shapes of molecules

Question 1

What is the electron-pair repulsion theory?

Answer 1

+ An electron has a negative charge and therefore will repel each other therefore are arranged as far apart from each other as possible to minimise repulsion

Question 2

What shape and angles will a compound with 4 bonded pairs/4 bonding regions of electrons have?

Answer 2

+ Tetrahedral shape
+ Bond angle of 109.5*
+ The four electron pairs will repel equally

Question 3

What shape and angles will a compound with 2 bonding regions have?

Answer 3

+ Linear shape

+ Bond angle of 180*

Question 4

What is the difference between a bonded electron pair and a lone pair?

Answer 4

A lone pair of electrons will repel more than a bonded pair of electrons, this decreases the bond angle by 2.5* with each lone pair.

Question 5

What shape and angles will a compound have with two bonded pairs and two lone pairs?

Answer 5

+ Non-Linear shape

+ Bond angle of 104.5*

Question 6

What shape and angles will a compound have with three bonded pairs and one lone pair?

Answer 6

+ Shape: Pyramidal

+ Bond angle: 107

Question 7

What shape and angle will a compound have with three bonding regions?

Answer 7

Shape: Trigonal Planar
Angle: 120*

Question 8

What shape and angle will a compound with 6 bonding regions have?

Answer 8

+ Shape: Octahedral

+ Bond angle: 90*

Question 9

What shape and angle will a BF3 molecule have?
+
Draw the molecule

Answer 9

Has three bonding regions therefore a trigonal planar with 120* bond angle as all the electron pairs repel equally.

Question 10

What shape and bond angle will a SF6 molecule have?
+
Draw the molecule

Answer 10

Will have an octahedral shape with angle 90*

Question 11

What shape and angles will CH4 have?
+
Draw the shape

Answer 11

Will have the shape tetrahedral as it has four bonding regions and will have the bonding angle 109.5*

Question 12

What shape and angle will H2O have? Why does it have this bond angle?

Answer 12

H2O will have a non linear shape as it has 2 bonding regions and two lines pairs.
Therefore has angle 104.5* because it contains lone pairs and lone pairs will repel more than bonded pairs, therefore 109.5 - (2x 2.5)

Question 13

What shape and bond angle will an NH3 molecule have? And why?

Answer 13

NH3 will have a pyramidal shape because it has 3 bonding regions and one lone pair.
Lone pairs repel more than regular pairs therefore it will be 109.5 - 2.5* = 107* bond angle