Chapter 6.2 part 1

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Chapter 6.2 part 1

• Covalent bonding

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Covalent Bonding

• A metal and a nonmetal transfer electrons
• An ionic bond
• Two metals just mix and dont react
• An alloy
• What do two nonmetals do?
• Neither one will give away an electron
• So they share their valence electrons
• This is a covalent bond

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Covalent bonding

• Makes molecules
• Specific atoms joined by sharing electrons
• Two kinds of molecules
• Molecular compound
• Sharing by different elements (ex H2O
• Diatomic molecules
• Two of the same atom

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Diatomic elements

• There are 8 elements that always form molecules
• H2 , N2 , O2 , F2 , Cl2 , Br2 , I2 , and At2
• Oxygen by itself means O2
• The gens and the ines
• 1 7 pattern on the periodic table

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1 and 7
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Molecular compounds

• Tend to have low melting and boiling points
• Have a molecular formula which shows type and
  number of atoms in a molecule
• Not necessarily the lowest ratio
• C6H12O6
• Formula doesnt tell you about how atoms are
  arranged

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How does H2 form?

• The nuclei repel

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How does H2 form?

• The nuclei repel
• But they are attracted to electrons
• They share the electrons
• The average distance between nucleii is the bond
  length

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Bond Dissociation Energy (bond energy)

• The energy required to break a bond
• C - H 393 kJ/mol C H
• Short bonds are stronger than long bonds
• Double bonds have larger bond dissociation
  energies than single
• Triple even larger
• C-C 347 kJ
• CC 657 kJ
• CC 908 kJ

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Bond Dissociation Energy

• The larger the bond energy, the harder it is to
  break
• Large bond energies make chemicals less reactive.

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6.2 part 2

• Drawing covalent bond structures
• Electron dot diagrams
• Lewis structures

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Covalent bonds REVIEW

• Nonmetals hold onto their valence electrons.
• They cant give away electrons to bond.
• Still need noble gas configuration.
• Get it by sharing valence electrons with each
  other.
• By sharing both atoms get to count the electrons
  toward noble gas configuration.

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Single Covalent Bond

• A sharing of two valence electrons.
• Only nonmetals and Hydrogen.
• Different from an ionic bond because they
  actually form molecules.
• Two specific atoms are joined.
• In an ionic solid you cant tell which atom the
  electrons moved from or to.

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Covalent bonding Electron dot diagrams diatomic
molecule

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons
• Both end with full orbitals

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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons
• Both end with full orbitals

F
F
8 Valence electrons
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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons
• Both end with full orbitals

F
F
8 Valence electrons
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Rules for Lewis Structures

• Mr Sewalls rules.

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Lewis structures

• Are models showing the arrangement of atoms and
  bonds for molecules with known formulas

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Basic Lewis Structure

• Follows the octet rule
• Works on main block elements
• No one element can have more than 8 electrons
• Some my have less ex., H, He, Li, Be, and B
• a valence electron
• valence electrons main block family s-p
  number.
• bonds are joined s (electrons)

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Allowed Lewis structures

• All elements must be bonded
• No unpaired electrons
• No atom has more than 8 electrons

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Practice with a 2 atom molecule

• Start with the formula Cl2
• Write the symbols
• Cl Cl
• Give each its valence electrons

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Practice with a 2 atom molecule

• Connect the unpaired electrons to form bonds
• Count electrons bonded count as two for each
  atom

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LEWIS STRUCTURES WITH MORE THAN 2 ATOMS

• FIND THE CENTRAL ATOM
• ARRANGE ATOMS
• DRAW VALENCE ELECTRONS ON ATOMS
• CONNECT ATOMS WITH UNPAIRED ELECTRONS
• CHECK THAT OCTET RULE IS FOLLOWED ALL ELECTRONS
  ARE PAIRED

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Determine the central atom

• The central atom will be
• Carbon or
• The atom with the lowest electronegativity and a
  single atom
• If Carbon is present it will always form a
  backbone structure
• It can never be any element from the first family
  s1
• Why?

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Arranging Atoms Around Central Atom or Carbon
Backbone

• Hs are on the outside and evenly distributed
• Special organic functional groups such as
• -OH, -COOH, -NH2, are indicated in the formula

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PRACTICE WITH LEWIS STRUCTURES WITH MORE THAN 2
ATOMS

• Single bond
• CH3I,
• CH3CH2OH
• multiple bonds
• HCN,
• O2,
• CO2

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LEWIS STRUCTURES WITH MORE THAN 2 ATOMS

• Coordinate covalent bonds and resonance
  structures (O3)

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Coordinate covalent bonds and resonance
structures (O3)

• if connecting single electrons does meet octet
  rule
• Then use paired electrons from one to make bond
  coordinate covalent bond

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Coordinate Covalent Bonds And Resonance Structures

• Single bonds give 8 electrons to central atom but
  only 7 to each outside atom

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Resonance structure and coordinate covalent bonds

• Instead complete the bond to two atoms
• The third atom bond comes from the shared
  electrons of the central atom

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Resonance structure and coordinate covalent bonds

• Pair up the single electrons
• Use a pair of electrons from the central atom as
  the bonding pair
• Check the rules.

