Chapter 6 - Shapes Of Molecules And Intermolecular Forces

Question 1

What is the electron-pair repulsion theory?

Answer 1

• electrons repel one another
• electron pairs surrounding a central atom determines the shape of the molecule/ion
• electron pair repel to be as fair apart as possible
• arrangement of electron pair minimises repulsion holding the bond in a specific shape
• different number of electron = different shape

Question 2

What are three-dimensional shape s used to represent molecules 3D shape?

Answer 2

• a straight line = bond IN plane of the page
• a triangle filled = bond is coming OUT the page
• a triangle made out of multiple lines = bong going INTO the page

Question 3

The shape of molecules depend on …………………………………….

Answer 3

Number of pairs of electrons

Question 4

What must be included for a molecule to have a LINEAR shape?

Answer 4

• 2 electron pairs

* 180° between each bond

Question 5

What must be included for a molecule to have a TRIGONAL PLANAR shape?

Answer 5

• 3 electron pairs

* 120° angles between each bond

Question 6

What must be included for a molecule to have a TETRAHEDRAL shape?

Answer 6

• 4 electron pairs
• 109.5° between each bond
• 0 lone-pairs

Question 7

What must be included for a molecule to have a OCTOHEDRAL shape?

Answer 7

• 6 electron pairs

* 90° between each bond

Question 8

How do lone pairs effect the shape of a molecule?

Answer 8

• it is closer to the central atom and occupies more space
• higher repulsion decreases the bond angle
• bond angle reduce by 2.5° for each lone pair bench changing the shape of the molecule

Question 9

What must be included for a molecule to have a pyramidal shape?

Answer 9

• 3 bond pairs
• 1 lone-pair
• 107 ° between bonds

Question 10

What must be included for a molecule to have a non-linear shape?

Answer 10

• 2 bond pairs
• 2 lone-pairs
• 104.5° between each bond

Question 11

What’s electronegativity?

Answer 11

The attraction of a bonded atom for the pair of electrons in a covalent bond

Question 12

How is electronegativity measured?

Answer 12

Depends on the position of the periodic table

Increases across and increase up the periodic table

Question 13

Complete the graph
Bond type Electronegativity difference

Covalent a)

Polar covalent b)

Ionic C)

Answer 13

a) 0
b) 0 to 1.8
c) greater than 1.8

Question 14

Complete the sentence:
•if electronegativity are the same the ……………………….
•if the electronegativity are vastly different …………………… occurs
•if the electronegativity are slightly different ………………………. exists
•different electronegativity causes a ………………

Answer 14

• molecules is non-polar
• ionic bonding
• a polar molecule
• permeant dipole

Question 15

What is a non-polar bond?

Answer 15

The bonded electron pair is shared equally between the bonded atoms

Question 16

What molecules of elements have a pure covalent bond?

Answer 16

Hydrogen, oxygen and chlorine etc

Question 17

What’s a polar covalent bond?

Answer 17

The bonded electron pair is shared unequally and have different electronegativity values

Question 18

What’s a dipole?

Answer 18

Separation of opposite charges

Question 19

Why are water molecules polar?

Answer 19

Each O-H bond has induced dipole which act in different directions and do not oppose directly

Question 20

Why is carbon non-polar?

Answer 20

The double bond between C and O has a permanent dipole which act in different directly and exactly oppose. Hence, cancels out the dipole making the dipole 0

Question 21

Complete the sentence:

Ionic solutes dissolve in ……

Answer 21

• polar solvents

Question 22

What properties do covalent bonds have?

Answer 22

• intermolecular forces

* very strong

Question 23

What are the three types do intermolecular forces? And in order of strength from lowest to highest

Answer 23

• induced dipole-dipole interaction ( known as London Forces)
• permeant dipole-dipole interactions
• hydrogen bonds

Question 24

Outline the intermolecular force known as LONDON FORCES

Answer 24

• weakest intermolecular forces
• exists in all molecules
• at the beginning, there is an even distribution, the movement of electrons forming a dipole known as instantaneous dipole
• it is constantly changing
• the instantaneous dipole induces a dipole in another
• only temporary

Question 25

What happens to the London Forces when there are more electrons?

Answer 25

• larger the instantaneous/induced poles
• greater the London force
• stronger attractive force between the molecules
• more energy needed to overcome the intermolecular force, increasing the boiling point

Question 26

Outline the intermolecular force known as PERMEANT DIPOLE-DIPOLE INTERACTION

Answer 26

• acts between the permanent dipoles in different polar molecules
• high amount of energy need to break the intermolecular forces

Question 27

What is a simple molecular substance?

Answer 27

Made of simple molecules

Question 28

What is a simple molecular lattice?

Answer 28

Simple molecules form a regular structure.
•molecules held by weak intermolecular forces
•molecules bonded together strongly by covalent bonds

Question 29

List the properties if simple molecular substances

Answer 29

• low melting/boiling point - weak intermolecular forces can be broken easily.
• during melting point - weak intermolecular break but covalent bonds are strong so they don’t break
• solubility - non-polar substance aren’t soluble in polar solvents. This is because it would involve breaking stronger attractions between the molecules of the polar substance. But in a non-polar solvents, they are soluble as they can form weak attraction between the solvent and solute

Question 30

Outline the intermolecular force known as HYDROGEN BONDING

Answer 30

Occurs between molecules which contain an electronegative atom with a lone pair of electrons and a hydrogen atom attached to an electronegative atom.

Question 31

How is an hydrogen shown by?

Answer 31

Dashed line between lone pair and hydrogen atom

Question 32

Are hydrogen bonds stronger than London Forces?

Answer 32

Yes

Question 33

What are the anomalous properties of water?

Answer 33

• the solid (ice) is less dense than the liquid (water) - hydrogen bonds hold water molecules apart in open lattice structure but in ice they are held even further
• high surface tension and viscosity
• high melting/boiling point