Chapter 2: Properties of Matter Section 2.1 Classifying Matter Section 2.2 Physical Properties Section 2.3 Chemical Properties

Section 2.1: Classifying Matter Pure Substances What is Matter? Anything that has mass and takes up space (volume) Based on matter’s composition, it can be divided into Pure Substances and Mixtures.

Section 2.1: Classifying Matter Pure Substances Def.-matter that always has exactly the same composition (ex. Table salt, table sugar) Key Concept: Every sample of a given substance has the same properties because a substance has a fixed, uniform composition. 2 Categories of substances: elements and compounds

Section 2.1: Classifying Matter Elements Def.-a substance that cannot be broken down into simpler substances Key Concept: An element has a fixed composition because it contains only one type of atom.

Section 2.1: Classifying Matter Elements: Examples of Elements Carbon (C), Aluminum (Al)- solid at RT Oxygen (O), Nitrogen (N)- gases at RT Bromine (Br), Mercury (Hg)- liquid at RT

Section 2.1: Classifying Matter Elements: Symbols for Elements Developed in 1813 by Swedish chemist Jons Berzelius Symbols contain 1 or 2 letters Symbols based on Latin names of the elements

Section 2.1: Classifying Matter Compounds Def.-a substance that is made from two or more simpler substances and can be broken down into those simpler substances (elements or other compounds) H2O→2H + O

Section 2.1: Classifying Matter Compounds Properties of a compound differ from the properties of the substances from which it is made. Ex. H and O are gases at room temp.; H2O is liquid at room temp.

Section 2.1: Classifying Matter Compounds Key Concept: A compound always contains two or more elements joined in a fixed proportion. Ex. SiO2- 2 (O) atoms for every 1 (Si) atom Ex. H2O-2 (H) atoms for every 1 (O) atom

Elements vs. Compounds If you see the chemical formula for an element what do you notice? Pb K Li H2 O2 What is different on these formula’s of compounds? H2O CO2 C6H12O6 LiCl NaCl

Section 2.1: Classifying Matter Mixtures 2 types: heterogeneous and homogeneous Retain some of the properties of their individual substances Properties of a mixture are less constant (vary) than the properties of a substance.

Section 2.1: Classifying Matter Mixtures Key Concept: The properties of a mixture can vary because the composition of a mixture is not fixed. **Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture.

Section 2.1 Classifying Matter Mixtures: Heterogeneous and Homogeneous Mixtures Heterogeneous- the parts of the mixture are noticeably different from one another Ex. Sand Homogeneous-the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another Ex. Water, steel

Mixtures Heterogeneous Homogeneous A mixture made up of particles that are uniformly distributed (means that you cant see the separate parts) Ex. Salt water In the ocean you cant see the salt dissolved in the water A mixture made up of particles that are not uniformly distributed (normally you can easily see the separate parts) Ex. Raisin Bran You can see the Raisins, flakes, and the milk.

Section 2.1 Classifying Matter Solutions, Suspensions, and Colloids The size of the particles in a mixture has an effect on the properties of the mixture. Key Concept: Based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid.

Section 2.1 Classifying Matter Solutions Def.-the mixture that forms when substances dissolve and form a homogeneous mixture Ex. Sugar water, salt water, lemonade

Section 2.1 Classifying Matter Solutions *They do not separate into distinct layers over time. *They cannot be filtered. *Light passes through them. The particles in a solution are too small to settle out of the solution, be trapped by a filter, or scatter light.

Section 2.1 Classifying Matter Suspensions Def.-a heterogeneous mixture that separates into layers over time Ex. Amoxicillin, muddy water

Section 2.1 Classifying Matter Suspensions *Suspended particles settle out of a mixture or are trapped by a filter They scatter light in all directions because the particles are large; suspensions are cloudy.

Section 2.1: Classifying Matter Colloids Def.-a mixture that contains some particles that are intermediate in size between the small particles in solution and larger particles in a suspension Ex. Milk, fog

Section 2.1 Classifying Matter Colloids Do not separate into layers Cannot be filtered Since they also contain larger particles, they scatter light

Section 2.2 Physical Properties Examples of Physical Properties Def.-any characteristic of a material that can be observed or measured without changing the composition of the substances in the material Key Concept: Viscosity, conductivity, malleability, hardness, melting point, boiling point, and density are examples of physical properties.

