Unit 2-Chemical Bonds & Solution Chemistry Textbook Ch.6-9 (p.174-323)

Why are atoms compared to Legos? They can combine in different ways to form different compounds and molecules.

Chemical Bonds Chemical Bond – the force that holds atoms or ions together in a compound In a reaction, bonds are broken and rearranged

Chemical Structure Chemical Structure – the arrangement of atoms in a substance Structure determines properties e.g., state of matter, melting and boiling points

Compounds & Molecules Compound – A substance made up of atoms of 2 or more different elements joined by chemical bonds Molecule – A group of atoms that are held together by chemical forces e.g., Water is a compound because it is made up of two different elements (H and O) and a single molecule of water contains 2 hydrogen atoms and 1 oxygen atom (H2O)

Why do bonds form? Atoms join to form bonds so that each atom has a stable electron configuration (full outer level).

Types of Bonds Ionic Bond – The attractive force between oppositely charged ions

Types of Bonds Covalent Bond – A bond formed when atoms share one or more pairs of electrons

Types of Bonds Differences Between Ionic & Covalent Bonds Ionic Compounds Covalent Compounds Structure network of bonded ions molecules Valence Electrons transferred shared Electrical Conductivity good (when melted or dissolved) poor State at Room Temperature solid solid, liquid, or gas Melting & Boiling Points generally high generally low Usually between metals / nonmetals nonmetals

Types of Bonds Metallic Bond – A bond formed by the attraction between positively charged ions and the electrons around them.

Polyatomic Ions Polyatomic Ion – An ion made of two or more atoms Parenthesis group the atoms

TEXTBOOK SECTION ASSIGNMENT: Read {6.1 & 6.2 p.177-190 Complete p.182 Q’s 1, 3-5 and p.190 Q’s 1, 3, 5, 6, 7, 9

Chemical Reactions Physical Change -A change that alters the form of a substance but not the chemical makeup of the substance, a change of state Words like: crush, smash, tear, evaporate, slice, dissolve, absorb, swell, burst

Chemical Reactions Chemical Change - One or more substances combine or decompose to form a chemically different substance Words like: react, burns, forms, decomposed, rusting, sours, rotting, digesting, cooked, molecular change Another word for a chemical change is a chemical reaction

Chemical Reactions Chemical reactions occur when chemical bonds are formed or broken Strong chemical bonds resist change: glass Weak chemical bonds breakdown easily: wood Why do chemical reactions occur? Atoms become more stable when they bond.

Chemical Reactions Chemical reactions produce new substances that can usually be detected by observing the evidence: Color change Precipitation Temperature change Property change Gas produced

Structure of a Chemical Equation Law of Conservation of Mass - Matter cannot be created nor destroyed so there must be the same number of atoms on each side of the equation Beginning materials are reactants Ending materials are products

Structure of a Chemical Equation Coefficient – a whole number in front of an element or molecule in a chemical reaction Tells how many of each element or molecule is present

Structure of a Chemical Equation Be careful!!! Do not confuse coefficients with subscripts!

Structure of a Chemical Equation Remember... Chemical formulas show the ratio of elements found in molecules and compounds Subscripts: If no subscript present it is assumed to be 1 atom If elements in brackets or parenthesis, treat same as in math.

Structure of a Chemical Equation Coefficients: Coefficients multiply the entire molecule’s atoms CaCl2 Ca=1 Cl=2 Ca3(PO4)2 Ca=3 P=2 O=8 2Ca3(PO4)2 Ca=6 P=4 O=16

Structure of a Chemical Equation To satisfy the Law of COM, you must add all reactant molecules together & compare with all molecules in the products The # of reactant atoms must equal the # of product atoms

Energy & Chemical Reactions Chemical reactions can be categorized by the way energy flows into and out of the process

