molecular geometry and imf Flashcards
chem unit 3 part 2
vsepr theory
VSEPR stands for valence shell electron pair repulsion. Depending on the amount of bonding pairs, the degree of separation between the electron pairs will differ. The unshared pairs strongly repel bonding pairs, which push them closer together.
electronegativity
the ability of an atom to attract electrons in a bond
dipole moment
when unequal sharing of electrons due to differences in electronegativities cause partial chargers on each atom/end of molecule
how is the strength of a dipole moment determined
the difference in electronegativity between the atoms involved in a bond; the larger the electronegativity difference, the stronger the dipole moment is, essentially meaning the greater the separation of charge within the molecule
polar covalent bonds
a bond with a permanent dipole moment
nonpolar covalent bonds
equal sharing of electrons; no dipole moment
difference between polar and nonpolar covalent bonds
polar has a permanent dipole moment, nonpolar does not but has equal sharing of electrons
3 types of intermolecular forces (IMF)
london (dispersion) forces,
dipole-dipole forces, and hydrogen bonding
london (dispersion) forces
LD forces are present to an extent in all molecules and atoms; they are caused by fluctuations in the electron distribution
-weak
dipole-dipole forces
dipole-dipole forces exist in all polar molecules; polar molecules have permanent dipoles that interact with permanent dipoles of neighboring
molecules
-moderate
hydrogen bonding
hydrogen bonding occurs in polar molecules containing H bonded to F, O, or N; very strong dipole-dipole force; this is the strongest type of IMF due to the large electronegativity difference between the atoms,
as well as the small size of the atoms (which allows neighboring molecules to get very close to
each other)
-strong
rank the relative strengths of the intermolecular forces
london (dispersion) forces < dipole-dipole forces < hydrogen bonds
explain why a substance has a higher melting/boiling point due to molar mass
and/or strength of IMFs
as molar mass increases, the magnitude of the dispersion forces increases (in general), thus, larger molecules/atoms have higher boiling points
ionic bond
if the difference in electronegativity is more than 2.0, the electrons will likely be pulled away completely by one of
the atoms, called an ionic bond
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non-polar covalent
