Chemical Bonding and Chemical Reactions Chapter 16 and 17 Chemical Bonding and Chemical Reactions

Chemical Bonding The force that holds two atoms together Unites atoms in a molecule Atoms bond so they will become more stable. Their outer rings will resemble the noble gases.

Ionic Bonds Ion Ionic Bond Atom that has lost or gained an electron Is now positive or negatively charged Ionic Bond Attraction that holds oppositely charged ions close together Positive Na ion and negative Cl ion are attracted to one another.

Ionic Bond

Covalent Bonds Chemical bond that forms between nonmetal when they share electrons Electrons move back and forth between the outer energy levels of each atom to maintain the covalent bond

Molecule The neutral particle formed when atoms combine 2 Types: Element or Compound Element—Molecule formed from 1 type of atom Compound—Molecule formed from 2 or more types of atoms

Symbols for Compounds Compounds can be described using element symbols and numbers Subscripts (small numbers) after the letters tell how many of that element are in a molecule. Example: H2O contains 2 Hydrogen atoms and 1 oxygen atom.

Chemical Formula Combination of chemical symbols and numbers that shows which elements are present in a compound and how many atoms of each element are present. Examples: Ammonia: NH3 Silver Tarnish: Ag2S Hydrogen Gas: H2

Chapter 17 Chemical Reactions

Physical or Chemical Change? Physical Change Affects the physical appearance of a substance Changes in state Changes in shape or size Chemical Change Produces a new substance during a chemical reaction Produces gas, light, change in heat, precipitate, change in color, sound Oxidation, Burning

Physical or Chemical Change?

Chemical Equations Describes the reactants and products in a chemical reaction using symbols and numbers Reactants Substances that exist before the reaction begins Products Substances that form as a result of the reaction

Writing Chemical Equations Reactants Products 2H2 + O2 2H20 Hydrogen + Oxygen Water 2 Ag + H2S Ag2S + H2 Silver + Hydrogen Sulfide Silver Sulfide + Hydrogen

Conservation of Mass Matter is not created or destroyed Every atom that appears on the reactant side of the reaction also appears on the product side of the reaction

Balancing Equations Ag + H2S Ag2S + H2 H2 + O2 H20

pH Scale Scale used to measure the strength of an acid or base. 1---6.5 is considered an acid (battery acid) Releases H+ ions in a solution 7 is considered neutral (water) 7.5—14 is considered a base (lye, soap) Releases OH– ions in a solution

pH Scale

Energy in Chemical Reactions Endothermic Reaction Reaction that absorbs heat energy (gets colder) 2H20 + energy 2H2 + O2 Exothermic Reaction Reaction that releases heat energy (gets warmer) CH4 + 2O2 CO2 + H2O + energy

Activation Energy Minimum amount of energy need to start a chemical reaction Example—burning of gasoline

Catalyst A substance that speeds up a chemical reaction Are not changed permanently or used up during a chemical reaction Enzymes Special Catalysts that speed up chemical reactions in cells.

Inhibitor Substance that slows down a chemical reaction Makes the formation of a certain amount of product take longer