What is a chemical change? – New substance formed; different properties from the reactants How do we know a chemical reaction has taken place? – (1). Formation of a gas – (2). Permanent color change – (3). Temperature change Exothermic and endothermic – (4). Precipitant formed What is a chemical change? – New substance formed; different properties from the reactants How do we know a chemical reaction has taken place? – (1). Formation of a gas – (2). Permanent color change – (3). Temperature change Exothermic and endothermic – (4). Precipitant formed

How do elements form compounds? – Atoms of the reactant(s) are rearranged and bond in different combinations – A + B  C + D – Phase Changes and Chemical changes Animation Phase Changes and Chemical changes Animation How do elements form compounds? – Atoms of the reactant(s) are rearranged and bond in different combinations – A + B  C + D – Phase Changes and Chemical changes Animation Phase Changes and Chemical changes Animation

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Note that elements within the same group have the same electron-dot structure.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Valence electrons: Electrons in the outermost shell of an atom. These are the ones that can participate in chemical bonding. Electron-dot structure: A notation showing the valence electrons surrounding the atomic symbol.

(1). Ionic – Metals transfer electrons to nonmetals – Positive ions (cations) and Negative ions (anions) are formed (2). Covalent – Sharing of electrons between nonmetal atoms – Equal sharing: nonpolar compound – Unequal sharing: polar compound (3). Metallic – Sea of electrons float between metal atoms (1). Ionic – Metals transfer electrons to nonmetals – Positive ions (cations) and Negative ions (anions) are formed (2). Covalent – Sharing of electrons between nonmetal atoms – Equal sharing: nonpolar compound – Unequal sharing: polar compound (3). Metallic – Sea of electrons float between metal atoms

Characteristics – (1). Electrostatic Attraction between positive and negative ions – (2). Formation of Crystal Structures – (3). Strong Bonds – High Melting Points – (4). Electrolytes – Animation Animation Characteristics – (1). Electrostatic Attraction between positive and negative ions – (2). Formation of Crystal Structures – (3). Strong Bonds – High Melting Points – (4). Electrolytes – Animation Animation

Electronegativity: The ability of a bonded atom to pull on shared electrons. Greater electronegativity means greater “pulling power.” Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley High Low

Characteristics (1). Sharing of electrons between atoms (2). Electronegativity is similar (3). Molecules formed (4). Bonds not as strong as covalent (5). May be equal or unequal sharing between electrons (6). Gases form covalent bonds Characteristics (1). Sharing of electrons between atoms (2). Electronegativity is similar (3). Molecules formed (4). Bonds not as strong as covalent (5). May be equal or unequal sharing between electrons (6). Gases form covalent bonds

The type of electrical attraction in which atoms are held together by their mutual attraction for shared electrons. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley

The type of electrical attraction in which atoms are held together by their mutual attraction for shared electrons. There are two electrons within a single covalent bond. The covalent bond is represented using a straight line. The type of electrical attraction in which atoms are held together by their mutual attraction for shared electrons. There are two electrons within a single covalent bond. The covalent bond is represented using a straight line. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley F — FF

Electrons within a covalent bond are shared evenly when the two atoms are the same. They may be shared unevenly, however, when the bonded atoms are different. Electrons within a covalent bond are shared evenly when the two atoms are the same. They may be shared unevenly, however, when the bonded atoms are different. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley

But if polar bonds within a molecule are facing in equal and opposite directions… …then the polarity may cancel itself out. But if polar bonds within a molecule are facing in equal and opposite directions… …then the polarity may cancel itself out. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley

But if polar bonds within a molecule are facing in equal and opposite directions… …then the polarity may cancel itself out. But if polar bonds within a molecule are facing in equal and opposite directions… …then the polarity may cancel itself out. Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley …or not!

Animation – Chemistry Comes Alive Dust Explosion Animation Animation – Chemistry Comes Alive Dust Explosion Animation

Characteristics Electrons of metal atoms flow freely between other metal atoms The more mobile the electrons, the better the electrical conductor Higher the vibration of electrons more metal is shiny. Malleable characteristic due to electrons not being fixed, but freely flowing Alloy: White gold (molten gold and palladium are blended) Characteristics Electrons of metal atoms flow freely between other metal atoms The more mobile the electrons, the better the electrical conductor Higher the vibration of electrons more metal is shiny. Malleable characteristic due to electrons not being fixed, but freely flowing Alloy: White gold (molten gold and palladium are blended)

High luster, shiny Malleable Ductile High Melting Points Good Conductors Poor Insulators High luster, shiny Malleable Ductile High Melting Points Good Conductors Poor Insulators Low luster and dull Nonmalleable Not Ductile Low Melting Points Poor Conductors Good Insulators Low luster and dull Nonmalleable Not Ductile Low Melting Points Poor Conductors Good Insulators