Chemistry in the Community Mid Term Review Sections 0 through 1.D - PowerPoint PPT Presentation

Chemistry in the Community Mid Term Review Sections 0 through 1.D (p. 142 in the text book)

Section 0.C

0.3 Density of Solids and Liquids ¡ ¡M ¡ D ¡ ¡ ¡V ¡ • Density is a physical property D = , density of water = = 1 g/cm 3 mass 1 g volume 1 cm 3 • Calculate volume of a regular solid: Measure length x width x height (units: cm 3 , m 3 , ft 3 etc.) • Measure Volume of a liquid: Use a graduated cylinder: mL or L • Measure volume of an irregular solid by displacement with a graduated cylinder • Density of water = 1.00 g/mL 1 mL = 1 cm 3

Unit 1 Section A: Building Blocks of Chemistry

1.A.5 Molecular View of Matter • Matter – Anything that has mass and takes up space – All solids, liquids and gases are matter • Molecules are made of atoms held together by chemical bonds; eg. N 2 , H 2 O • Compounds are molecules with 2 or more different atoms; eg. H 2 O • Elements contain only one type of atom; eg. N 2 – there are ~115 elements; 88 naturally occurring – most occur as atoms, some as molecules – Diatomic elements: HONClBrIF

Unit 1 A.2 Physical and Chemical Properties • Physical properties- Properties that can be determined without altering the chemical makeup of the material. • Color, ductility, malleability, conductivity, density, odor, boiling point, melting point, Freezing point, and shape

Unit 1 A.2 Physical and Chemical Properties • Physical change in a substance does not involve a change in the identity of the substance (grinding, cutting, melting, and boiling) • These changes can usually be reversed (because the identity of the substance was not changed)

Unit 1 A.2 Physical and Chemical Properties • Chemical property relates to a substance ’ s ability to undergo changes that transform it into different substances. • Chemical change or Chemical reaction is a change in which one or more substances are converted into different substances.

Unit 1 A.2 Physical and Chemical Properties • A chemical change probably occurred if you observe one or more of the following: • Gas produced • Evolution of heat and light (Burning) • Formation of a precipitate • Change on the surface of a solid • Color Change to a new color that is not a result of the mixing of colors; Such as two clear substances yielding a red color.

Classify as chemical or physical change 1. You make scrambled eggs. 2. You step on a piece of chalk and it becomes powdered. 3. You light a match when the electricity goes out. 4. Steam from your hot shower condenses on a cold mirror. 5. Milk turns sour. 6. Wax melts. 7. Wax burns.

1.A.5 – Particles of Matter

Modeling Matter 1. Is an element or compound shown in a? 2. Two kinds of atoms are shown in b; is this a compound? 3. Which diagrams show only molecules? Compare them. 4. Which diagrams show mixtures? Compare them.

Symbols, Formulas, and Equations 1.A.6 • Chemical Symbols represent elements – First letter is capitalized; second letter is lower case • Chemical Formula represent different chemical substances, e.g. H 2 O – Subscript tells how many atoms of an element

Symbols, Formulas, and Equations 1.A.6 • Chemical Formulas are the “ words ” in the language of chemistry. • Chemical equations are the sentences. • Each chemical equation summarizes the details of a particular chemical reaction. • Chemical reactions entail the breaking and forming of chemical bonds. – Atoms are rearranged to from new substances. The properties of the new substances are different from those of the original material(s)

Chemical Equation for formation of water 2 H 2 + O 2 à 2 H 2 O Hydrogen Oxygen Water Reactants Product (Left side of the arrow) (Right side of the arrow)

Unit 1.A.9 The Chemical Elements Metals • Include such elements as iron, tin, zinc, and copper • At room temperature they are solids • A good conductor of heat and electricity • Malleability- hammered or rolled into sheets • Ductile- can be drawn in to a fine wire (high strength) • Luster- most metals have a grayish or silvery luster

Unit 1.A.9 The Chemical Elements Non Metals • Most are gases at room temperature (except bromine which is a liquid) • The solid nonmetals tend to be brittle • A poor conductor of heat or electricity

Unit 1.A.9 The Chemical Elements Metalloids- Such as Silicon and Germanium • Elements on the stair-step line that separate the metals from the nonmetals • Has some of the characteristics of metals and nonmetals • Are solids at room temperature • Less malleable than metals • Not as brittle as non-metals • Some have a metallic luster • Semiconductors of electricity (their ability to conduct electricity falls between that of metals and nonmetals)

