Chapter 1 Matter Measurement and Problem Solving 1 1 Atoms and Molecules Atoms are the submicroscopic particles that constitute the fundamental building blocks of ordinary matter They are most often found in molecules Molecules are two or more atoms joined in a specific geometrical arrangement Chemistry is the science that seeks to understand the behavior of matter by studying the behavior of atoms and molecules 1 2 The Scientific Approach to Knowledge Qualitative experiments describe how a process happens Quantitative experiments measure something about the process A hypothesis is a tentative interpretation or explanation of the observations in an experiment o A good hypothesis is falsifiable Hypotheses are tested by experiments which are highly controlled procedures designed to generate such observations Scientific Law is a brief statement that summarizes past observations and predicts future ones o Scientific laws describe how nature behaves they are generalizations about what nature does For this reason they are also referred to as scientific principles One or more well established hypotheses may form the basis for a scientific theory which is a model for the way nature is and tries to explain not merely what nature does but why Matter is anything that occupies space and mass o We can classify matter according to its state solid liquid or gas and according to its 1 3 The Classification of Matter composition The State of Matter Solid Liquid and Gas In solid matter atoms or molecules pack close to each other in fixed locations Although the atoms and molecules in a solid vibrate they do not move around or past each other o A solid has a fixed volume and rigid shape o May be arranged in two ways Crystalline in which case its atoms or molecules are arranged in patterns with long range repeating order Amorphous in which case its atoms or molecules do not have any long range order In liquid matter atoms and molecules pack about as closely as they do in solid matter but they are free to move relative to each other o Liquids have a fixed volume but not a fixed shape In gaseous matter atoms or molecules have a lot of space between them and are free to move relative to one another o Gaseous matter is compressible o They have no fixed volume nor shape they spread to fill their container Classifying Matter According to Its Composition Elements Compounds and Mixtures The first division in the classification of matter depends on whether or not the composition can vary from one sample to another o A Pure Substance is one composed of only a single type of atom or molecule Can be divided into two types elements and compounds depending on whether or not they can be broken down into simpler substances Element A substance that cannot be chemically broken down into simpler substances Compound A substance composed of two or more elements in fixed definite proportions o Heterogeneous Mixture One in which the composition varies from one region to another o Homogeneous Mixture One with the same composition throughout o A Mixture is a substance composed of two or more different types of atoms or molecules that can be combined in variable proportions Separating Mixtures In general mixtures are separable because the different components have different physical or chemical properties Decanting Carefully pouring off container o Ex A mixture of sand and water where the water is carefully poured off into another Distillation A process in which the mixture is heated to boil off the more volatile easily vaporizable liquid which is then re condensed in a condenser and collected in a separate flask Filtration A mixture is poured through filter paper usually held in a funnel 1 4 Physical and Chemical Changes and Physical and Chemical Properties Physical Changes Changes that alter only state or appearance but not composition o The atoms of molecules that compose a substance do not change their identity during a Ex water boiling because from liquid to gas they are still water molecules Chemical Changes Changes that alter the composition of matter o During a chemical change atoms rearrange transforming the original substances into physical change different substances Ex Iron rusting because the iron atoms combine with oxygen molecules from air to form iron oxide Physical Property One that a substance displays without changing its composition o Ex odor taste color appearance melting point boiling point and density Chemical Property One that a substance displays only by changing its composition via a chemical change o Ex corrosiveness flammability acidity and toxicity The differences between physical and chemical changes are not always apparent Only chemical examination can confirm whether any particular change is physical or chemical 1 5 Energy A Fundamental Part of Physical and Chemical Change Energy The capacity to do work Work The action of a force through a distance The Total Energy of an object is a sum of its o Kinetic Energy The energy associated with its motion o Potential Energy The energy associated with its position of composition Thermal Energy The energy associated with the temperature of an object o A type of kinetic energy because it arises from the motion of the individual atoms or molecules that make up an object Law of Conservation of Mass ENERGY IS NEITHER CREATED NOR DESTROYED o The potential energy becomes kinetic energy which becomes thermal energy o There is a tendency of systems with high potential energy to change in a way that lowers their potential energy Objects or systems with high potential energy tend to be unstable Chemical potential energy such as that contained in the molecules that compose gasoline arises primarily from electrostatic forces between the electrically charged particles protons and electrons that compose atoms and molecules 1 6 The Units of Measurement Units Standard quantities used to specify measurements The Standard Units Quantity Length Mass Time Temperature Amount of Substance Electric Current Luminous Intensity Unit Meter Kilogram Second Kelvin Mole Ampere Candela Symbol m kg S K Mol A cd The Meter A Measure of Length Meter 39 37 inches slightly longer than a yard 36 inches The Kilogram A Measure of Mass Kilogram kg Mass of a metal cylinder kept at International Bureau of Weights and Measures at Sevres France Measure of mass a quantity different from weight o Mass A measure of the quantity of matter within is o Weight A measure of the gravitational pull on the
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