mr allen test mod2- dipoles

Question 1

shapes of molecules: how many bonds doe a double bond count for?(odd)

Answer 1

1 (c=c)= 1 bond

Question 2

if a molecule has 2 bond electron pairs, state its shape and bond angle

Answer 2

linear, 180

Question 3

if a molecule has 3 bond electron pairs, state its shape and bond angle

Answer 3

trigonal planar, 120

Question 4

if a molecule has 4 bond electron pairs, state its shape and bond angle

Answer 4

tetrahedral, 109.5

Question 5

if a molecule has 6 bond electron pairs, state its shape and bond angle

Answer 5

octahedral, 90

Question 6

shapes of molecules, why is O2 an exception, why isn’t it linear??

Answer 6

there are two lone pairs, as a result of extra repulsion, bond angles tend to be slightly less and the bonds are squeezed together

Question 7

why does NH3 not have a trigonal planar shape

Answer 7

• it has 3 bond pairs and 1 lone pair so the shape is based on a tetrahedral ( bond angles go from 109.5 to 107)

Question 8

what is oxygens shape based on? ( it isn’t linear)

Answer 8

-4 total bonds (2 lone, 2 bonding pairs) so tetrahedral

Question 9

how much do you minus for every lone pair?

Answer 9

2.5

Question 10

why are intermolecular forces weak

Answer 10

as it takes not a lot of energy for them to break unlike strong covalent bonds- however if there are a lot of covalent bonds, a lot of energy is required.

Question 11

what are physical forces?

Answer 11

the forces between different molecules within a substance (intermolecular forces), there are 3 different types of physical forces.

Question 12

what are the three types of physical forces (weakest to strongest)

Answer 12

induced dipole-dipole interactions(london forces)
permanent dipole dipole interactions
hydrogen bonds

Question 13

describe induced dipole-dipole interactions( london forces)

Answer 13

• at any instant in time, it is possible that more electrons will lie to one side of the atom/molecule than the other An instantaneous dipole is produced. this induces weak dipole in nearby atoms/molecules. this creates weak forces between atoms/molecules. (helium example)

Question 14

describe what happens when size of a molecule/ atom increases and there are more electrons (london)

Answer 14

boiling point increases as the size of the molecule/atom increases, this is because as the sizes of the atoms/ molecules increase and there are more electrons, the size of the induced dipole dipole interaction forces increase, thus more energy required to break stronger forces.

Question 15

what is electronegativity?

Answer 15

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

Question 16

describe trend of electronegativity on periodic table…

Answer 16

as you go up and across, electronegativity increases.

Question 17

talk about permanent dipole-dipole interactions(why do they occur in terms of electrons)- how do polar covalent bonds FORM

Answer 17

electrons in a covalent bond on average spend their time nearer to one of the 2 bonded atoms. That atom gains a small negative charge. the other atom gains a small positive charge, this produces a polar covalent bond

Question 18

what is the most electronegative atom

Answer 18

Fluorine

Question 19

simmilar atoms have simmilar electronegativity and so molecules will be non polar, give an example of a non polar molecule

Answer 19

carbon and hydrogen

Question 20

when atoms have a difference in electronegativity, what is formed?

Answer 20

a polar molecule ( difference in polarity in a dipole)

Question 21

polar molecules???

Answer 21

often occur within molecules, we must consider the remaining bonds and shape of the molecule to determine if the molecule itself will be polar.

Question 22

is co2 polar or non polar

Answer 22

non-polar but made up of polar bonds

Question 23

what are the rules if a molecule is polar or non polar?

Answer 23

• molecules are polar id they contain bonda and are asymmetric
• if a molecule contains polar bonds but is symmetrical, its non polar.

Question 24

what is the movement of symmetrical

Answer 24

no net movement

Question 25

why is water polar

Answer 25

not a symmetrical molecule, net upwards movement

Question 26

why is co2 non polar

Answer 26

overall, dipoles cancel (tug of war). non-polar but made of polar bonds.

Question 27

what are polar molecules held by

Answer 27

by dipole-dipole interactions (2nd type)

Question 28

talk about occurrence of dipole-dipole interactions “2”

Answer 28

between molecules containing polar bonds in addition to the basic induced dipole-dipole forces.
the extra attraction between dipoles mean that more energy must be used to separate molecules.
get higher melting/boiling points that expected given mass

Question 29

what is the 3rd imf ( hydrogen bonding) a version of

Answer 29

permanent dipole-dipole

Question 30

what is hydrogen bonding exclusive to

Answer 30

F,O,N

Question 31

Talk about hydrogen bonding

Answer 31

strongest imf
water is highly polar due to large difference in electronegativity between o and h
this results in a very strong dipole-dipole attraction called a hydrogen bond between water molecules.
can occur between molecules containing H,F,O,N atoms as N,O,F have high electronegativity and H has a low electronegativity,

Question 32

what are the features of drawing hydrogen bonding?

Answer 32

• lone pairs on O,N,F
• partial charges on atoms
• dashed line for hydrogen bonds and solid bond for covalent bonds.

Question 33

water has a high melting/ boiling point, explain why?

Answer 33

the strong H bonds need to be broken which requires more energy tan other imfs

Question 34

ice floats on water, explain…

Answer 34

the long H bonds hold water molecules apart in lattice structure giving it a larger volume in liquid water

Question 35

water has a high surface tension and viscosity, explain

Answer 35

the string H bonds need to be broken

Question 36

what is the shape and angle of a molecule with 3 bond pairs and one lone pair

Answer 36

pyramidal

107 degrees

Question 37

Give an example of a simple covalent molecule which has all bond angles equal to 90°

Answer 37

SF6

Question 38

Give an example of a simple covalent molecule which has all bond angles equal to 180 degrees

Answer 38

CO2