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RESONANCE STRUCTURES (O3)

• NOTE THAT THE BOND CAN BE DRAWN TO EITHER OXYGEN
• MEASUREMENTS SHOW THAT THE BONDS ARE ALL THE SAME
  LENGTH
• SO THE DOUBLE BOND RESONATES ACROSS THE MOLECULE
• IT IS NOT A DOUBLE AND SINGLE BOND BUT TWO 1.5
  BONDS

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PRACTICE SOME CCBS AND RESONANCE STRUCTURES

• SO2
• SO3,

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Lewis structures for molecular ions.

• Same rules as for molecular compounds and you are
  adding (anions) or removing (cations)
• After placing electrons on atoms, add or remove
  electrons from the central atom to adjust the
  charge on the ion.
• Finish drawing the Lewis structure following the
  rules for molecular compounds

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Practice for Lewis structures for molecular ions.

• NO3-
• HCO3-
• SO42-
• NH4

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How to show how they formed

• Its like a jigsaw puzzle.
• I have to tell you what the final formula is.
• You put the pieces together to end up with the
  right formula.
• For example- show how water is formed with
  covalent bonds.

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Water

• Each hydrogen has 1 valence electron
• and wants 1 more
• The oxygen has 6 valence electrons
• and wants 2 more
• They share to make each other happy

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Water

• Put the pieces together
• The first hydrogen is happy
• The oxygen still wants one more

H
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Water

• The second hydrogen attaches
• Every atom has full energy levels

H
H
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Multiple Bonds

• Sometimes atoms share more than one pair of
  valence electrons.
• A double bond is when atoms share two pair (4) of
  electrons.
• A triple bond is when atoms share three pair (6)
  of electrons.

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Carbon dioxide

• CO2 - Carbon is central atom ( I have to tell
  you)
• Carbon has 4 valence electrons
• Wants 4 more
• Oxygen has 6 valence electrons
• Wants 2 more

C
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Carbon dioxide

• Attaching 1 oxygen leaves the oxygen 1 short and
  the carbon 3 short

C
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Carbon dioxide

• Attaching the second oxygen leaves both oxygen 1
  short and the carbon 2 short

C
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Carbon dioxide

• The only solution is to share more

C
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Carbon dioxide

• The only solution is to share more

C
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Carbon dioxide

• The only solution is to share more

C
O
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Carbon dioxide

• The only solution is to share more

C
O
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Carbon dioxide

• The only solution is to share more

C
O
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Carbon dioxide

• The only solution is to share more

C
O
O
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Carbon dioxide

• The only solution is to share more
• Requires two double bonds
• Each atom gets to count all the atoms in the bond

C
O
O
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Carbon dioxide

• The only solution is to share more
• Requires two double bonds
• Each atom gets to count all the atoms in the bond

8 valence electrons
C
O
O
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Carbon dioxide

• The only solution is to share more
• Requires two double bonds
• Each atom gets to count all the atoms in the bond

8 valence electrons
C
O
O
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Carbon dioxide

• The only solution is to share more
• Requires two double bonds
• Each atom gets to count all the atoms in the bond

8 valence electrons
C
O
O
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Polar Bonds

• When the atoms in a bond are the same, the
  electrons are shared equally.
• This is a nonpolar covalent bond.
• When two different atoms are connected, the
  electrons may not be shared equally.
• This is a polar covalent bond.
• How do we measure how strong the atoms pull on
  electrons?

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Electronegativity

• A measure of how strongly the atoms attract
  electrons in a bond.
• The bigger the electronegativity difference the
  more polar the bond.
• Use table 12-3 Pg. 285
• 0.0 - 0.4 Covalent nonpolar
• 0.5 - 1.0 Covalent moderately polar
• 1.0 -2.0 Covalent polar
• gt2.0 Ionic

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How to show a bond is polar

• Isnt a whole charge just a partial charge
• d means a partially positive
• d- means a partially negative
  
• The Cl pulls harder on the electrons
• The electrons spend more time near the Cl

d
d-
H
Cl
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Polar Molecules

• Molecules with ends

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Polar Molecules

• Molecules with a partially positive end and a
  partially negative end
• Requires two things to be true
• The molecule must contain polar bonds
• This can be determined from differences in
  electronegativity.
• Symmetry can not cancel out the effects of the
  polar bonds.
• Must determine geometry first.

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Polar Molecules

• Symmetrical shapes are those without lone pair on
  central atom
• Tetrahedral
• Trigonal planar
• Linear
• Will be nonpolar if all the atoms are the same
• Shapes with lone pair on central atom are not
  symmetrical
• Can be polar even with the same atom

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Is it polar?

• HF
• H2O
• NH3
• CCl4
• CO2
• CH3Cl

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Hydrogen bonding
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Properties of Molecular Compounds

• Made of nonmetals
• Poor or nonconducting as solid, liquid or aqueous
  solution
• Low melting point
• Two kinds of crystals
• Molecular solids held together by IMF
• Network solids- held together by bonds
• One big molecule (diamond, graphite)