COVALENT BONDING

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COVALENT BONDING

• Chapter 16

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AND THE SUBJECTS ARE

• THE NAME IS BOND, COVALENT BOND
• SINGLES, DOUBLES TRIPPPLES
• COORDINATE COVALENT BONDS
• RESONATE THIS!
• THERES ALWAYS AN EXCEPTION
• PRINCESS VSEPR
• HYBRIDS
• DISSOCIATIONS AND ATTRACTIONS

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YOU KNOW THAT YOU MAY BE A COVALENT BOND WHEN

• ELECTROSTATIC FORCES ARE WEAK
• r ELECTRONEGATIVITY IS SMALL
• THERE ARE NO METAL CATIONS
• IONS DONT GET OR LOSE ELECTRONS

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SINGLE COVALENT BOND

• HYDROGEN
• H H ? HH
• Hydrogen Hydrogen Hydrogen
• Atom Atom
  molecule
• HYDROGEN ATOMS FORM SINGLE BONDS

Shared electron pair
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SINGLE COVALENT BOND

• DIATOMIC MOLECULES
• HYDROGEN NITROGEN OXYGEN FLUORINE
  CHLORINE BROMINE
• IODINE
• r ELECTRONEGATIVITY 0
• SHARED ELECTRONS

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SINGLE COVALENT BOND

• FOR CHLORINE,
• 1s 2s 2p 3s 3p
• Cl ?? ?? ?? ?? ?? ?? ?? ?? ?_
• Cl ?? ?? ?? ?? ?? ?? ?? ?? _?

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SINGLE COVALENT BONDDEFINITIONS

• EMPIRICAL FORMULA - LOWEST WHOLE NUMBER RATIO OF
  ELEMENTS IN A COMPOUND
• MOLECULAR FORMULA SHOWS ACTUAL NUMBER AND KINDS
  OF ELEMENTS IN A COMPOUND
• STRUCTURAL FORMULA SHOWS ARRANGEMENT OF ATOMS
  IN A COMPOUND

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SINGLE COVALENT BOND
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SINGLE COVALENT BOND

• ELECTRON PAIRS REPRESENTED BY A LINE BETWEEN 2
  ELEMENTS
• H - H
• OTHER ELECTRONS MUST BE SHOWN, INCLUDING
• UNSHARED PAIRS
• LONE PAIRS
• NON-BONDING PAIRS

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2 CHLORINE ATOMS FORM A COVALENT BOND

• SINGLE COVALENT BOND

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WATER MOLECULE FORMED FROM 1 OXYGEN AND 2
HYDROGEN ATOMS USING COVALENT BONDS

• SINGLE COVALENT BOND

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SINGLE COVALENT BOND

• CARBON FORMS UP TO 4 BONDS
• C ?? ?? ?_ ?_
• 1s 2s 2p
• TO MAKE THE 4TH BOND, A 2s ELECTRON MOVES TO A
  2p ORBITAL
• C ?? ?_ ?_ ?_ ?_
• 1s 2s 2p

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• DOUBLE AND TRIPLE COVALENT BONDS

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CORDINATE COVALENT BONDS

• BOND FORMED WHEN BOTH ELECTRONS DONATED BY THE
  SAME ATOM

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POLYATOMIC IONS

• POLYATOMIC IONS ARE COVALENTLY BONDED
• THE CHARGE ON THE ION SHOWS THE NUMBER OF
  ELECTRONS ADDED OR MISSING

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RESONANCE

• RESONANCE STRUCTURES SHOW 2 OR MORE VALID DOT
  FORMULAS HAVING THE SAME NUMBER OF BONDS AND
  ELECTRONS

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EXCEPTIONS to the OCTET RULE

• IN SOME MOLECULES, THE OCTET RULE CANNOT BE
  SATISFIED

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EXCEPTIONS to the OCTET RULE

• DIAMAGNETIC ALL ELECTRONS PAIRED
• PARAMAGNETIC - 1 OR MORE UNPAIRED ELECTRONS
• EXPANDED OCTET MAY INCLUDE MORE THAN 8
  ELECTRONS

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MOLECULAR ORBITALS (MO)

• WHEN 2 ATOMIC ORBITALS OVERLAP,
• 2 MOLECULAR ORBITALS FORM
• 1 ORBITAL IS BONDING
• ENERGY LOWER THAN ATOMIC ORBITAL
• 1 ORBITAL IS ANTI-BONDING
• ENERGY HIGHER THAN ATOMIC ORBITAL
• ORBITAL BELONGS TO MOLECULE AS A WHOLE
• ORBITAL CONTAINS UP TO 2 ELECTRONS

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MOLECULAR ORBITALS
Anti-bonding Molecular Orbital
Atomic Orbital
Atomic Orbital
Energy
Bonding Molecular Orbital
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MOLECULAR ORBITALSHYDROGEN

