CHEMICAL BONDS

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CHEMICAL BONDS

• A Dogs Tale about an
• Elements Search for Happiness
• (chemical stability)

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CHEMICAL BONDS

• The forces that hold atoms togetheroften driven
  by the Octet Rule and stability.
• (Mutual electrical attraction between nuclei and
  valence electrons of different atoms that binds
  them.)

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Chemical Bonds

• Sometimes it helps to think of bonds (which you
  can't see) in terms of familiar things you can
  see.  This is called an analogy. 
• Let's use the natural attraction of dogs to bones
  as an analogy to the attractions that cause
  chemical bonds.

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Chemical Bonds

• The negatively charged electrons determine how
  two or more atoms will interact when they are
  brought near each other.  In a sense, the atoms
  fight over the available electrons in much the
  same way two or more dogs will fight over bones. 
  
• The Dog Bone Analogy works quite well for
  several types of atomic bonds. 
• Dogs are the atoms.
• Bones are the electrons.

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Octet Rule Atoms tend to gain, lose, or share
electrons in order to acquire a full set of
valence electrons.
8 (most of the time)
2 (1st energy level)
or
Happy dogs!
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IONIC BONDS

• One big greedy thief dog!Ionic bonding can be
  best imagined as one big greedy dog stealing the
  other dog's bone. 

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IONIC BONDS

• The bone represents the electron that is up for
  grabs.
• When the big dog gains an electron he becomes
  negatively charged, and the little dog who lost
  the electron becomes positively charged. 
• These two ions (that's where the name ionic
  comes from) are attracted very strongly to each
  other as a result of the opposite charges.

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IONIC BONDSChemical bonding that results from
transfer of electrons and electrical attraction
between cations and anions.

• Form between metals (on the left side of the
  Periodic Table) and non-metals (on the right side
  of Periodic Table)
• Metal loses electron(s) and becomes positively
  chargeda cation.
• Non-metal gains electron(s) and becomes
  negatively chargedan anion.
• The oppositely charged ions are held together
  because they are strongly attracted to each
  other.
• Determine difference in electronegativity
• See page 161
• Difference of greater than 1.7 is often
  considered ionic
• Ionic character greater than 50

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IONIC BOND?

• Cs and F?
• Page 161 electronegativity chart
• F en 4.0
• Cs en 0.7
• --------------
• 3.3 is the electronegativity
  difference
• A bond between Cs and F is ionic, greater than
  1.7

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IONIC COMPOUNDS

• Expressed as formula units rather than
  molecules because they form networks of ions
  attracted to each othernot independent neutral
  units.
• Characteristics
• Crystalline structure
• High melting points
• Brittle
• Dissolve in water
• This separates the ions by breaking the ionic
  bondsseparated ions move freely making solution
  of ionic compounds good conductors of
  electricity.
• Also conductive when melted.

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Formula unit is NaCl, 1 sodium and 1 choride, the
simplest ratio

• Ionic compounds form orderly arrangements of the
  ions , called crystal lattices.

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(No Transcript)
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COVALENT BONDS The dogs share the bones.
There are two types of sharing
UNEQUAL
EQUAL
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COVALENT BONDSBonds formed when electrons are
shared

• Covalent bonds form between non-metals(on the
  right side of the Periodic Table)
• The electrons are shared by the atoms.
• Electrons may be shared equally or unequally.
• Molecules are formed because atoms sharing
  electrons must be near each other

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COVALENT BONDS

• Enormous variety of size, shape, physical, and
  chemical properties.
• often lower melting point,
• not necessarily crystalline
• do not conduct electricity,
• may or may not dissolve in water

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POLAR COVALENT BONDS

• Unevenly matched dogs that are willing to
  share.These bonds can be thought of as two or
  more dogs that have different desire for
  bones. They share unequally.

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POLAR COVALENT BONDS

• The bigger dog has more strength to possess a
  larger portion of the bones.  Sharing still takes
  place but is an uneven sharing. 

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POLAR COVALENT BONDS

• In a covalent bond, the electrons are shared
  between atoms to fulfill the Octet Rule for both.
• In a polar covalent bond, the electrons are
  shared unequally. They are attracted more to the
  more electronegative element.
• The electrons spend more time near the more
  electronegative element, making it seem more
  negative and the other end of the molecule seem
  more positiveor polar
• Determine difference in electronegativity
• See page 161
• Difference of .3-1.7 is often considered polar
  covalent
• Ionic character 5-50

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POLAR COVALENT BOND?

• Unequal sharing of electrons

Partial negative charge
Partial positive charge
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POLAR COVALENT BOND?