Section 2.2: Physical Properties Viscosity Def.-the tendency of a liquid to keep from flowing (its resistance to flowing) >viscosity, the slower the liquid moves Ex. Corn syrup, honey (high viscosity) Ex. Water (low viscosity) Viscosity usually decreases when a liquid is heated.

Section 2.2 Physical Properties Conductivity Def.-a material’s ability to allow heat flow Conductor-materials that have high conductivity (ex. Metals) Ex. Poor conductor (wood)

Section 2.2: Physical Properties Malleability Def.-the ability of a solid to be hammered without shattering Ex. Most metals are malleable; glass shatters (brittle)

Section 2.2: Physical Properties Hardness Ie. Can the material be scratched easily? Can it be cut easily? Diamond is one of the hardest known materials (can cut glass and steel); aggregated diamond nanorods (hardest; carbon-60 molecules) Stainless steel can scratch copper

Section 2.2 Physical Properties Melting and Boiling Points Melting pt.-the temp at which a substance changes from solid to liquid Boiling pt.-the temp at which a substance boils

Section 2.2 Physical Properties Density Def.-the ratio of the mass of a substance to its volume *can be used to test the purity of a substance Ex. Density of silver=10.5g/cm3 RT *if density of a coin is 9.9 g/cm3 RT then: 1.) the coin is not silver or 2.) the coin contains substances in addition to silver

Section 2.2 Physical Properties Using Physical Properties Key Concept: Physical properties are used to identify a material, to choose a material for a specific purpose, or to separate the substances in a mixture.

Section 2.2 Physical Properties Using Physical Properties: Using Properties to Identify Materials Steps are similar to those used to test for purity Decide which properties to test Do tests on a sample of the unknown Compare the results with the data reported for known materials ID of materials can be crucial to solving a crime.

Section 2.2 Physical Properties Using Physical Properties: Using Properties to Choose Materials Properties determine which materials are chosen for which uses What material is more durable? Is a material more comfortable?

Section 2.2 Physical Properties Using Properties to Separate Mixtures Some properties can be used to separate mixtures Key Concept: Filtration and distillation are two common separation methods.

Section 2.2 Physical Properties Using Properties to Separate Mixtures: Filtration Filtration- a process that separates materials based on the size of their particles small pass through; large are trapped

Section 2.2 Physical Properties Using Properties to Separate Mixtures: Distillation Def.-a process that separates the substances in a solution based on their boiling points Ex. (making freshwater)-Water heated until in gas form; then cooled back to a liquid and collected in a separate container Water has a lower boiling point than compounds dissolved in seawater.

Section 2.2 Physical Properties Recognizing Physical Changes Physical change-what occurs when some of the properties of a material change, but the substances in the material remain the same Water (liquid→gas); Bending metal Actions: slice, cut, heat **Some physical changes are reversible, some are not (Cutting hair)

Section 2.3 Chemical Properties Observing Chemical Properties Chemical property-any ability to produce a change in the composition of matter Key Concept: Chemical properties can be observed only when the substances in a sample of matter are changing into different substances.

Section 2.3 Chemical Properties Observing Chemical Properties: Flammability Def.-a material’s ability to burn in the presence of oxygen Not always a desired property: fabrics Ex. Paper, fuels (highly flammable)

Section 2.3 Chemical Properties Observing Chemical Properties: Reactivity Def.-the property that describes how readily a substance combines chemically with other substances Oxygen-high reactivity; Nitrogen-low reactivity Ex. Oxygen causes iron to rust; rust is brittle and weaker than iron

Section 2.3 Chemical Properties Recognizing Chemical Changes Chemical change- what occurs when a substance reacts and forms one or more new substances Key Concept: Three common types of evidence for a chemical change are a change in color, the production of a gas, and the formation of a precipitate. Precipitate-any solid that forms and separates from a liquid mixture

Section 2.3 Chemical Properties Is a Change Chemical or Physical? Can be difficult to distinguish one from the other Ask the question: Are different substances present after the change takes place? No-physical; Yes-chemical Key Concept: When matter undergoes a chemical change the composition of the matter changes. When matter undergoes a physical change, the composition of the matter remains the same.