intermolecular forces

Question 1

what are polar bonds?

Answer 1

covalent bonds can become polar if the atoms attached have difference in electronegativity

Question 2

what does the more electronegative atom do to electrons?

Answer 2

pulls electrons towards itself so it is delta negative

Question 3

how does a bond become more polar?

Answer 3

the bigger the difference in electronegativity the more polar a bond will be

Question 4

what charge does the most electronegative atom get ?

Answer 4

delta negative

Question 5

what charge does the least electronegative atom get ?

Answer 5

delta positive

Question 6

are atoms bonded with the same or similar electronegativitys polar ?

Answer 6

no
the shared electrons sit in the middle

Question 7

what is the strengths of intermolecular forces? strongest to weakest

Answer 7

hydrogen bonding
permanent dipole dipole
van der waals

Question 8

what do van der waals forces exist between?

Answer 8

atoms and molecules

Question 9

what can form a dipole when near another atom or molecule?

Answer 9

any molecule or atom with electrons can form a dipole when they move near to another atom or molecule

Question 10

how do the induced dipoles in van der waals occur?

Answer 10

this occurs as electrons in a molecule or atom can move from one end to another creating a temporary dipole

this temporary dipole only exists when 2 molecules or atoms are near by. when they move away the dipole interaction is destroyed

the delta positive on one atom or molecule will be attracted to the delta negative in another and a force of attraction is created

Question 11

how is the force of attraction created in the dipole? van der waals

Answer 11

the delta positive atom or molecule will be attracted to the delta positive on another and a force of attraction is created

Question 12

when can temporary dipoles only exist?

Answer 12

when 2 molecules or atoms are near by when they move away the dipole interaction is destroyed

Question 13

how does size of a molecule or atom effect van der waals forces?

Answer 13

the bigger the molecule or atom the more van der waals forces as there is larger electron clouds

Question 14

when we boil a liquid what is being broken?

Answer 14

when we boil a liquid we are breaking the weak van der waals forces not covalent bonds

we must have enough energy to overcome these forces

Question 15

how do van der waals forces hold iodine in its crystal structure?

Answer 15

weak van der waals forces holds the iodine molecules together

strong covalent bonds hold the 2 iodine atoms together

Question 16

how do van der waals forces act in crystal structures?

Answer 16

weak van der waals forces holds the molecules together

strong covalent bonds hold the atoms together

Question 17

do longer straight chain hydrocarbons have more van der waals forces or less?

Answer 17

they have more van der waals forces so more energy is needed to overcome these forces

so boiling point increases

Question 18

how does branching of hydrocarbons affect van der waals forces?

Answer 18

hydrocarbons with branches means they cant pack together as close

this weakens the van der waals forces between the chains and lowers boiling points

Question 19

what do permanent dipole dipole forces exist between?

Answer 19

dipole dipole interactions exist in molecules with a polarity

Question 20

what forces exist between molecules with a polarity ?

Answer 20

there are weak electrostatic forces that exist between molecules with a polarity

Question 21

why are dipole dipole stringer than van der waals forces?

Answer 21

dipole dipole interactions involves molecules with a permanent dipole so they are stronger as van der waals forces have induced dipoles

Question 22

molecules that have dipole dipole interactions also have ____________

Answer 22

van der waals forces too

Question 23

how can polar molecules e.g water be tested ?

Answer 23

they can be tested by placing a charged rod near a steady stream of polar liquid.

you should see the liquid bend towards the rod as the molecules allign to face the oppositely charged rod`

Question 24

what does hydrogen bonding occur between?

Answer 24

very electronegative elements

when hydrogen on one molecule forms a bond with the lone pair on nitrogen oxygen or fluorine

Question 25

what are the 3 most electronegative elements?

Answer 25

nitrogen oxygen or fluorine

Question 26

molecules that have hydrogen bonding also have ________________

Answer 26

van der waals and dipole dipole forces

Question 27

what structure does ice form?

Answer 27

ice forms a regular structure held together by hydrogen bonding

the molecules are further apart this makes ice less dense than water

Question 28

in H2o is oxygen delta + or -

Answer 28

oxygen is delta negative

Question 29

in H2o is hydrogen delta + or -

Answer 29

delta positive

Question 30

why does HF have a higher boiling point than HCL ?

Answer 30

HF has hydrogen bonding so more energy is needed to overcome the electrostatic forces

Question 31

what is the boiling point trend of hydrogen halides?

Answer 31

slight increase in boiling point from HCL to HI due to increased mass of molecule hence bigger electron cloud and more van der waals forces