• H and S?
• Page 161
• S en 2.5
• H en 2.1
• --------------
• 0.4 is the electronegativity
  difference
• A bond between H and S is polar covalent, .3-1.7

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Polar molecules and polar bonds
Two sides to the molecules/bonds
Partial positive charge towards less
electronegative element
Partial negative charge towards element with
greater electronegativity.
S
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Polar bonds lead to polar molecules
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Polamolecules
Two sides to Troy Polamalu
Calm, quiet, humble on the sideline
Fearless, crazed, maniacal on the field
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Polar molecules and polar bonds
Two sides to the molecules/bonds
Partial positive charge towards less
electronegative element
Partial negative charge towards element with
greater electronegativity.
S
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NON-POLAR COVALENT BONDS

• Covalent Bonds Dogs of equal strength share
  equally.Covalent bonds can be thought of as two
  or more dogs with equal attraction to the bones. 
• They share equally.

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NON-POLAR COVALENT BONDS

• Since the dogs are identical, then the dogs
  share the bones evenly.  Since one dog does not
  have more of the bone than the other dog, the
  bone is equally shared between both dogs. One dog
  does not have more than the other.

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NON-POLAR COVALENT BONDS

• In a covalent bond, the electrons are shared
  between atoms to fulfill the Octet Rule for both.
• In a non-polar covalent bond, the electrons are
  shared equally.
• The charge is evenly distributed between both
  atoms.  The molecule is non-polar meaning one
  side does not have more charge than the other.
• Determine difference in electronegativity
• See page 161
• Difference of less than .3 is often considered
  nonpolar covalent
• Ionic character less than 5

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NON-POLAR COVALENT BOND?

• Cl and Br?
• Page 161 for en
• Cl en 3.0
• Br en 2.8
• --------------
• 0.2 is the electronegativity
  difference
• A bond between Cl and Br is nonpolar covalent,
  less than 0.3

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NON-POLAR COVALENT BOND?

• Equal sharing of electrons

Equal distribution of charge
Equal distribution of charge
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Diatomic ElementsThey pair up!

• Br2
• I2
• N2
• Cl2
• H2
• O2
• F2

The diabolical DIATOMIC BrINClHOF TWINS!
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METALLIC BONDS

• Mellow dogs with plenty of bones to go around.
  They dont have to worry about sharing!

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METALLIC BONDS

• These bonds are best imagined as a room full of
  puppies who have plenty of bones to go around and
  are not possessive of any one particular bone. 
  This allows the electrons to move through the
  substance with little restriction.  The model is
  often described as the "kernels of atoms in a sea
  of electrons.

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METALLIC BONDs

• Electrons are delocalized
• Electrons move freely around and between atoms in
  the network of empty orbitals. The electrons move
  through the substance with little restriction. 
  The model is often described as the "kernels of
  atoms in a sea of electrons.

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METALLIC BONDS

• The free movement of electrons explains the
  properties of metals
• Conductivity free movement of electrons
• Malleability ductility bonding is the same in
  all directions
• Luster energy released as electrons move easily
  between orbitals

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We will look more closely at the different types
of bonds to understand how millions of different
compounds form from only about 100 different
elements!
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Lewis Dot of Ionic Compounds (electrons taken,
not shared)

• Write the dot structures of the neutral atoms
• Write the ions created by the loss or gain of
  electrons, in brackets. The metals have no dots.
  The non-metals have a full outer shell.
• Show the ion charges as superscripts.
• Show the ratio of ions needed to create a net
  charge of zero.

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Criss-Cross Method to Determine Ratio of Ions

• Write the ion symbols and charges (superscripts).
  Get this info from periodic table for elements,
  polyatomic ion list for polyatomic ions.
• Criss-cross the charge (numbers only) to
  subscripts. This shows the ratio of ions required
  for a net charge of zero.
• Simplify. Mg2 N3-
• Mg3N2

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Charges of ions from PT
group 1 2 13 14 15 16 17 18
ve 1 2 3 4 5 6 7 2 or 8
charge 1 2 3 4/- 3- 2- 1- 0
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Why does it work?

• The goal is a net charge of 0. The charges, or
  oxidation numbers, must add up to zero.
• Mg3N2
• 3 x 2 6
• 2 x 3- 6-
• 0 net charge

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Lewis Dot Structures of Covalent Bonds(shared
electrons)

• Lewis dot structures show atoms near each other
  sharing pairs of electrons to create bonds and
  satisfy octet rule for both atoms.
• They may share up to 3 pairs of electrons
• 1 SHARED PAIR SINGLE BOND
• 2 SHARED PAIRS DOUBLE BOND
• 3SHARED PAIRS TRIPLE BOND
• It does not matter which atom the electrons come
  from because they are shared.

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Covalent bonds usually follow the octet rule

• Put all of the valence electrons in a pot and
  distribute them between the atoms so each atom
  has a full octet by sharing up to 3 pairs of
  electrons.

single bond double bond triple bond