Week 6

Question 1

In polyatomic molecules, the centre atom…

Answer 1

is the one that needs to share the greatest number of electrons

Question 2

Resonance structures

Answer 2

Sometimes the Lewis model allows several valid structures
* e.g. O3

Question 3

double headed arrow

Answer 3

used for resonance

Question 4

Formal charge =

Answer 4

Valence electrons of free atom - Lone pairs of electron - 1/2(Shared electrons)

Question 5

Octet rule

Answer 5

Atoms can have a maximum of 4 electron pairs (8 e-) surrounding them (H can only have 1 electron pair, 2 e-)

Question 6

Lewis structures

Answer 6

• Full bonds are represented by solid lines.
• Partial bond can be represented by dashed lines.
• Lone pairs are represented by dots.

Question 7

VSEPR theory allows us to find

Answer 7

→ 3D arrangement of electron groups
→ 3D arrangement of atoms (ie. when lone pairs are ignored)
= the SHAPE of the molecule

Question 8

3D arrangement for 2 electron groups

Answer 8

Linear
* 180°

Question 9

3D arrangement for 3 electron groups

Answer 9

Trigonal
* 120°

Question 10

3D arrangement for 4 electron groups

Answer 10

Tetrahedral
* 109.5°

Question 11

3D arrangement for 5 electron groups

Answer 11

Trigonal Bipyramidal
* Angle between E and A 90°
* Angle between E and E 120°

Question 12

3D arrangement for 6 electron groups

Answer 12

Octahedral
* 90°

Question 13

The shapes of molecules with four electron groups (tetrahedral arrangement) may be:

Answer 13

1. Tetrahedral (4 bonds, no lone pairs)
2. Trigonal pyramidal (3 bonds, 1 lone pair)
3. Bent

Question 14

T-shaped

Answer 14

This molecule is planar but has bond angles a little below 90°. The atoms are “squeezed together” by the “lone pairs”
* e.g. CIF3

Question 15

If the two atoms forming a bond have different electronegativities, the electrons will be more strongly attracted to the ____ atom

Answer 15

more electronegative

Question 16

In polyatomic molecules, the bond dipoles add together to determine

Answer 16

the overall polarity of the molecule

Question 17

If the molecule is symmetric, the bond dipoles will…

Answer 17

cancel out and the molecular dipole will be 0

Question 18

In asymmetric molecules, the bond dipoles will…

Answer 18

NOT completely cancel out and the molecule will have a finite dipole

Question 19

C can bond to…

Answer 19

• itself
• metals
• heteroatoms

Question 20

C-C and C-H bonds

Answer 20

are strong and unreactive
⇒ provides solid scaffolds

Question 21

If a covalent bond is formed between two atoms with limited differences in electronegativity

Answer 21

Then that bond is said to be “non-polar”.
In asymmetric polyatomic molecules with polar bonds the overall dipole “will not cancel out”

Question 22

If a covalent bond is formed between two atoms with large differences in electronegativity

Answer 22

Then that bond is said to be “polar”.
In symmetric polyatomic molecules the net molecular dipole will be “zero”

Question 23

An easy way to figure out what hybridization an atom has

Answer 23

Count the number of atoms bonded to it and the number of lone pairs.
* Double and triple bonds still count as being only bonded to one atom.

Question 24

More nodes

Answer 24

⇒ shorter wavelength, more momentum and more energy

Question 25

presence of OH groups will lead to…

Answer 25

H-bonding interactions

Question 26

delocalised pi electron density will lead to…

Answer 26

dispersion interactions

Question 27

a charged group with N-H bonds will lead to…

Answer 27

interactions with ion and polar groups