chapter 6

Question 1

why do molecules have a 3D shape?

Answer 1

because pairs of electrons repel to be as far apart as possible

Question 2

what is the name of the shape of a molecule that has two regions?

Answer 2

linear

Question 3

what is the bond angle in a molecule that has two regions (linear)?

Answer 3

180 degrees

Question 4

what is the name of the shape of a molecule that has three regions?

Answer 4

trigonal planar

Question 5

what is the bond angle in a molecule that has three regions (trigonal planar)?

Answer 5

120 degrees

Question 6

what is the name of the shape of a molecule that has four regions?

Answer 6

tetrahedral

Question 7

what is the bond angle in a molecule that has four regions (tetrahedral)?

Answer 7

109.5 degrees

Question 8

what is the name of the shape of a molecule that has five regions?

Answer 8

trigonal bipyramidal

Question 9

what is the bond angle in a molecule that has five regions (trigonal bipyramidal)?

Answer 9

120 and 90 degrees

Question 10

what is the name of the shape of a molecule that has six regions?

Answer 10

octahedral

Question 11

what is the bond angle in a molecule that has six regions (octahedral)?

Answer 11

90 degrees

Question 12

what happens to the shape of a molecule if it has lone pairs?

Answer 12

lone pairs repel more because they are slightly closer to the central atom so changes the shape

Question 13

what is the name of the shape of the molecule that has three regions and a lone pair?

Answer 13

pyramidal

Question 14

what is the bond angle of a molecule with three regions and a lone pair?

Answer 14

107 degrees

Question 15

what is the name of the shape of the molecule that has two regions and two lone pairs?

Answer 15

non-linear

Question 16

what is the bond angle of a molecule with two regions and two lone pairs?

Answer 16

104.5 degrees

Question 17

why do lone pairs reduce the bond angle?

Answer 17

lone pairs push bonded pairs slightly closer together (so take away 2.5 degrees for each lone pair)

Question 18

what is electronegativity?

Answer 18

measure of the ability of an atom in a molecule to attract a pair of electrons

Question 19

what are the most electronegative elements?

Answer 19

F
O
Cl

Question 20

what does the higher the electronegativity value mean?

Answer 20

the more strongly the bonded electrons are attracted to that atom

Question 21

what happens to the electronegativity as the number of protons increases?

Answer 21

the pulling on bond electrons increases due to increased nuclear charge

Question 22

how can distance also effect electronegativity?

Answer 22

the greater the distance from the nucleus the lower the pull on shared electrons despite having a higher nuclear charge

Question 23

what does it mean if a molecule is non-polar?

Answer 23

bonded atoms are the same or have the same/similar electronegativity value

Question 24

what is a non-polar bond?

Answer 24

bonded electron pair is shared equally between the bonded atoms

Question 25

what does it mean if a molecule is polar?

Answer 25

bonded electron pair is shared unequally between bonded atoms

Question 26

what does the delta sign mean?

Answer 26

partial charge

Question 27

what is a dipole?

Answer 27

separation of opposite charges in a molecule

Question 28

how can something contain polar bonds but not be a polar molecule overall?

Answer 28

polar bonds/dipoles cancel out

Question 29

when do polar bonds/dipoles cancel out to make a non-polar molecule?

Answer 29

if there is a line of symmetry

Question 30

why does water (polar molecule) dissolve things?

Answer 30

polar molecules can form strong enough attractions to permit dissolving

Question 31

what is an example of why a molecule is polar?

Answer 31

if there are lone pairs then the bond angle is not symmetrical so the molecule is polar

Question 32

what are intermolecular forces?

Answer 32

weak interactions between molecules

Question 33

what are london forces?

Answer 33

instantaneous dipoles attracted to each other
the weakest type of intermolecular force and exist between all molecules

Question 34

how are instantaneous dipoles formed?

Answer 34

electrons in an atom move constantly
temporary uneven distribution of electrons forms an instantaneous dipole

Question 35

how do instantaneous dipoles form and become attracted to each other?

Answer 35

instantaneous dipole induces a dipole in its neighbour
these dipoles are attracted together due to opposite charges

Question 36

what are permanent dipole-dipole intercations?

Answer 36

formed when molecules which are polar interact
opposite dipoles attract to each other
(full time strong forces)

Question 37

what are hydrogen bonds?

Answer 37

specific type of permanent dipole-dipole interaction

Question 38

what do hydrogen bonds need to form?

Answer 38

electronegative atom with a lone pair of electrons (O, N, F)
hydrogen atom attached to that electronegative atom (H-O, H-N, H-F)

Question 39

why is ice less dense than water?

Answer 39

hydrogen bonds hold water molecules apart in an open lattice structure
water molecules are further apart in ice than in water

Question 40

why do molecules with hydrogen bonds have high melting/boiling points?

Answer 40

strongest type of weak bond
more energy is needed to break the bonds