Transcript Chemical Bonds and Chemical Changes PP

ISCI 2002
Matter and Chemical Reactions
• 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
Matter and Chemical Reactions
• 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
Electron Shells
Note that elements within the same group
have the same electron-dot structure.
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Education, Inc., publishing as
Pearson Addison Wesley
Electron Shells
• 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.
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Education, Inc., publishing as
Pearson Addison Wesley
Chemical Bonds
• (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
Ionic Bonding
• Characteristics
– (1). Electrostatic Attraction between
positive and negative ions
– (2). Formation of Crystal Structures
– (3). Strong Bonds – High Melting Points
– (4). Electrolytes
– Animation
Polar Bonds and Polar Molecules
• Electronegativity: The ability of a bonded
atom to pull on shared electrons.
Greater electronegativity means greater
“pulling power.”
High
Low
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Covalent Bonding
• 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 Covalent Bond
• The type of electrical attraction in which
atoms are held together by their mutual
attraction for shared electrons.
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Education, Inc., publishing as
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The Covalent Bond
• 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.
F F
F—F
Copyright © 2007 Pearson
Education, Inc., publishing as
Pearson Addison Wesley
Polar Bonds and Polar Molecules
• 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
Polar Bonds and Polar Molecules
• 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
Polar Bonds and Polar Molecules
• But if polar bonds within a molecule are
facing in equal and opposite directions…
…then the polarity may cancel itself out.
…or not!
Copyright © 2007 Pearson
Education, Inc., publishing as
Pearson Addison Wesley
More Chemical Reactions
• Animation – Chemistry Comes Alive
• Dust Explosion Animation
Metallic Bonding
• 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)
Metals vs Nonmetals
•
•
•
•
•
•
Metals
High luster, shiny
Malleable
Ductile
High Melting Points
Good Conductors
Poor Insulators
•
•
•
•
•
•
Non-Metals
Low luster and dull
Nonmalleable
Not Ductile
Low Melting Points
Poor Conductors
Good Insulators
Atomic Size/Radius
• Half the distance between the centers of
two atoms of that element that are
touching each other.
: Decreases left to right
– Why?
: increases as you go down
– Why?
Ionization Energy
• Energy required to completely remove
an electron from a gaseous atom or ion.
: Increases from left to
right
– Right side: increasing nuclear charge
holds atoms tighter
: Decreases as you go
down the group
– Atomic radius increases; electrons father
away from the nucleus