shapes of molecules

Question 1

what is the charge of an electron

Answer 1

negative

Question 2

why do groups of electrons repel each other

Answer 2

electrons are negatively charged so they repel each other and they arrange themselves to be as far away from each other in space as possible

Question 3

why do electron pairs arrange themselves to be as far away from each other as possible

Answer 3

to minimise repulsion

Question 4

what determines the shape of simply covalently bonded substances

Answer 4

electron pair repulsion theory

Question 5

what is the electron pair repulsion pair theory

Answer 5

the shape of a molecule is determined by the number of groups of electrons around the central atom. the groups might be a non bonding or bonding pair of electrons. these electron groupings repel to make the angles between them as wide as possible

Question 6

what are the different repelling effects

Answer 6

bonding pair/bonding pair
bonding pair/lone pair
lone pair/lone pair

Question 7

which pairs cause the most repulsion

Answer 7

lone pair/lone pair

Question 8

what does the straight line in a 3D shape represent

Answer 8

represents a bond in the plane of the paper

Question 9

what does the dashed line in a 3D shape represent

Answer 9

a bond in the direction behind the plane of the paper

Question 10

what do the wedged lines in a 3D shape represent

Answer 10

a bond in the direction in front of the plane of the paper

Question 11

what is the shape and angle of two bonding pairs

Answer 11

linear - bond angle 180°

Question 12

BeF₂ - bond angle and shape

Answer 12

consider the central atom - Be is in group 2 so has 2 outer electrons
in bonding each outer atom contributes 1 electron
so fluorine donates 2 electrons altogether
2xF = 2e-
Be = 2e-
4e - = 2 pairs
so LINEAR BOND ANGLE 180°

Question 13

what is the bond angle and shape of 3 bonded pairs

Answer 13

trigonal pair 120°

Question 14

BF3 bond angle and shape

Answer 14

3 x F = 3e-
B is in group 3 so 3e-
3 + 3 = 6e-
6e- = 3 pairs
so TRIGONAL PLANAR 120°

Question 15

what is the bond angle and shape of 4 bonding pairs

Answer 15

tetrahedral 109.5°

Question 16

CCl4 bond angle and shape

Answer 16

4 x Cl = 4e-
C is in group 4 so 4e-
4 + 4 = 8e-
8e- = 4 pairs
TETRAHEDRAL 109.5°

Question 17

what is the bond angle and shape of 5 bonding pairs

Answer 17

trigonal bipyramid 120° and 90°

Question 18

PF5 bond angle and shape

Answer 18

5 x F = 5e-
P is in group 5 so 5e-
5 + 5 = 10e-
10e- = 5 pairs
TRIGONAL BIPYRAMID 120° and 90°

Question 19

what is the bond angle and shape of 6 bonding pairs

Answer 19

octahedral 60°

Question 20

SF6 bond angle and shape

Answer 20

6 x F = 6e-
S in group 6 so 6e-
6 + 6 = 12e-
12e- = 6 pairs
OCTAHEDRAL 90°

Question 21

what is the shape and bond angle of 3 bonded pairs and 1 lone pair

Answer 21

trigonal pyramid - bond angle 107°

Question 22

NH3 bond angle and shape

Answer 22

N = group 5 so 5e-
H x 3 = 3e-
3 + 5 = 8e-
8e- = 4 pairs
there are only 3 electron bonded pairs (4-3=1)
so 1 lone pair
TRIGONAL PYRAMID - 107°

Question 23

what is the shape and bond angle of 2 bonded pairs and 2 lone pairs

Answer 23

bent 104.5°

Question 24

H₂O shape and bond angle

Answer 24

O = group 6 = 6e-
H x 2 = 2e-
8e- = 4 pairs
only 2 bonded pairs so must be 2 lone pairs
BENT 104.5°

Question 25

what do lone pairs give

Answer 25

extra repulsion

Question 26

why are double and triple bonds considered to be single bonds

Answer 26

for repulsion purposes

Question 27

what determines the shape

Answer 27

groups of electrons NOT THE NUMBER OF ELECTRON PAIRS

Question 28

what does it mean by electron density

Answer 28

concentration of electrons in one area

Question 29

how many regions of electron density in C2H4 and why

Answer 29

3 regions of electron density at each carbon
- double bond is 1 area
- two C-H bonds is 2 areas

Question 30

3 regions of electron density = ..

Answer 30

trigonal bipyramid

Question 31

suggest a value for the HCH bond angle in ethene and explain this in terms of electron pair repulsion theory

Answer 31

3 areas of electron density around the central carbon atom. these areas repel each other and move as far away from each other as possible in order to minimise repulsion. this gives it the shape trigonal bipyramid with bond angle 120°

Question 32

how do we work out the shapes of ions

Answer 32

include any extra electrons that have been added or taken away
- add one electron for -ve charge
- take away one electron for +ve charge

Question 33

NH4+ bond angle and shape

Answer 33

N = group 5 so 5e-
H x 4 = 4 e-
9e-
but you take away one e- to give 8e-
8e- = 4 pairs
TETRAHEDRAL 109.5°

Question 34

NH2- bond angle and shape

Answer 34

N = 5e-
H x 2 = 2e-
= 7e-
add one electron so 8e-
8e- = 4 pairs
2 are bonded so 2 must be lone
BENT 104.5°