Lecture 1 Chemistry 1211 Chapter 1 Matter and Measurement Chemistry the study of matter and energy it is a science that tries to understand the reactivity transformations properties structures and composition of atoms and molecules Observation an act or instance of viewing or noting a fact or occurrence for some scientific or other special purpose Law based on repeated experimental observations that describe some aspect of the world Hypothesis a supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation Theory a group of ideas to explain why something happens States of Matter Solids Rigid shape definite volume Atoms or molecules pack close together in fixed locations Although the atoms and molecules vibrate they do not move around or pass each other Consequently solids have fixed volume and rigid shape Solid matter may be crystalline solids or Amorphous solids Crystalline solids Atoms and molecules are in patterns with long in range repeating order Lecture 1 Amorphous solids Atoms and molecules do not have any long range order Liquids Takes shape of the container definite volume Pack about as closely as they do in solid matter but they are free to move relative to each other Has definite volume but no definite shape Assumes the shape of its container Gasses Atoms and molecules have a lot of space between them They are free to move relative to one another The qualities make gases compressible Classification of matter by substance Pure Substance Made up of only one component and its composition is invariant Categorized into 2 types Elements and Compounds Elements cannot be chemically broken down into smaller substances Compounds Substance composed of 2 or more elements in fixed definite proportions Mixture By contrast a substance composed of 2 or more components in proportions that can vary from one sample to another Mixtures can be categorized into Heterogeneous mixtures and Homogeneous mixtures Heterogeneous mixture One in which the composition varies from one region of the mixture to another Made or multiple substances whose presence can be seen Ex a salt and sand mixture Lecture 1 Portions of a sample of heterogeneous mixtures have different compositions and properties Homogeneous mixture One made of multiple substances but appears to be one substance All portions of a sample have the same composition and properties Ex sweetened tea Separating mixtures Mixtures are separable because of the different components have different physical and chemical properties Various techniques that exploit these differences are used to achieve separation 3 different ways of separation mixtures include Decanting Distillation and Filtration Decanting carefully pouring mixture into another container Ex sand and water Distillation Homogeneous mixture separating process Filtration Process in which a mixture is poured through filter paper in a funnel Physical and Chemical Changes Physical Change Changes that alter only the state or appearance but not the composition are physical changes the atoms or molecules that compose a substitute do not change their identity during a physical change Ex When water boils it changes its state from a liquid to a gas The gas remains composed of water molecules so this is a physical change Chemical Change Changes that alter the composition of matter are chemical changes During a chemical change atoms rearrange transforming the original substance into different substances Ex Rusting iron is a chemical change Physical and Chemical Properties Physical Properties Property that a substance displays without changing its composition Lecture 1 Ex smell of gasoline is a physical change Odor taste color appearance boiling point melting point are all physical properties Chemical Properties Property that a substance displays only by changing its composition via a chemical change or chemical reaction Ex The flammability of gasoline in contrast is a chemical property Chemical properties include corrosiveness acidity and toxicity Intensive and Extensive Properties Intensive properties properties whose value is independent of the quantity of matter Often used to identify the type of matter Ex Density boiling point melting point odor and color Extensive properties Properties whose properties cannot be used to identify what type of matter something is