Covalent Electronegativity And Polarity Final


Published on

Published in: Technology, Education
1 Like
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Covalent Electronegativity And Polarity Final

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