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Two Types of Forces• Intra Molecular Forces - The forces of
attraction that exist within a molecule.• Inter Molecular Forces - The forces of
attraction (or repulsion) between a molecule and a neighboring molecule
Electronegativity and Polarity
• Electronegativity - the tendency of an atom to draw electrons in a bond toward itself
• There are two periodic trends concerning electronegativity.x As you move down a group, electronegativity decreasesx As you move across a period, electronegativity increases
Polarity - Polar• Not all electrons are shared equally…• Polar covalent- unequal sharing of e-
between two atoms (kind of like tug-of-war)
• The atom with greater electronegativity will hog the electronsx Symbol:
x δ+ (positive end of molecule) x δ- (negative end of molecule)
x All bent and pyramid shapes are polar
Polarity - Nonpolar• Nonpolar covalent - covalent bond in
which the electrons are shared equallyx Ex. The diatomic elements (Br, I, N, Cl, H, O,
and F) are all have nonpolar covalent bonds
x Cl – Cl Br – Br I – I
x N – N H – H O – O F – F
Calculating Polarity• Polarity can be determined by the
difference in electronegativities of the atoms (EN) x Trend: Increasing EN to the right and up
Calculating Polarity• Determine if the following bonds are polar
or nonpolar. (If polar, label δ+ or δ-)• F – F
• O – C
• C – H
Intermolecular Forces• Intermolecular Forces (IMF) -attraction between molecules
• Three types (Van der Waals Forces)x Dipole-Dipolex Hydrogen Bondsx London Dispersion
Dipole - Dipole• The positive dipole of one polar molecule is attracted to the negative dipole of another moleculex Ex. H - Cl is polar, the negative Cl is
attracted to the positive H on ANOTHER molecule
Hydrogen Bonding• The attraction between an H atom and
unshared electrons on N, O, or F (on a different molecule)
• H – F or H – O or H– Nx STRONG attraction (important to life)
• Ex. H2O attracts H2O
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