from a solid to a liquid (also called the freezing point) for water, the melting point is 0 °C Physical Science: Ch 2 Notes • Boiling Point – the temperature at which a substances changes from a liquid to a gas for water, the boiling point is 100 °C • Density – the ratio of an objects mass to its volume Density can be used to test the purity of a substance since the densities of pure substances are usually known and recorded

5. C. Using Physical Properties – physical properties are commonly used in the following three ways • 1. Using Properties to Identify Materials Step 1 – Decide which properties to test Physical Science: Ch 2 Notes Step 2 – Perform tests on a sample of the unknown Final Step – Compare the results with the data reported for known materials (look up the density or melting point values) • 2. Using Properties to Choose Materials Properties determine which materials are chosen for which uses (ex: diamonds are used in rings because they “last forever” unlike softer materials) • 3. Using Properties to Separate Mixtures Filtration – a process that separates materials based on the size of their particles. Distillation – a process that separates the substances in a solution based on their boiling points (ex: boiling seawater convert it to fresh water)

6. D. Chemical Properties – a property of matter that describes a substance’s ability to participate in chemical reactions (and therefore change the composition of matter) Flammability – a material’s ability to burn in the presence of oxygen Reactivity – a property that describes how readily a substance combines chemically with other substances E. Physical versus Chemical Changes Physical Change – occurs when some of the properties of a material change, but the substances in the material remain the same (ex: heating butter, folding paper, braiding hair) Some physical changes can be reversed while some cannot be reversed (ex: cutting hair, slicing a tomato) Chemical Change – occurs when a substance reacts and forms one or more new substances. (ex: baking a cake, burning paper, dying hair) There are four common types of evidence for a chemical change: • 1. Color Change (jewelry tarnishes) • 2. Production of a Gas (baking soda with vinegar makes carbon dioxide) • 3. Production or loss of heat • 4. Formation of a Precipitate – any solid that forms and separates from a liquid mixture