1.3 bonding- polarity Flashcards
electronegativity definition
the ability of an atom to attract a bonding pair of electrons in a covalent bond
trend in electrogenativity across a period
increases
-more protons in nucleus
-decreasing atomic radius
-same amount of shielding
so bonding pair is easier to attract
trend in electronegativity down a group
decreases
-increasing atomic radius
-more shielding
so bonding pair is harder to attract
what is a polar bond/polar covalent bond
covalent bond where the electron distribution is uneven so there’s an unequal sharing of electrons
-the greater the difference in EN, the more polar the bond
when is a bond purely covalent
when 2 atoms have the same EN
when is a bond ionic
when there is a large difference in EN
why is CO2 a nonpolar molecule despite having polar bonds (3)
-carbon and oxygen have different EN
-CO2 has a linear shape, so the 2 polar bonds are symmetrical
-the 2 polar bonds cancel, out forming a non polar molecule
state the strength of each intermolecular force
-hydrogen bonding is strongest
-van der waals is weakest
-all IMF are weaker than covalent bonds
how does a permanent dipole-dipole force occur eg. HCl (4)
-chlorine is more EN than hydrogen
-shared pair of electrons is more attracted to chlorine
-creates a permanent dipole
-δ+ on one molecule attracts δ− on an adjacent molecule
which IMF exists in non-polar molecules
van der waals
how do van der waals forces occur (4)
-form due to uneven distribution of electrons
-leads to a temporary dipole, which causes an induced dipoles on adjacent molecules
-these dipoles attract
-greater number of electrons=stronger attractive force
which molecules do hydrogen bonds exist between
molecules which contain a F-H, O-H or N-H bond
how does hydrogen bonding occur in water (3)
-oxygen is more EN than hydrogen
-so the bond is very polar
-there is an attraction between the δ+H in one molecule and the lone pair of electrons on the oxygen in an adjacent molecule
rules for hydrogen bonding
-hydrogen must be directly covalently bonded to an electronegative enough atom (N, O ,F)
-must be an available lone pair on the EN atom
why does HF have a much higher boiling point than HCl
-HF has hydrogen bonding, HCl has VDW
-hydrogen bonds are stronger so more energy needed to overcome
