1. Learning Objective Classify matter as a pure substance or mixture by investigating its properties Classification of Matter

2. Pure substances have a defined chemical composition Ex) Mixtures are formed from physically mixing two or more pure substances Ex) Classifications of Matter Pure Substance Defined Composition AluminumAl OxygenO2O2 WaterH2OH2O SugarC 6 H 12 O 6 MixtureComposition Trail mixvaries Sugar watervaries Airvaries

3. Element – pure substance consisting of only one type of atom All known elements are listed in the periodic table Some elements always appear as groups of two – Diatomic elements –– H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 Some elements exist in multiple forms – Carbon exists as graphite or diamond Types of Pure Substances

4. Compound – two or more atoms of different elements chemically combined in a fixed ratio Molecule – group of covalently bonded atoms with a fixed composition Compositions of pure substances are described by formulas – Subscripts in formulas represent how many atoms of that element are present in the compound or molecule Subscripts are written after the element they apply to – C 6 H 12 O 6 has six carbon atoms, 12 hydrogen atoms, and six oxygen atoms Subscripts of 1 are implied rather than written – H 2 O has two hydrogen atoms and one oxygen atom Types of Pure Substances

5. Compounds have different properties from the elements that make them up Ex) Properties of Compounds Pure Substance FormulaPropertiesImageImage Credit SodiumNahighly reactive metal By Dnn87 at en.wikipedia (Transferred from en.wikipedia) [CC–BY–SA–3.0] ChlorineCl 2 highly toxic green gas By W. Oelen (http://woelen.ho mescience.net/sci ence/index.html) [CC–BY–SA–3.0] Sodium chloride NaClstable white crystal eaten everyday By Dubravko Sorić SoraZG on Flickr [CC–BY– 2.0]

6. Law of definite proportions – a chemical compound will always contain the same ratio of elements Law of multiple proportions – if multiple compounds can form from the combination of elements, the elements will always combine in small, defined whole number ratios – Ratio of the elements determines the chemical identity of the compound Ex) Laws Governing Compounds Common Name Elements Present Formula of Compound Ratio of Elements WaterHydrogen & Oxygen H2OH2O2:1 Hydrogen Peroxide Hydrogen & Oxygen H2O2H2O2 2:2

7. Heterogeneous mixture – a mixture that is not uniform throughout – Different properties in different parts of the specimen Homogeneous mixture – a mixture that is uniform throughout – Same properties in different parts of the specimen – Also called a solution Types of Mixtures Heterogeneous Mixture By Victor Blacus (Victor Blacus) [GFDL] Solution

8. Mixtures do not have defined ratios Properties of mixtures are generally a blend of the properties of the substances they are made from Properties of Mixtures Chocolate chip cookies By Rdsmith4 (Own work) [CC–BY–SA–2.5]

9. Separation of mixtures is a physical process – Based on differences in the properties of the substances Separation of compounds is a chemical process – A chemical reaction must occur to break a compound into elements Elements cannot be separated any further Separating Mixtures and Pure Substances Types of Physical Separations Reason for Separation FiltrationParticle Size DistillationDifference in boiling points ChromatographyDifferences in attraction to various liquids or solids

10. Classification of Matter Matter Uniform Throughout Physically Combined Homogeneous Mixture Ex) salt water Chemically Combined Compound Ex) H2O Uncombined Element Ex) Al Not Uniform Throughout Heterogeneous Mixture Ex) oil & water