Uneven sharing results in charged ends of molecules
Water is an example of a polar covalent molecule. The charged ends of the molecule make water sticky, give it a high boiling point, and are the reason snowflakes are shaped the way they are
FYI: clarification! (not on the test!)
Look at the electronegativity difference between boron and fluorine to predict the bond type in BF 3 .
Predictions based on this “rule” say this should be an ionic compound, but in the lab, it has been determined that this bond is actually very polar covalent.
The diagram on the left of page 176 is instructive. This suggests the is actually not a fixed rule with a LINE to separate that .3 and 1.7, but rather a “shades of gray” (or blue and green!) situation.
Conclusion? This is a guideline, but the lab is the only way to definitively establish bond type.
Intermolecular attractions between particles
Dipole-Dipole forces: occur between polar molecules
Hydrogen bonding: a type of dipole-dipole force in which a hydrogen atom in a polar bond is attracted to the electronegative end of another polar molecule
London dispersion forces: instantaneous tiny dipoles created in collisions between non-polar molecules or noble gas atoms
Comparing ionic and covalent bonds
Ionic bonds dissociate in solution
Ionic substances conduct when in solution or molten
Covalent bonds are stronger than ionic bonds
Covalent substances melt and boil at LOWER temperatures than ionic. WHY?
A group of covalently bonded atoms working together as a single ion
Example: the hydroxide ion, OH -
The oxygen and hydrogen are covalently bonded, but together have 10 electrons and 9 protons, for a net charge of -1. They stick together, bonding as a single ion in compounds like KOH, an ionic compound. KOH dissociates into K + and OH - in solution.
See chart on window wall for more polyatomic ions.
Vocabulary: Sea of electrons
How do the properties of metals result from the metallic bond?
We usually don’t contrast metallic bonds with ionic and covalent; they could be generally considered a subgroup of covalent bonds due to their , but they don’t form molecules. They’re just different. Be aware of them, but the ionic/covalent differences are of greater importance.