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COVALENT BONDING AND POLARITY

COVALENT BONDING AND POLARITY. - POLARITY - INTERMOLECULAR BONDING. nonpolar covalent bonding -the electron pair is shared equally, ex. H 2 (g) -"tug of war" with equal partners. polar covalent bonding -when an electron pair is not shared

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COVALENT BONDING AND POLARITY

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  1. COVALENT BONDING AND POLARITY - POLARITY - INTERMOLECULAR BONDING

  2. nonpolar covalent bonding -the electron pair is shared equally, ex. H2(g) -"tug of war" with equal partners

  3. polar covalent bonding -when an electron pair is not shared equally, there is a localized negative charge around one atom, represented by the symbol δ-, while the other atom is more positively charged, δ+ - a polar covalent bond has a slightly negative end and a slightly positive end, ex. H2O, HCl (g)

  4. - polar molecules exhibit some ionic character! - whether a bond is polar covalent depends on the difference between the electronegativities of the bonded atoms

  5. Increasing Electronegativity Electronegativity - the measure of an atom's ability to attract the pair of electrons it shares with another atom within a covalent bond - increases up and right on periodic table -metals have a lower electronegativity then nonmetals

  6. Polar and Nonpolar Molecules polar molecules - molecules that have a positively charged end and a negatively charged end - the slight difference in charge within a covalent molecule is called a DIPOLE nonpolar molecules -do not have charged ends, ex. H2

  7. Polarity of a molecule depends on: • the presence of polar covalent bonds • the three-dimensional shape (geometry) of the molecule ex. ammonia, NH3(g): polar molecule because it contains polar covalent bonds and a pyramidal shape

  8. ex. methane, CH4(g) • nonpolar polar covalent bonds are all arranged symmetrically about the central carbon: symmetrical tetrahedral shape

  9. HOW DO WE KNOW WHAT TYPE OF BOND WILL FORM? - a bond difference of 0.4 or less is considered to be pure covalent [equal sharing of electrons] - a bond difference between 0.4 to 1.7 is considered to be polar covalent [unequal sharing of electrons] - a bond difference of 1.7 or greater is considered to be ionic [electrons were transferred] Increasing Electronegativity Difference 100% Slightly Polar Very 100 % Covalent Polar Covalent Polar Ionic Bonding

  10. In order to truly know if a substance is ionic or covalent, experimental data is needed to verify that the properties do apply!!!

  11. Polarity is closely related to intermolecular forces!!!

  12. Intermolecular Forces - weaker than covalent bonds, but can be stronger than ionic bonds - the temperature at which a liquid boils reflects the kinetic energy needed to overcome the attractive intermolecular forces (likewise, the temperature at which a solid melts)

  13. - intermolecular bonds are broken when a molecular compound melts and boils Thus, the strength of the intermolecular forces determines the physical properties of the substance

  14. 1. Hydrogen bonding -water is a highly polar molecule:the difference between the electronegativities of the oxygen and hydrogen atoms is 1.4, and the molecule is bent -since oxygen has the higher electronegativity, the electrons spend more time around oxygen than they do around hydrogen • the oxygen end of a water molecule has a slightly negative charge • the hydrogen end of the molecule is slightly positive

  15. -the arrangement of atoms and bonds forms a bent shape - the dipoles created by O-H in water are attracted to opposite charges creating hydrogen bonds: the strongest of all intermolecular forces

  16. - water is capable of dissociating ionic compounds

  17. 2) van der Waals forces -weak forces of attraction between molecules, such as the dipole–dipole force and the London dispersion force a) dipole–dipole force (DDF) -occurs between polar molecules, such as hydrogen chloride, HCl -the slightly positive end of one hydrogen chloride molecule is attracted to the slightly negative end of a neighbouring hydrogen chloride molecule

  18. b) London dispersion force (LDF) - an intermolecular force of attraction that forms between atoms of neighbouring molecules as a result of a temporary imbalance in the position of the atoms’ electrons -forms between all molecules, polar and nonpolar

  19. - the side of the atoms with more electrons develops a temporary negative charge, and the side with fewer electrons develops a temporary positive charge; if same happens to neighbouring molecule they attract each other - since electrons move quickly, the dipole lasts for only a fraction of a second

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