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Chem Com Unit 1A

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

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Chem Com Unit 1A

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  1. Chem Com Unit 1A Building blocks of chemistry

  2. 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

  3. 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

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

  5. 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? • Is there a change in the identity of the wood and oxygen? • If no, then the statement describes a physical property • If yes, then the statement describes a chemical property • The ash left over from a campfire looks nothing like the original wood that was burned • The reaction products of ash, carbon dioxide, and water vapor are very different from wood and oxygen.

  6. 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

  7. 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 • NH3 – ammonia • C12H22O11 – sugar

  8. 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 3rd type of bond which only occurs among metals • Metallic bond

  9. 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 = Beryllium Au = gold (aurum)

  10. 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. NH3 – one nitrogen (N) atom and three hydrogen (H) atoms

  11. 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 H2 + N2 2 NH3 Hydrogen nitrogen ammonia reactants products 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

  12. Sample problems • The chemical formula for propane, a compound commonly used as a fuel, is C3H8. 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. P d. Co g. Na • b. Ni e. Br h. Fe • c. Cu f. K

  13. 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)

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