Shapes of Molecules

Question 1

How are molecules formed?

Answer 1

Atoms joined by covalent bond

Question 2

What determines the shape of a molecule?

Answer 2

Arrangement in space of the atoms

Question 3

What is the Electron Pair Repulsion Theory

Answer 3

It explains shapes of simple molecules with atoms bonded to a central atom. According to this theory,

• electron pairs in the valence shell of the central atoms repel eachother as far apart as geometrically possible
• lone pairs have a greater repelling effect than bonding pairs

Question 4

If the central atom is in group 2, what shape will the molecule be and what will be the bond angle?

Answer 4

Linear, 180 degrees

Question 5

If the central atom is in group 3, what shape will the molecule be and what will be the bond angle?

Answer 5

Trigonal planar, 120 degrees

Question 6

If the central atom is in group 4, what shape will the molecule be and what will be the bond angle?

Answer 6

Tetrahedral, 109.5 degrees

Question 7

If the central atom is in group 5, what shape will the molecule be and what will be the bond angle?

Answer 7

Pyramidal, 107 degrees

Question 8

If the central atom is in group 6, what shape will the molecule be and what will be the bond angle?

Answer 8

V-shaped, 104.5 degrees

Question 9

Which has the greatest repulsion between bonding pairs?

Answer 9

Lone pair : Lone Pair
Lone pair : Bond pair
Bond pair : Bond pair

Question 10

Why when the central tom is in group 5, is the bond angle 107 degrees?

Answer 10

It has four bond pairs which gives it the tetrahedral arrangement, but due to the strong repulsion of the lone pairs, they bond pairs are pushed close together creating a bond angle of 107 degrees

Question 11

How can a molecule have polar bonds but be a non-polar molecule?

Answer 11

Occurs when a molecule has a high degree of symmetry and geometric centre

Question 12

If a molecule has a high degree of symmetry, what does this mean?

Answer 12

The molecule is non polar

Question 13

What are the symmetrical molecules?

Answer 13

Linear, Trigonal, Tetrahedral

Question 14

Which atom is partially negative?

Answer 14

Greater electronegativity

Question 15

Which atom is partially positive?

Answer 15

Lesser electronegativity

Question 16

How is a molecule symmetrical?

Answer 16

Example, Centre of negative charge in the central atom coincides with the geometric centre of positive charge, caused by the surrounding atoms.

Question 17

How is a molecule not symmetrical?

Answer 17

Centres of positive and negative charge do not coincide. Negative charge of central atom is at the apex and the centre of positive charge is seperated

Question 18

What is intramolecular bonding?

Answer 18

Bonding within the molecule that holds the atom together

Question 19

What is intermolecular bonding?

Answer 19

Forces/bonding between molecules

Question 20

What is hydrogen bonding?

Answer 20

a special type of dipole-dipole interaction, which occurs when hydrogen is bonded to small, highly electronegative atoms such as O, N or F

Question 21

Hydrogen bonding in water

Answer 21

Highly polar due to electronegativity difference

Partial negative has strong attraction for partial positive

Question 22

What do strong intermolecular forces mean?

Answer 22

It means high boiling point

Question 23

Hydrogen sulfide has a electronegativity difference of 0.4, what does this mean

Answer 23

It means it is weakly polar. The partial negative charge is more diffuse and less effective on large sulphur atom than on oxygen atom

Question 24

How does the boiling point usually increase?

Answer 24

It increases as the relative molecular mass increases

Question 25

What occurs in hydrogen bonding?

Answer 25

Hydrogen bonds to a small, highly electronegative atom which means the share of electrons is going to be small. It readily attracts too another electronegative atom

Question 26

Since the hydrogen atom is small, what does this mean?

Answer 26

Two atoms can bond to it, hydrogen bond and other by covalent bond

Question 27

What is dipole-dipole interactions?

Answer 27

Negative end of one dipole is attracted to the positive end of another

Question 28

Why are dipoles permanent?

Answer 28

Due to their polarity