1.3 bonding- polarity Flashcards

1
Q

electronegativity definition

A

the ability of an atom to attract a bonding pair of electrons in a covalent bond

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2
Q

trend in electrogenativity across a period

A

increases
-more protons in nucleus
-decreasing atomic radius
-same amount of shielding
so bonding pair is easier to attract

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3
Q

trend in electronegativity down a group

A

decreases
-increasing atomic radius
-more shielding
so bonding pair is harder to attract

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4
Q

what is a polar bond/polar covalent bond

A

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

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5
Q

when is a bond purely covalent

A

when 2 atoms have the same EN

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6
Q

when is a bond ionic

A

when there is a large difference in EN

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7
Q

why is CO2 a nonpolar molecule despite having polar bonds (3)

A

-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

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8
Q

state the strength of each intermolecular force

A

-hydrogen bonding is strongest
-van der waals is weakest
-all IMF are weaker than covalent bonds

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9
Q

how does a permanent dipole-dipole force occur eg. HCl (4)

A

-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

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10
Q

which IMF exists in non-polar molecules

A

van der waals

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11
Q

how do van der waals forces occur (4)

A

-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

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12
Q

which molecules do hydrogen bonds exist between

A

molecules which contain a F-H, O-H or N-H bond

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13
Q

how does hydrogen bonding occur in water (3)

A

-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

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14
Q

rules for hydrogen bonding

A

-hydrogen must be directly covalently bonded to an electronegative enough atom (N, O ,F)
-must be an available lone pair on the EN atom

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15
Q

why does HF have a much higher boiling point than HCl

A

-HF has hydrogen bonding, HCl has VDW
-hydrogen bonds are stronger so more energy needed to overcome

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16
Q

why does BP increase from Hcl to Hbr to HI

A

-halogens increase in size
-VDW are stronger down the group so more energy needed to overcome

17
Q

why does CBr4 have a higher BP than CHBr3 (3)

A

-CBr4 has VDW, no dipoles
-CHBr3 has VDW and dipole-dipole
-CBr4 VDW are stronger as molecule is bigger

18
Q

why does nonane have a higher BP than 2-4-dimethylheptane (2)

A

-nonane has more VDW
-nonane molecules pack closer together and have mores surface contact