With Dr. Wieser

 Chemistry can be defined as the study of matter.  Matter is anything that has mass and occupies space. So chemistry is the study of pretty much everything.  We will focus on the structure of matter and the changes that matter can undergo.

 A chemical is defined as any substance that has a definite composition.  Look around the room-how many chemicals can you observe?  There are many different branches of Chemistry. See p4.  Also on PP4-5-different types of research are discussed.

 We can define matter as anything that has mass and occupies space. All matter is composed of atoms. Elements and compounds are made up of atoms.  An atom is the smallest unit of an element that has the properties of that element. An element is a pure substance and can not be broken down into simpler substances.

 A compound is a pure substance that is made of two or more elements that can be broken down into simpler substances.

 Matter can exist in four states (three are found on Earth)  Solid  Liquid  Gas  Plasma (found in the interior of the sun)

 Note that energy must be supplied to go from one state or phase to another:  Solid →liquid→gas  Solids-have fixed volume and shape.  Liquids-have fixed volume but take on the shape of their container.  Gases-have neither fixed volume or shape.

 In addition to phase changes matter can undergo other physical changes:  Physical changes do not produce any new substances:  What happens to an ice cube when heat is supplied?  What about when sugar is dissolved in water?

 Chemical changes produce new substances.  In a chemical reaction one or more substances, the reactants are converted to one or more new substances, the products.

 A physical property is one that describes a physical change. When considering phase changes, the melting point of a substance is a physical property. In the case of ice, this temperature is______ o C.  A chemical property describes the chemical change. Paper undergoes a chemical change when it burns, so the ability to react with oxygen is a chemical property of paper.

 Compounds and elements are both pure substances.  Compounds are a chemical combination of two or more elements.  Mixtures are a physical combination of two or more pure substances.  Mixtures that are uniform in composition are called homogenous mixtures (sugar in water)  Mixtures that are not uniform are heterogeneous mixtures (sand in water)

 Homework: always due at the beginning of the next class period.  P 14 #’s  And p22 #’s 10-12

 I mentioned previously that elements are composed of atoms. The periodic table lists all the known chemical elements.  The columns are called groups or families – there are 18 of them.  The rows are called periods. (see p 17).  There are three types of elements shown on the table.

 Metals  Non-metals  Metaloids or semi-metals  Pages give examples.  Homework for section 3  Page 20 #’s 1-4  END of Chapter 1 a test will follow.

15  Observation  Hypothesis  Observation or experiment  Theory  Observation or experiment  Law  See page 31

 Scientists ask questions and make observations.  A hypothesis is a possible explanation for an observation. A hypothesis must be testable- usually by performing an experiment and analyzing the result.

 Experiments are conducted under controlled conditions.  If the results of an experiment may support the hypothesis- which will lead to more experiments or not support it-then you need to look for a new hypothesis or the result may lead you in a whole new direction.  If over a relatively long period of time many experiments support the hypothesis then the hypothesis can become a theory.

 A theory is the best current explanation for a series of observations. If new information becomes available in the future then the theory may be modified or even replaced. This is all part of the scientific method!  In the course of performing experiments, sometimes a cause and effect relationship is observed. 

 This relationship is a scientific law-scientific laws do not explain observations but point out connections between observations. For example later in the year we will study the Gas Laws-one says that when the temperature of a gas goes up so does its volume-the theory that explains this observation is called the Kinetic Theory of gases.

 One of the key parts of the scientific method is the ability to make measurements.  If I told you a measurement was What would be your response?

 The metric system is the one used in science. The units are called SI units-we will see that not all the units we will use are SI units.  SI base units are listed on p 34.

 Some for you to try:  a g to kg  b cm to m  c mg to kg

 Derived units: many measurements use more complicated units derived from the base units. For example volume (l x w x h) requires a cubic unit, if the measurements were in meters the unit would be m 3.  The non-SI unit we commonly use for volume is the liter which is equivalent to a dm 3 or 1000 cm 3 (1000 mL)

 One important physical property of matter is density.  Density = mass/volume  Every substance has its own unique density.  See p 17 for a list.  Since the density formula has 3 variables, 3 types of problems are possible.

 1. given mass and volume-find density  a substance has a mass of 23.2 grams and a volume of 18.5 cm 3. Find its density.  2. given density and volume, find mass (g)  D = m/V so m=D x V  The density of silver is 10.5 g/cm 3. Find the mass of a block of silver with a volume of 40.0cm 3.

 3. Given the density and mass, find the volume of a substance.  D= m/V so V= m/D  Find the volume of a piece of iron that has a mass of 147grams. (from p 17 density of iron = 7.86 g/cm 3 )

 Substances (pure)  - matter in which all samples have identical composition and properties.  Elements ◦ substances that cannot be decomposed into simpler substances via chemical reactions  Elemental symbols ◦ found on periodic chart 27

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 Compounds ◦ substances composed of two or more elements in a definite ratio by mass ◦ can be decomposed into the constituent elements  Water is a compound that can be decomposed into simpler substances – hydrogen and oxygen 29

 The properties(chemical and physical) of compounds are unique and are totally different from the elements that make up the compound.  Sodium chloride for example.  NaCl

 Mixtures ◦ composed of two or more substances ◦ homogeneous mixtures ◦ heterogeneous mixtures 31