Atoms Chemistry 131 Chapter 1 The properties of matter are determined by the structure of the atoms and molecules that compose them 1 1 A Particulate View of the World Structure Determines Properties Two Main Points of chemistry Matter is particulate it is composed of particles The structure of those particles determines properties of matter Matter is anything that occupies space and has mass Atoms are the basic particles that compose ordinary matter When atoms bind together in specific geometrical arrangements they form molecules Chemistry is the science that seeks to understand the properties of matter by studying the structure of particles that compose it 1 2 Classifying Matter A Particulate View Substance is a specific instance of matter air water sand The state of matter is the first classification Depends on the relative position of particles and how strongly they interact with one another The composition of matter is the second classification Depends on the type of particles States of Matter Fixed Volume Fixed Shape Solid particles are fixed in place and can only vibrate Liquid particles are closely packed but can move past each other allowing liquid to flow and take shape of container Gas particles are widely spaced making gas compressible as well as fluid Compositions of Matter Pure Substance Made up of one type of particle one component Composition is invariant does not vary Individual atoms or groups of atoms joined together Ex helium He water H 2O sodium chloride NaCl Element a substance that cannot be chemically broken down into simpler substances Helium He Compound a substance composed of two or more elements in fixed definite proportions Water H 2O Most Common Mixture Made up of two or more particles Composition can vary from one sample to another Ex sweet tea can have a lot of sugar or a little Fixed Volume No Fixed Shape No Fixed Volume No Fixed Shape Heterogeneous the composition varies from one region of the mixture to another water sand does not mix uniformly Homogeneous the composition is the same throughout the mixture sweet tea mixes uniformly Matter Pure Substance Mixture Element Compound Heterogeneous Homogeneous Helium Particles are atoms Water Particles are molecules Wet sand two types of particles Tea w sugar two types of particles that can be distinctly separated that mix thoroughly together 1 3 The Scientific Approach to Knowledge Based on observation and experiment Can be qualitative noting describing how a process happens or quantitative measuring or quantifying something about the process Hypothesis Experiments Scientific Law Scientific Laws describe how nature behaves generalizations about what nature does Scientific Theory a model for the way nature is and why Most scientific observations are quantifiable and use units A unit is a standard quantity by which to measure Metric system English system International System of Units SI SI Base Units Quantity Length Mass Time Temperature Amount of Substance Electric Current Luminous Intensity Unit Meter Kilogram Second Kelvin Mole Ampere Candela 1 4 Early Ideas about the Building Blocks of Matter Leucippus Democritus Symbol M kg s K mol A cd Many different kinds of atoms existed in different shapes and sizes Matter has no smallest part and different substances are composed of fire air earth and water Plato Aristotle Copernicus The sun is the center of the universe scientific revolution 1 5 Modern Atomic Theory and the Laws That Led to It Dalton s theory that all matter is composted of atoms grew out of observations and laws The most important laws led to the development acceptance of atomic theory 1 The Law of Conservation of Mass In a chemical reaction matter is neither created nor destroyed Chemical reaction process in which one or more substances are converted into one or more different substances S 32g Fe FeS 56 88g g Mass of reactants Mass of products 2 The Law of Definite Proportions elements by mass in any size A chemical compound always contains exactly the same proportion of Mass ratio 16g of O 2gof H 8 0 or 8 1 3 The Law of Multiple Proportions If two elements A B form more than one compound the mass of B combined with 1g of A will be a ratio of a whole number Carbon Dioxide Carbon Monoxide 1g carbon 2 67g oxygen 1g carbon 1 33g oxygen oxygen carbon carbon dioxide oxygen carbon carbonmonoxide 2 67 1 33 2 John Daltons Atomic Theory 1 Each element is composed of tiny indestructible particles atoms 2 All atoms of a given element have the same mass properties different to atoms of other elements 3 Atoms combine in simple whole number ratios to form compounds 4 Atoms of one element cannot chance into atoms of another element In chemical reaction atoms only change the way they are bound together with other atoms Measurements of the relative weights of matter samples 1 before after reaction 2 different samples of the same compound and 3 different compounds composed of same elements indicated that matter is particulate 1 6 The Discovery of the Electron All matter is composed of atoms but atoms are composed of even smaller particles Discovered Electron Cathode Rays JJ Thompson Particles that compose the Cathode Ray travel in straight lines Independent of composition they originate from Cathode Carry negative electric charge Electron a negatively charged low mass particle present within all atoms Deduced charge of single electron Oil Drop Experiment Robert Millikan 1 60 x 10 19 C charge of 1 single electron 9 10 x 10 28g mass of 1 single electron 1 7 The Structure of the Atom Electron Plum Pudding Model Thompson Sphere of Positive Charge Radioactivity emission of small energetic particles from the core of certain unstable atoms Allowed researchers to experimentally probe the structure of the atom alpha particles positively charged most massive beta particles gamma particles Proton The Nuclear Atom Rutherford Nuclear Theory Neutron 1 Most of the atoms mass all of its charge are in the nucleus contains 99 of mass but very little volume 2 Most of the volume of the atom is empty space where charge electrons are dispersed 3 There are as many charged electrons outside the nucleus as there are charged protons inside the nucleus The atom also includes neutrons neutral particles within the nucleus Neutrons weigh the same as protons Matter is mostly empty space but appears solid because the variation in its density is on a scale too small for our eyes to see 1 8 Subatomic Particles Protons Neutrons and