Chem 121 1st Edition Lecture 2 Outline of Last Lecture I. GradingII. Class Survival TipsOutline of Current Lecture II. What is Chemistry? III. What is Matter?a. Categories of matterIV. Pure SubstancesV. Mixtures vs. CompoundsVI. Scientific Approach to KnowledgeVII. 3 Natural Laws of MatterCurrent LectureWhat is chemistry? The study of composition, structure, properties and changes of matter and energy along with the changes that matter undergoes.What is matter? Anything that has mass and occupies spaceCategories of matter:- Pure Substances- composed of single type of matter, with one type of atom or molecule (examples: table sugar, gold)- Mixtures- composed of at least two types of pure substances (examples: milk, air, tap water)Pure Substances: -Element: composed of one type of atoms-CANNOT be broken down to simpler substances chemically- Gold, Bromine, Helium-Compound: composed of two or more elements in fixed and definite proportions-Broken down to simpler substance chemically- Water, Sugar, Carbon DioxideThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Homogeneous Mixtures:- Need two different pure substances (compounds)- No visible boundaries, can see through it- Can’t be seen with the naked eye- Extremely small (which is why we cant see any boundaries)- Clear and transparent in liquid and gas - Mixed as individual atoms, ions, and molecules- Aqueous solution: solution in which water is solventHeterogeneous Mixtures:- Do not mix, must be at least one or more visible boundaries- Opaque and muddy in liquid and gas- Ice water is a pure substance, no matter state. (Not compounded)- Compounds are different atoms chemically bonded togetherMixtures vs. CompoundsMixtures maintain identity, separated in pure substances (Sea water  sea salt)Compounds lose their identity, broken in elements (water with electricity will split)To tell the difference… ask yourself “Are there any other pure substances present?”-We can say yes if we can list at least 2 pure substancesSolid Liquid Gas Atom/Molecular level Close packing Close packing Separated by long distances NOT move around move around fly around Macroscopic level Incompressible Incompressible compressible Fixed volume Fixed volume Assume the volume of the containerRigid shape Assume the shape of the container Assume the shape of the container The Scientific Approach to KnowledgeObservations: Natural phenomena and measured events; Universally consistent ones → natural laws. Hypothesis: Tentative proposal that explains observations. Experiment: Procedure to test hypothesis; measures one variable at a time. Model (Theory): Consistent explanation data from accumulated experiments; Predicts related phenomena. Further Experiment: Tests predictions based on model 3 Natural Laws of Matter: keystone to ChemistryWe often take these laws for granted; we use them everyday- Law of conservation of matter (Antoine and Marie Lavoisier 1775): matter does not change when there is a chemical reaction- Law of constant composition (law of definite proportion- Joseph Louis Proust 1797) A pure chemical substance always contains the same proportions of elements by mass, no matter the source.- Law of multiple proportions (John Dalton 1808) when two elements form two different compounds, the masses can be expressed as a ratio of small whole