General Science– Chemical Reactions Chapter 3 Characteristics of Compounds How Cmpds are Formed Chemical Formulas What is a Reaction? Using Chemical Equations

Lesson 3.1: Characteristics of Cmpds Chemical vs Physical changes: Chemical changes produce new substances with new properties. Evidence of chemical rxns: combustion (burning), gas (bubbles) form, * heat released or absorbed (gets hot or cold/change in temp), * color changes, light or sound given off, a solid (precipitate) formed. * Video of this evidence…… Most Imptnt Chem Rxns of History

Physical Changes Characteristics of Compounds: Change the appearance of a substance but do not change it into another substance. Include mixing, dissolving, melting, freezing, evaporation, etc. Characteristics of Compounds: One type of cmpnd ALWAYS contains the same elements. These elements always found in the same ratio within 1 molecule. (ie. H2O vs H2O2 or CO vs CO2)

Lesson 3.1b Periodic Table Trends A row on the table is called a period. Each column is called a family. Each family has similar chemical properties.

Periodic Table Trends (cont)

Metals and Nonmetals Valence electrons are the OUTERMOST elections & involved in chemical reactions. Determines the chemical properties of the element. Elements that have 1 to 3 valence electrons have metallic properties and are called metals. Elements that have 4 to 7 valence electrons are called nonmetals. Watch this on metals & nonmetals (VIDEO) then fill in the chart

Atoms don’t react, Ions do An ion is an atom that has an unequal number of protons and electrons. The atom has lost or gained electrons thus becoming either positive (less e-) or negative (more e-). Each atom wants enough electrons to have a full outer energy shell. Only element family that’s stable is #18 – noble gases - they don’t react. Ions in Group or Families 1-17 either lose or gain or share e- in order to become more stable, forming cmpds when they do so.

How Compounds are Formed Electrons are KEY Each family needs to lose or gain e- to be stable Families w/+ oxidation states lose e-. Families w/- oxidation states gain e-.

Lesson 3.2: Types of Bonds in Cmpds Giving/Losing electrons to form cmpds: Chemical Bonds are the force of attraction between charged ions Ionic bonds form when e- transfer between atoms forming ions. These usually form between a metal & a nonmetal.

Types of Bonds, continued Sharing electrons to form cmpds: COVALENT bonds are formed when electrons are SHARED between atoms in order to satisfy both. These bonds usually form between two nonmetal elements. These are stronger than ionic bonds.

Lesson 3.3: Chemical Formulas Formulas use elemental symbols and subscript numbers to how many atoms of which elements are in the compounds. Also shows the set ratio of the elements in a compound. Groups of more than one atom that move together are called radicals (pg 80) or polyatomic ions.

List rules for Naming Compounds & Writing Chemical Formulas. The positive ion goes first in any cmpd formula. Na & Cl = Na+ and Cl- so its NaCl (ionic) H & O = H+ and O- so its H2O (covalent) b) Use the regular first element name and add –ide to the second, or negative, element. If the second element is a polyatomic ion, add –ate or –ide. KCl = potassium chloride Cu(SO4) = copper sulfate Play the bonding game.

Lesson 3.4: What is a Reaction? Chemical changes produce new substances. During a reaction, atoms are rearranged (electrons are shared or transferred) in new ways. Making physical mixtures is simply putting substances together, but they DO NOT make new substances.

Making Mixtures Dissolving = putting a substance (solute) in a liquid (solvent) causes the atoms or ions to separate. Solvent = substance capable of dissolving other substances; water is the universal solvent. Solute = substance that dissolves in another substance.

Lesson 3.5: Using Equations to Show Reactions Conservation of mass states that mass can neither be created or destroyed. In a chemical reaction, atoms can neither be created or destroyed, only rearranged. Therefore, the atoms on the reactants side must equal the atoms on the products side of the arrow.

Balancing Chemical Equations In a balanced chemical equation, there are equal numbers of the atoms of each element on both sides of the arrow. Left side is the reactants & the right is the products. The arrow is read ‘goes to form’ or ‘yields.’ Numbers in front of a formula are coefficients & indicate the amt of that cmpd needed.

Rules for Balancing Equations: 1.) Write a word equation , then a chemical equation. Make sure symbols & formulas are correct. 2.) Count the number of atoms on both sides to see if they are equal. 3.) Put coefficients in front of symbols or formulas to balance the number of atoms. 4.) Recheck to see if it is balanced.

Checking an Equation Practice C + O2 > CO2 H2 + O2 > H2O Check if the following equations are balanced. We will balance if they aren’t. C + O2 > CO2 H2 + O2 > H2O On your own: Nitrogen and hydrogen are combined in a reaction to produce ammonia (NH3).

Balancing Equation Practice Balancing equations practice. 1-good lesson & practice;  2.-demo & game;   3.-practice quiz; 4.-more practice; and 5. more 

Types of equations Chemical rxns always have a change in energy. a. Endothermic rxns – energy is absorbed by reactants b. Exothermic rxns – energy is released as chem bonds reform Chemical reactions are grouped in 4 categories: Synthesis Reactions Decomposition Reactions Single-Replacement Reactions Double-replacement Reactions

Types of equations