Energy & Chemical Reactions Exothermic Reactions: Heat is RELEASED. Products will have less potential energy than reactants. Examples: Burning wood in a fire makes smoke and ash that has less stored energy than the wood. It releases heat and light energy Reactants  Products + Energy

Energy & Chemical Reactions Endothermic Reactions: Heat is ABSORBED. Thermal energy gets stored in the chemical bonds – the products will have more potential energy than the reactants. Examples: Frying an egg; decomposing H2O; instant cold packs Reactants + Energy  Products

Classifying Reactions There are millions of possible reactions ...however, there are only a few general kinds of reactions Patterns can be used to identify kinds of chemical reactions and to predict products of these reactions

Synthesis Reaction Definition: Reaction in which two or more substances combine to form a new compound General Form: A + B  AB Example: 2 Na + Cl2  2NaCl

Decomposition Reaction Definition: Reaction in which a single compound breaks down to form two or more simpler substances General Form: AB  A + B Example: 2H2O  2H2 + O2

Single-Displacement Reaction Definition: Reaction in which one element takes the place of another element in a compound In general, the more reactive element will take the place of the less reactive one General Form: AX + B  A + BX Example: 3CuCl2 + 2Al  2AlCl3 + 3Cu

Double-Displacement Reaction Definition: Reaction in which a gas, a solid precipitate, or a molecular compound forms from the apparent exchange of atoms (or ions) between two compounds General Form: AX + BY  AY + BX Example: Pb(NO3)2 + K2CrO4  PbCrO4 + 2KNO3

Combustion Reaction Definition: The oxidation reaction of an organic compound in which heat is released. Oxygen is always a reactant organic compound – contains carbon Example: CH4 + O2  CO2 + 2H2O

Oxidation-Reduction (“REDOX”) Reaction Definition: Any chemical change in which one species is oxidized (loses electrons) and the other species is reduced (gains electrons) Example: 4Fe + 3O2  2Fe2O3 **Each Fe loses 3 electrons to form Fe+3 ions while each O2 gains 2 electrons to form O2- ions

Rates of Reaction Reaction Rate: how fast a chemical reaction takes place Collision Theory: Rate of the reaction depends on the frequency of the collisions between atoms Anything that increases the contact between particles increases reaction rate. (Anything that decreases contact slows the rate.)

Factors Affecting Reaction Rate There are six major factors that affect the number of collisions of particles in a reaction. Concentration Surface area Temperature Pressure Molecular size Catalysts

Factors Affecting Reaction Rate Concentration – the greater the concentration of reactants, the faster the reaction rate Example: Using a concentrated bleach will bleach clothes faster than a diluted bleach

Factors Affecting Reaction Rate Surface Area – the more surface area in contact between the reactants, the more atoms can interact, so the faster the reaction goes Example: Sawdust burns faster than a log

Factors Affecting Reaction Rate Temperature– the higher the temperature, the faster the atoms are moving, the more collisions they have, making the reaction occur at a faster rate Example: Rusting of iron happens faster at a higher temperature

Factors Affecting Reaction Rate Pressure–Putting reactants under higher pressure will force more atoms together harder….so the reaction rate will increase. Example: The piston in your car compresses the gas-air mixture before it burns.

Factors Affecting Reaction Rate Molecular Size-Big molecules are slower, they have fewer collisions, and therefore they react slower. Example: Sugar burns slower than hydrogen

Factors Affecting Reaction Rate Catalysts-Substances that do not enter into the chemical reaction but encourage collisions. Example: Catalytic converters-catalysts of platinum, palladium, and rhodium in cars; Enzymes-proteins in the body “Reverse catalysts” (inhibitors)-Substances that slow down reactions

TEXTBOOK SECTION ASSIGNMENT: This assignment will be checked next class: Read {7.1, 7.2 & 7.4 p.219-227, p. 238-241 in textbook Complete the following practice problems p.224 Q’s 1-5 p.229 Q’s 1-3 p.247 Q’s 1-3, p.253 Q 19