CHE 110 Study Guide - Midterm Guide: Boiling Point, Glycerol, Evaporation
Objective #9:
Polarity: polar bonds can give you a polar molecule with a dipole moment for the molecule
• Creates a sort-of partial +/- charge within the molecule
• Equal sharing = nonpolar, Unequal sharing = polar
• Electronegativity difference 0-.4 same EN, .5-2.0 then continuum
• The Geometry of the molecule affects the polarity, need an uneven distribution
of e-
• Polar bonds cancel each other out and no overall dipole is created
Metals: found on the left side of the stair-step line, tend to lose e- and for positive ions
Non-Metals: found on the right side of the stair-step line, tend to gain e- and form negative ions
Covalent Bond: atoms share electrons in order to satisfy the octet rule (8 ve-)
• Ex: CH4
• Have lower melting points and tend to be liquids and gases
• Don’t have organized structures
• Two atoms share at least 2 e- to get to their 8e- (besides Hydrogen and Helium which
want 2e-)
Ionic Bond: forms when atoms are held together by the attraction between opposite charges
• Ex: NaCl
• Have crystallized structures
• Conduct electricity if soluble in water
• One atom is much stronger than the other
• Electronegative difference is greater than 2.0 (on average)
Intermolecular Forces: the forces between molecules, ability of the compound to stick to
itself/each other
1) Dipole-Dipole: force with 2 ends (- and +) that pull polar molecules together
2) Hydrogen Bonds: really strong dipole-dipole force, molecule has to have OH, NH, or FH
to bond
3) London Dispersion Force: forces pulling non-polar molecules, attraction because of mass
Close particles → Farther particles
(Endo → Exo )
heat of vaporization: liquid to gas (endothermic)
heat of fusion: solid to liquid (endothermic)
Examples of Endothermic:
Baking cookies, melting solids, splitting molecules
Examples of Exothermic:
Making ice cubes, formation of snow, burning sugar, rusting iron, a candle flame
Study and know how to use the chart
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