structure and bonding Flashcards
covalent bonds
atoms share pairs of electrons, positive nuclei held by common attraction for share electrons, usually non-metal atoms
polar covalent
medium difference in electronegativity values, and/or unsymmetrical molecular shape
permanent dipole (polar partial charges)
atoms with higher electronegativity is delta -, atoms with lower electronegativity are delta +
ionic bonds
electrostatic attraction between + and - ions
ionic compounds
form lattice structures of oppositely charged ions
bonding continuum
electronegativity
small/no difference - pure covalent
medium difference - polar covalent
large difference - ionic bonding
ion electrons arrangement
atoms w/ lower electronegativity transfer electrons to atom w/ larger electronegativity value to form ions
melting points
ionic - high
covalent networks - high
covalent molecular - low
room temperature state
ionic - solid
covalent network - solid
covalent molecular - all gas/liquid compounds
solubility
ionic compounds and polar covalent substance soluble in water as it is also polar.
non-polar substances more likely to be soluble in non-polar solvents.
electrical conductivity and bonding
metallic - solid, liquid, not applicable in solution
covalent - none
ionic - liquid and in solution
intermolecular forces
found between all atoms, molecule and compounds in every state
van der waals
London Dispersion Forces (LDFs)
Permanent dipole- permanent dipole interactions (pd-pd)
hydrogen bonding (FON)
London DIspersion Forces
between all atoms and molecules, weaker than other bonding types.
caused by temporary uneven electron distribution causing temporary dipoles which is then induced on neighbouring atoms.
LDF strength
greater number of electrons = stronger LDF
larger molecules = stronger LDF
permanent dipoles
found in polar molecules
pd-pd interactions
permanent dipoles in each molecule attracted to each other
additional electrostatic forces of attraction (on top of london dispersion forces)
symmetry and polarity
symmetrical - non-polar even if contains polar bonds
unsymmetrical - polar
bonding strength
LDF < pd-pd < hydrogen bonding < ionic and covalent bonding
hydrogen bonds
electrostatic forces of attraction found between molecules containing -
-OH, -NH, H-F
-OH - water, alcohols, carboxylic acids
-NH - ammonia, amines
high melting and boiling points
stronger intermolecular forces are
covalent compounds with hydrogen bonding
higher melting points, boiling points and viscosity than those with LDFs
polar molecules -> non polar
stronger intermolecular forces when comparing molecules with similar electron numbers
viscosity
hydrogen bonding - thicker
pd-pd - medium
LDF - thinner
ice density
less than water due to hydrogen bonding expanding structure of ice compared to liquid water, unlike most substances its solid floats in its liquid