• TWO H2 MOLECULE ELECTRONS OCCUPY A BONDING
  ORBITAL
• PROBABILITY OF FINDING ELECTRONS IN THE AREA
  BETWEEN 2 ATOMS IS HIGH
• BOND IS SYMETRICAL ALONG AXIS BETWEEN ATOMS
• CALLED A SIGMA (s) BOND

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MOLECULAR ORBITALS
H2
Anti-bonding Molecular Orbital
Atomic Orbital
Atomic Orbital
?
?
Energy
??
Bonding Molecular Orbital
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MOLECULAR ORBITALS (MO)
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MOLECULAR ORBITALSHELIUM

• 2 MOLECULES OF He CANNOT BE FORMED
• 2 ELECTRONS IN BONDING ORBITAL
• 2 ELECTRONS IN ANTI-BONDING ORBITAL
• REPULSIVE FORCES IN ANTI-BONDING ORBITAL NEGATES
  ATTRACTIVE FORCES IN BONDING ORBITAL

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MOLECULAR ORBITALS
He
Anti-bonding Molecular Orbital
??
Atomic Orbital
Atomic Orbital
??
??
Energy
??
Bonding Molecular Orbital
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MOLECULAR ORBITALS

• p ORBITALS CAN OVERLAP
• OVERLAP END-TO-END SIGMA (s) BOND
• OVERLAP SIDE-BY-SIDE PI (P) BOND

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MOLECULAR ORBITALS
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MOLECULAR ORBITALS
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VALENCE SHELL ELECTRON PAIR REPULSION THEORYVSEPR

• ELECTRON PAIRS REPEL DUE TO THE SAME CHARGE
• MOLECULAR SHAPE ADJUSTS TO SET FURTHEST DISTANCE
  BETWEEN PAIRS
• CREATES 3 DIMENSIONAL STRUCTURES

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MOLECULES in 3-D

• METHANE (CH4)
• CARBON in CENTER, with H in the CORNERS to form a
  TETRAHEDRON
• H-C-H ANGLES ARE 109.5

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MOLECULES in 3-D
MOLECULAR GEOMETRY
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MOLECULES in 3-D

• UNSHARED ELECTRON PAIRS IMPACT SHAPE
• UNSHARED ELECTRONS HELD CLOSER TO NUCLEUS
• UNSHARED ELECTRONS ALSO MORE STRONGLY REPEL OTHER
  ATOMS

• ANGLE SHIFTS TO 107

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MOLECULES in 3-D

• DIHYDROGEN OXIDE (H2O)
• MOLECULE BECOMES BENT PLANAR WITH 2 PAIRS
  UNSHARED ELECTRONS
• UNSHARED PAIRS REPEL BONDING PAIRS, COMPRESSING
  ANGLE

• H-O-H ANGLE IS 105

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MOLECULES in 3-D

• CARBON DIOXIDE (CO2)
• NO UNSHARED ELECTRON PAIRS IN CARBON DIOXIDE
• MOLECULE IS LINEAR

ANGLE IS 180o
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MOLECULES in 3-D

• MOLECULES WITH NO UNPAIRED ELECTRONS, BUT WITH
  DOUBLE BOND
• MOLECULE IS TRIAGONAL PLANAR SHAPE

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HYBRID ORBITALS

• SEVERAL ATOMIC ORBITALS CAN MIX TO FORM HYBRID
  ORBITALS
• EACH ATOM HAS SEPARATE s AND p ORBITALS

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HYBRID ORBITALS

• SOME ATOMIC ORBITALS MERGE, FORMING 4 sp3 HYBRID
  ORBITALS
• EACH ORBITAL BENDS TOWARD CORNER OF TETRAHEDRON

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HYBRID ORBITALS

• METHANE (CH4)
• s ORBITALS OF HYDROGEN OVERLAP CARBON sp3
  ORBITAL
• FORMS s BONDS

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HYBRID ORBITALS

• DOUBLE BONDS
• ATOMIC ORBITALS IN DOUBLE BONDS MERGE TO FORM 3
  sp2 HYBRID ORBITALS 1 p ORBITAL REMAINS
• ORBITALS BEND TOWARD CORNER OF TRIANGLE,
  PERPENDICULAR TO REMAINING p ORBITAL

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HYBRID ORBITALS

• ETHYLENE (C2H4)
• HYDROGEN ORBITALS OVERLAP WITH CARBON sp2
  ORBITALS
• 1 sp2 ORBITAL FROM EACH CARBON BONDS
• REMAINING CARBON p ORBITALS FORM A P BOND

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HYBRID ORBITALS

• TRIPLE BONDS
• ATOMIC ORBITALS MERGE TO FORM 2 sp HYBRID
  ORBITALS, AND 2 p ORBITALS REMAIN
• ORBITAL IS LINEAR AND PERPENDICULAR TO REMAINING
  p ORBITALS

