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FRESHMAN CHEMISTRY 124, Handout 1: Chapter 1 Definitions
1.2 METHODS OF SCIENCE
A HYPOTHESIS is a tentative explanation of an observation. A LAW is a concise verbal or mathematical statement of a relationship. A THEORY is a unifying principle that explains known facts and allows prediction of new facts. QUANTITATIVE information is numerical. T = 76 C P = 1.6 atm QUALITATIVE information is descriptive such as "red", "large crystals".1.3. SOME DEFINITIONS
MATTER is anything that occupies space and has mass (what is difference between mass and gravity?) MATTER exists in the three phases. A SOLID is material where particles are arranged into definite, rigid shape, very little change with T, P. A LIQUID has a definite volume - takes the shape of its container - small change with T, P (does not compress much). A GAS has neither a fixed volume nor shape, easily compresses, expands by T, P. ATOMS are the smallest particles of an element that retain the chemical properties. AN ELEMENT is matter that consists of only one kind of atom (simplest type of material). MOLECULES are units of matter consisting of two or more atoms combined in a definite ratio. H2O = water A COMPOUND is a collection of molecules. A SUBSTANCE is a form of a compound. H2O = ice water, steam A MIXTURE is 2 or more substances. A HOMOGENEOUS mixture has the same composition throughout. NaCl + H2O --> salt water. A SOLUTION consists of a homogeneous mixture of 2 or more substances. "a solute (NaCl,sugar) dissolved in a solvent (H2O, H2O). A HETEROGENEOUS mixture is a mixture that can be observed as individual substances. salt & sand, students in a room (In either a homogeneous or a heterogeneous mixture the components can be separated by physical means.) PHYSICAL PROPERTIES can be measured and observed without changing the atom ratios of a substance such as mp, bp, color, density, physical state, etc. CHEMICAL PROPERTIES occur when there is a change in atom arrangements or atom ratios. O2 CH4--- --------> CO2 + H2O (combustion) O2 Fe --------------> Fe2O3 (rust, oxidation) EXTENSIVE PROPERTIES depend on the amount of material present e.g., volume, mass. INTENSIVE PROPERTIES are the same regardless of sample size mp, bp, color, (inherent to substances not its amount) - H2O mp = 0 C regardless of amount
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