3.1.3.5 Shapes of simple molecules and ions

Question 1

the bond angle found in an ammonia molecule

Answer 1

107°

Question 2

why the bond angle in an amide ion is smaller than that in an ammonia molecule

Answer 2

More lone pairs on NH2 – , than on NH3

Lone pairs repel more than bonding pairs M

Question 3

value for the H−O−O bond angle in hydrogen peroxide

Answer 3

94−105.5°

Question 4

Definition: electronegativity

Answer 4

The power of an atom or nucleus to withdraw or attract electrons OR electron density OR a pair of electrons (towards itself) Ignore retain
In a covalent bond

Question 5

why the electronegativity of the elements increases from lithium to fluorine

Answer 5

More protons / bigger nuclear charge

Same or similar shielding / electrons in the same shell or principal energy level / atoms get smaller

Question 6

Name of the shape made by the three atoms in the NH2 – ion

Answer 6

Bent / v shape/ triangular

Question 7

reason why neon does not form compounds with sodium

Answer 7

Ne has full sub-levels/ can’t get any more electrons in the sub-levels/ Ne has full shells

Question 8

value for the F—N—F bond angle in NHF2

Answer 8

107°

Question 9

the bond angle in the PH4 + ion

Answer 9

109.5° / 109½ / 109°

Question 10

value for the bond angle in the H3O+ ion

Answer 10

107°

Question 11

one molecule with the same number of atoms, the same number of electrons and the same shape as the H3O+ ion

Answer 11

NH3/ammonia

Question 12

the number of lone pairs of electrons in the hydroxide ion

Answer 12

3

Question 13

the bond angle in the BF4 – ion

Answer 13

109° to 109.5°

Question 14

Predict the shape of the ion. Explain why it has this shape.

Answer 14

Tetrahedral
(Equal) repulsion
between four bonding pairs / bonds

Question 15

why the bond angles in the NH4 + ion are all 109° 28’

Answer 15

4 bonding / electron pairs
repel equally
as far apart as possible
tetrahedron

Question 16

Name of shape of NHF2

Answer 16

pyramidal / trigonal pyramid

Question 17

Name of shape of BF3

Answer 17

trigonal planar

Question 18

value for the F—N—F bond angle in NHF2

Answer 18

107°

Question 19

the shape of CCl2

Answer 19

Bent / v shape

Question 20

Explain how the electron pair repulsion theory can be used to deduce the shape of, and the bond angle in, PF3

Answer 20

Stage 1: Electrons round P
• P has 5 electrons in the outside shell
• With 3 electrons from 3 fluorine, there are a total of 8 electrons in outside shell
• so 3 bond pairs, 1 non-bond pair
Stage 2: Electron pair repulsion theory
• Electron pairs repel as far as possible
• Lone pair repels more than bonding pairs
Stage 3: Conclusions
• Therefore, tetrahedral / trigonal pyramidal shape
• With angle of 109(.5)° decreased to 107°

Question 21

reason why electron pair repulsion theory cannot be used to predict the shape of the [CoCl4] 2− ion

Answer 21

Too many electrons in d sub-shell / orbitals

Question 22

Predict the shape of, and the bond angle in, the complex rhodium ion [RhCl4] 2− .

Answer 22

Tetrahedral (shape)

109.5°

Question 23

why the AsCl4 + ion has a bond angle of 109.5°.

Answer 23

There are 4 bonds or 4 pairs of electrons (around As)

(Electron pairs / bonds) repel equally

Question 24

the bond angle found in an ammonia molecule

Answer 24

107°

Question 25

why the bond angle in an amide ion is smaller than that in an ammonia molecule

Answer 25

More lone pairs on NH2 – , than on NH3

Lone pairs repel more than bonding pairs

Question 26

Why is each bond angle exactly 120° in BCl3

Answer 26

3 (bonding) pairs of electrons

Question 27

Predict the bond angle in CCl2 and explain why this angle is different from that in BCl3

Answer 27

Predicted bond angle: 118° (allow 117 - 119°)
Explanation: lone pair
repels more than bonding pair

Question 28

bond angle in XeF4

Answer 28

90°

Question 29

why the lone pairs of electrons are opposite each other in this molecule (XeF4)

Answer 29

lone pairs (or they) repel more than bonding pairs (or most) (1) (so are) as far apart as possible

Question 30

Name the shape of this molecule, given that the shape describes the positions of the Xe and F atoms only (XeF4)

Answer 30

square planar