Chapter 2: Properties of Matter

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

2. 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.

3. 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

4. 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.

5. 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

6. 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

7. 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

8. 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.

9. 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

10. 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 Elements vs. Compounds

11. 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.

12. 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.

13. 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

14. 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. Mixtures Heterogeneous Homogeneous

15. 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 asolution, a suspension, or a colloid.

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

17. 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.

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

19. 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.

20. 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

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

22. 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.

23. 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.

24. 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)

25. 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)

26. 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

27. 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

29. 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

30. 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.

31. 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.

32. 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?

33. 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.

34. 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

35. 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.

36. 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)

37. 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.

38. 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)

39. 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

40. 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

41. 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.