Metals, Nonmetals, Metalloids

Unit 2 A.3 Lab: Metal or Non Metal? Mg (s) + HCl → MgCl 2 (aq) + H 2 (g) Zn (s) + HCl (aq) → ZnCl 2 (aq) + H 2 (g) Fe (s) + HCl (aq) → FeCl 3 (aq) + H 2 (g) Sn (s) + HCl (aq) → SnCl 2 (aq) + H 2 (g)

How do you select a material for a specific use? • Need suitable physical and chemical properties • Need suitable cost Examples: • during WWII (1943), pennies were made of steel, but they corroded • Post 1982 pennies have a zinc core (cheaper) – 97.5% Zinc

Unit 1 Section B: Periodic Trends

Periodic Table Origins 1.B.2 • By mid-1800s, about 60 elements known; mostly solids. • 1869 Dmitri Mendeleev published a periodic table with elements in a regular pattern – Elements arranged horizontally in order of increasing atomic weight (relative mass of individual atoms) – Elements with similar “ combining capacity ” for oxygen and chlorine placed in vertical groups (columns)

1.B.3 Electrical Nature of Matter • Demonstrate charged balloon • Like charges repel - - + + • Unlike charges attract + -

1.B.3 Electrical nature of Matter • These Positive and negative charges in an atom are: • Protons --positive charge • Electrons --negative charge • Neutrons -- neutral charge • The attraction between these particles are the “ glue ” that hold the atom together

The Pattern of Atomic Numbers 1.B.4 • Properties of elements depend mostly on the elements ’ electronic structures. • Electronic structure- The arrangement of electrons in the atom of an element. • Number of electrons is the same as the number of protons for an electrically neutral atom. (not for ions)

The Pattern of Atomic Numbers 1.B.4 • The atomic number (# of protons) identifies an element – Every atom of carbon contains 6 protons in the nucleus • The nucleus also contains neutrons, which have about the same mass as protons – The mass # of an atom = #protons+#neutrons – Electrons have 1/2000 the mass of a proton, don ’ t contribute to mass # – Carbon atoms can have 6, 7, or 8 neutrons • Isotopes = atoms with same # protons, different # neutrons • Mass Number

Average Atomic Mass 1.B.4 Why is the atomic mass of chlorine (35.5 g) not a whole number? Chlorine has two isotopes 76% of Cl = 35 Cl (17 protons + 18 neutrons) = 35 g/mol 24% of Cl = 37 Cl (17 protons + 20 neutrons) = 37 g/mol weighted average = closer to 35 g/mol = (0.76 x 35 g/mol) + (0.24 x 37 g/mol) = 35.5 g/mol

The Periodic Table 1 Group 2 3 4 5 6 7 Periods ¡ ¡ Groups ¡ ¡

Unit 1.B.7 Organization of the Periodic Table Groups or Families • Vertical columns of the periodic table • Each group contains elements with similar properties

Unit 1.B.7 The Periodic Table Periods • Horizontal rows • Elements close to each other have more similar properties than those further apart

Unit 1.B.7 The Periodic Table Noble Gases • Unreactive or Inert elements

Unit 1.B.7 The Periodic Table Halogens • Elements of group 17 • F, Cl are gases at room temperature • Br is a reddish liquid • I is a dark purple solid • At is a solid • Most reactive of the nonmetals

Unit 1.B.7 The Periodic Table Alkali Metals • The elements of group 1 on the periodic table • Silvery appearance • Soft enough to cut with a knife • Very reactive (usually stored in kerosene because of their reactivity with air or moisture)

Unit 1.B.7 The Periodic Table Alkaline Earth Metals • Elements in group two • Harder denser stronger than alkali metals • Less reactive than alkali metals • Too reactive to be found in nature as free elements

Unit 1.B.7 The Periodic Table Exceptions to the rule: • Hydrogen(H) even though it ’ s part of group 1, does not share the same properties of group 1

Unit 1.B.7 The Periodic Table Transition elements • Metals with metallic properties • Good conductors of electricity and have high luster • Less reactive than alkali and alkaline earth metals • Do not easily form compounds • Exist in nature as free elements

Unit 1.B.7 The Periodic Table Inner Transition Elements • All metals • Lanthanides – Shiny metals • Actinides – All radioactive – All beyond uranium are synthetic

Unit 1.B.7 The Periodic Table Main Group Elements • Groups 1-2 • Groups 13-18