CHEM COM UNIT 1A BUILDING BLOCKS OF CHEMISTRY

PROPERTIES  Properties that can be determined without altering the chemical make-up of a substance  Physical  Color  Density  Odor  Properties that are determined only when a substance has undergone a change into one or more substances  Chemical  Rusting  Formation of a solid or gas  Temperature change

CHANGES Physical change The material remains the same, even though its form seems to have changed Chemical change The material has changed into one or more new substances May be accompanied by physical changes as well

SAMPLE PROBLEM 1: Consider this statement: Substances containing copper are often blue in color. Does this statement describe a physical or chemical property? 1.Was the substance chemically changed for its color to be observed? 1.If no, then the statement describes a physical property 2.If yes, then the statement describes a chemical property

SAMPLE PROBLEM 2: Consider this statement: Oxygen gas supports the burning of wood. Does this statement describe a physical or chemical property of oxygen gas? 1.Is there a change in the identity of the wood and oxygen? 1.If no, then the statement describes a physical property 2.If yes, then the statement describes a chemical property 2.The ash left over from a campfire looks nothing like the original wood that was burned 3.The reaction products of ash, carbon dioxide, and water vapor are very different from wood and oxygen.

THE PARTICULATE VIEW OF MATTER Particulate level – the level of atoms and molecules Matter – anything that occupies space and mass Atoms – the “building blocks” of matter Element – matter that is made up of only one type of atom Approximately 90 different elements found in nature Between 110 and 115 elements found on the periodic table Each has its own identifying properties

Compound - a substance composed of atoms of two or more elements linked together chemically Linked in fixed proportions More than 30 million compounds have been identified Can be represented by chemical formulas NaCl – table salt NH 3 – ammonia C 12 H 22 O 11 – sugar

Molecule – smallest unit of a molecular compound Atoms in a molecule are held together by chemical bonds These bonds fall into two major categories, Ionic Covalent There is a 3 rd type of bond which only occurs among metals Metallic bond

SYMBOLS, FORMULAS AND EQUATIONS Chemical symbols The “letters” of the chemical language Contain 1 or 2 letters The first letter is always capitalized If there is a second letter, it is lowercase Symbol comes from the element’s name, although not necessarily from the English name Ex.H = hydrogen;Be = BerylliumAu = gold (aurum)

Chemical formula – “words” in chemistry that represent different chemical compounds Subscript – the small number written below and to the right of a chemical symbol Represents the number of atoms of the preceding element can be found in that particular formula Ex.NH 3 – one nitrogen (N) atom and three hydrogen (H) atoms

Chemical equations – “sentences” of chemistry Summarizes the details of a particular chemical reaction, the breaking and forming of chemical bonds to produce new substances. Ex.3 H 2 +N 2  2 NH 3 Hydrogennitrogenammonia reactantsproducts Reactants – the original substances in a chemical reaction Products – the new substance(s) formed from the rearrangement of the reactants Balanced equation – the total number of atoms as reactants = the total number of atoms as products

SAMPLE PROBLEMS The chemical formula for propane, a compound commonly used as a fuel, is C 3 H 8. What elements are present in propane, and how many atoms of each are there in one molecule of propane? Use your yellow periodic table to name the elements represented by each of the following symbols: a.Pd.Cog.Na b.Nie.Brh.Fe c.Cuf.K

THE ELEMENTS Classification: Metals - found toward the left side of the periodic table Have properties such as malleability, luster, conductivity Examples include Fe (iron), Calcium (Ca) and Lead (Pb) Nonmetals – found toward the right side of the periodic table Have properties such as brittleness, dull and nonconductive Examples include S (sulfur), O (oxygen) and Br (bromine) Metalloids – found along the “stair-step” that divides metals from non-metals Have some properties of both metals and nonmetals Examples include Si (silicon) and As (arsenic)