Chemistry Chapter 1 1 1 The Study of Chemistry chemistry is the study of matter and the changes that matter undergoes matter is anything that has mass and occupies space molecules are made up of atoms smaller pieces of matter law a concise verbal or mathematical statement of reliable relationship between phenomena hypothesis a tentative explanation for their observations theory is a unifying principle that explains a body of experimental observations and the laws that are based on them observations hypothesis experiment theory further experiment scientific method 1 2 Classification of Matter matter can be classified as either a substance or a mixture of substances substance is a form of matter that has a definite constant composition and distinct proper ties such as color smell and taste all substances exist as a solid a liquid and a gas the three physical states in a solid particles are held close together with little free motion does not conform to the shape of its container in a liquid particles are close together not held rigidly together and free to move past one another and conforms to the shape of the part of the container it fills in a gas the particles are separated by distances that are very large a sample of gas as sumes both the shape and the volume of its container we can convert a substance from one state to another without changing the identity of the mixture is a combination of two or more substances in which each substance in which each substance retains its distinct identity mixtures can be solids liquids or gases Ex trail mix sterling silver apple juice sea mixtures do not have a universal constant composition mixtures are either homogenous or heterogenous substance water homogenous mixture the composition of the mixture is uniform throughout Ex dis solved sugar in water heterogenous mixture the composition of the mixture is not uniform Ex sand with fill ings a mixture can be separated into the substances it contains without changing the identities of the individual substances the processes used to separate mixtures are called physical processes physical process is one that does not change the identity of any substance Ex filtration distillation 1 3 The Properties of Matter Properties of a substance may be quantitative or qualitative quantitative measured and expressed with a number qualitative not requiring explicit measurement physical properties is one that can be observed and measured without changing the iden tity of a substance Ex color melting point boiling point and physical state physical change one in which the state of matter changes but the identity of the matter does not change Ex melting chemical property any property of a substance that cannot be studied without converting the substance into some other substance chemical change a process in which one or more substances are changed into one or more new substances Ex is corrosion or oxidation of iron after a chemical change the original substance no longer exists Ex baking cookies all properties of matter are either extensive or intensive extensive property depends on the amount of matter Mass is an extensive property Can add subtract intensive property does not depend on the amount of matter Ex density and temperature 1 4 Scientific Measurement pressed using numbers properties that can be measured are called quantitative properties because they are ex two systems of unit english system metric system revised metric system is called the International System of Units SI Units mass is a measure of the amount of matter in an object or sample weight is the force exerted by an object or sample due to gravity The weight of an object varies depending on where it is measured the mass of an object remains the same regardless of where it is measured Base SI Units Length meter m mass kilogram kg time second s electric current ampere A temperature kelvin K amount of substance mole mol luminous intensity candela cd Prefixes Used with SI Units Tera 10 12 Giga 10 9 Mega 10 6 Kilo 10 3 Deci 10 1 Centi 10 2 Milli 10 3 Micro 10 6 Nano 10 9 Pico 10 12 atomic mass unit is used to express the masses of atoms and other objects of similar size angstrom a measure of length that is equal to 1 x 10 10 m two temperature scale used in chemistry the Celsius scale and the absolute of Kelvin scale Celsius scale freezing point 0 and the boiling point 100 K 273 15 Temperature in 9 5 x temperature in 32 density is the ratio of mass to volume 1 5 Uncertainty in Measurement significant figures are meaningful digits in a reported number 1 2 3 4 any digit that is not zero is significant zeroes located between nonzero digits are significant zeroes to the left of the first nonzero digits are not significant zeroes to the right of the last nonzero digit that does not contain a decimal point may or may not be significant Use scientific notation to avoid ambiguity in addition and subtraction the answer cannot have more digits to the right of the decimal point than any of the original numbers in multiplication and division the number of significant figures in the final product or quotient is determined by the original number that has the smallest number of significant fig ures accuracy tell us how close a measurement is to the true value precision tells us how close a series of replicate measurements measurements of the same thing are to one another 1 6 Using Units and Solving Problems conversion factor is a fraction in which the same quantity is expressed one way in the nu merator and another way in the denominator dimensional analysis is a series of unit conversions used in the solution of a multistep problem