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HYBRID ORBITALS

• ACETYLENE (C2H2)
• HYDROGEN s ORBITALS OVERLAP WITH CARBON sp2
  ORBITALS, AND 1CARBON sp2 ORBITAL EACH BOND
• REMAINING CARBON p ORBITALS FORM P BOND

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POLAR BONDS

• BOND POLARITY
• ELECTRONS SHARED IN COVALENT BOND
• BUT NOT NECESSARILY EQUALLY
• NON-POLAR BONDS
• ELECTRONS SHARED EQUALLY
• POLAR BOND
• ELECTRONS PULLED STRONGLY TO ATOM WITH HIGHER
  ELECTRONEGATIVITY

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POLAR BONDS

• HYDROGEN IODIDE (HI)
• IODINE (EN 2.5) HAS A HIGHER ELECTRONEGATIVITY
  THAN HYDROGEN (EN 2.1)
• ELECTRONS DRAWN TOWARD IODINE NUCLEUS
• REPRESENTED BY
• d d-
• H I or H - I
• HYDROGEN DEVELOPS PARTIAL POSITIVE CHARGE, WHILE
  IODINE COUNTERS WITH A PARTIAL NEGATIVE CHARGE

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POLAR BONDS

• WATER AND CHLOROMETHANE ARE EXAMPLES OF POLAR
  MOLECULES

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POLAR BONDS

• TYPE OF BOND IS DETERMINED BY THE
  ELECTRONEGATIVITY OF THE BONDING ELEMENTS

Electronegativity Differences and Bond Type Electronegativity Differences and Bond Type Electronegativity Differences and Bond Type
Electronegativity Difference Type of Bond Example
0.0-0.4 Non-polar covalent H-H (0.0)
0.4-1.0 Moderately polar covalent H-Cl (0.9)
1.0-2.0 Very polar covalent H-F (1.9)
gt 2.0 Ionic NaCl- (2.1)
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POLAR MOLECULES

• POLAR MOLECULE HAS 1 OR MORE POLAR BONDS
• CHARGED REGION IS A POLE
• MOLECULE HAVING 2 POLES IS A DIPOLE
• WHEN POLAR MOLECULES ARE PLACED IN AN ELECTRIC
  FIELD, THEY BECOME ORIENTED WITH RESPECT TO THE
  FIELD

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POLAR MOLECULESIN AN ELECTRIC FIELD
Negative Plate
Positive Plate
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POLAR MOLECULES

• EFFECT OF POLAR BONDS ON THE MOLECULES POLARITY
  DEPENDS ON SHAPE OF THE MOLECULE AND POLAR BOND
  ORIENTATION
• WATER IS A POLAR MOLECULE, BUT CARBON DIOXIDE IS
  NOT

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BOND DISSOCIATION ENERGY

• ENERGY NEEDED TO BREAK A COVALENT BOND

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INTERMOLECULAR ATTRACTIONS

• INTERMOLECULAR FORCES
• DETERMINE COMPOUNDS PHYSICAL STATE
• VERY WEAK COMPOUND IS A GAS
• SOMEWHAT STRONGER COMPOUND IS A LIQUID
• MUCH STRONGER COMPOUND IS A SOLID
• MOLECULAR COMPOUND MELTING AND BOILING POINTS ARE
  LOWER THAN IONIC COMPOUNDS
• MOLECULAR COMPOUNDS ARE INSOLUBLE IN WATER
• MOLECULAR COMPOUNDS DO NOT CONDUCT ELECTRICITY IN
  THEIR LIQUID STATE

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Van der Waals FORCES

• DISPERSION FORCES
• CAUSED BY ELECTRON MOTION
• INCREASES AS ELECTRON NUMBER INCREASES
• DIPOLE INTERACTIONS
• ELECTROSTATIC INTERACTION BETWEEN OPPOSITE
  CHARGED REGIONS OF POLAR MOLECULES

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HYDROGEN BONDING

• CONDITIONS FOR HYDROGEN BONDING
• COVALENT HYDROGEN BOND WITH HIGHLY
  ELECTRONEGATIVE ELEMENT
• HYDROGEN WEAKLY BONDED TO UNSHARED ELECTRONDS IN
  ANOTHER MOLECULE
• HYDROGEN BONDING OCCURS BECAUSE THERE IS NO
  SHIELDING EFFECT AROUND HYDROGEN NUCLEUS

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IONIC COVALENT COMPOUND CHARACTERISTICS IONIC COVALENT COMPOUND CHARACTERISTICS IONIC COVALENT COMPOUND CHARACTERISTICS
Characteristics Ionic Compounds Covalent Compounds
Representative unit Formula Unit Molecule
Bond Formation Transfer of one or more electrons between atoms Sharing of electron pairs between atoms
Type of elements Metallic and non-metallic Non-metallic
Physical State Solid Solid, liquid or gas
Melting Point High (usually above 300 ?C) Low (usually below 300 ?C)
Solubility in water Usually high Usually low
Electrical conductivity of (aq) Good conductor Poor to non-conducting
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COVALENT BONDING

• THE END