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Covalent Electronegativity And Polarity Final
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Covalent Electronegativity And Polarity Final

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  • 1. Electronegativity and Polarity
  • 2. Electron Affinity
    • Measure of the tendency of an atom to attract electrons
    • Increases as atomic number increases in period
    • Decreases as you move down a group
    • Electronegativity
      • Indicates relative ability of an element’s atoms to attract electrons in a chemical bond
  • 3. Electronegativity
    • Not measure quantities…just numerical values assigned by Linus Pauling to compare the ability of atoms to attract shared electrons
    • Highest electronegative is F (3.98)
    • Lowest electronegative is Fr (0.7)
    • Noble gases generally do not form compounds
    • Exception: Larger noble gases (Xe, Rn)
    • Table on page 263
  • 4.  
  • 5. How we use electronegativity
    • Chemical bonds are never completely ionic or covalent because shared electrons are attracted to each other differently
    • Unequal sharing of electrons occurs because difference of electronegativities
    • Differences in electronegativity between two atoms can be used to predict the character and type of chemical bond formed between two atoms
  • 6.
    • Identical atoms have EN difference of zero
      • Electrons equally shared
      • Non-Polar Covalent bond (pure)
    • Polar Covalent Bonds
      • Unequal sharing of electrons between atoms of different elements
    • Ionic Bond
      • Large difference in EN between atoms indicates electron was transferred in a bond
    • Increase difference in EN  bond becomes more IONIC
    • EN difference 1.70 = 50% ionic and 50% covalent
    • EN difference >1.70 = IONIC
      • Exception: two nonmetals bonding
  • 7. POLAR COVALENT BONDS
    • Unequal sharing of electrons in a covalent bond
    • Tug-of-war
    • Electrons being shared spend more time around the EN atom than the other atom in the bond
    • Results in partial charges
      • δ + and δ -
      • POLARITY
    • More EN atom in the bond has the partially negative charge
    • Less EN atom in the bond has the partially positive charge
    • Dipole
      • Resulting polar bond between two different atoms in a covalent bond
  • 8.  
  • 9. Molecular Polarity
    • Polar molecules  attracted to electric field
    • Non-polar molecules  not attracted to electric field
    • Symmetrical molecular shapes  NON-POLAR (usually)
    • Asymmetrical molecules  POLAR as long as bond type is polar
  • 10.  
  • 11. Examples
    • Polar or non-polar molecules?
    • CCl 4
    • H 2 O
    • SCl 2
    • H 2 S
    • CF 4
    • CS 2
    • NH 3
  • 12. Solubility
    • Ability of one substance to dissolve in another substance
    • Physical property
    • Determined by bond type and shape
    • Polar molecules soluble in polar substances
    • Non-polar molecules soluble in non-polar substances
  • 13. Properties of Covalent Compounds
    • Salt vs. sugar
    • Difference in properties result in difference of attractive forces
    • Bond of atoms in covalent molecule is strong
    • Bond between covalent molecules is weak
    • Physical properties due to intermolecular forces…
  • 14. Intermolecular Forces
    • Weak attractive forces between individual molecules
    • Van der Waals Forces
      • Non-polar
        • Dispersion force or induced dipole
        • Very weak
      • Polar
        • Stronger than dispersion
        • Dipole-dipole force
        • Positive end of one dipole is attracted to negative end of another dipole
      • Hydrogen bond
        • Strongest intermolecular force
        • Formed between hydrogen of one dipole to the fluorine, oxygen, or nitrogen of another dipole
  • 15.  
  • 16. Physical properties
    • Low melting/boiling points
    • Many molecular substances are gases or vaporize readily at room temp
    • Hardness due to weak intermolecular forces (paraffin)
    • Solids form weak crystal lattice
  • 17. Covalent Network Solids
    • Solid in which atoms are interconnected by network of covalent bonds
    • Quartz
    • Diamond
    • Network solids are different from molecular solids
      • Brittle
      • Non-conductors of heat and electricity
      • Very Hard