Shapes of Molecules

Question 1

What is valence shell electron-pair repulsion theory

Answer 1

Electron pairs around central atom repel each other and get as far apart as possible from each other to minimise this repulsion which can be used to predict shapes and bond angles of molecules

Question 2

What does a bold wedge mean

Answer 2

Bond coming out of paper

Question 3

What does dotted wedge mean

Answer 3

Bond going into paper

Question 4

Shape and bonding angle in molecule with two bonding pairs

Answer 4

Linear, 180 degrees

Question 5

Shape and bonding angle in molecule with three bonding pairs

Answer 5

Trigonal planar, 120 degrees

Question 6

Shape and bonding angle in molecule with four bonding pairs

Answer 6

Tetrahedral, 109.5 degrees

Question 7

Shape with description and bonding angle in molecule with five bonding pairs

Answer 7

Trigonal bipyramidal(two triangle based pyramids base to base), bonding angles are 90 120 degrees

Question 8

Shape with description and bonding angles in molecule with six bonding pairs

Answer 8

Octahedral(two square based pyramids base to base), bond angles 90 and 180 degrees

Question 9

By how many degrees does each lone pair reduce the bond angle by

Answer 9

By 2.5 degrees

Question 10

How do double and triple bonds affect bond angle

Answer 10

They do not affect it as they are treated as single bonds, just called areas of electron density

Question 11

Order of strength of repulsion and why

Answer 11

lp-lp repulsion > lp-bp repulsion > bp-bp repulsion
-this is because lone pairs are closer to the nucleus so are more compact so repulsion stronger

Question 12

Shape and bond angle in molecule with three bps and one lp

Answer 12

Trigonal pyramidal, bond angle 107 as it is same shape as tetrahedral but with lone pair

Question 13

Shape and bond angle in molecule with 2 bps and 2 lps

Answer 13

Bent, bond angle 104.5 as lps treated as atoms so is tetrahedral minus 2 x 2.5 degrees