Attractions & Repulsions

Question 1

What 3 assumptions are made for the ideal gas equation?

Answer 1

• Molecules of the gas have zero volume
• There are no interactions between gas molecules
• All collisions are elastic (i.e have no energy loss)

Question 2

What is the ideal gas equation, and what does each symbol represent?

Answer 2

pV = nRT
p = pressure (Pa)
V = volume (m^3)
n = no. moles
R = ideal gas constant (J K-1 mol-1)
T = temperature (K)

Question 3

What determines the pressure of a gas?

Answer 3

• The frequency of molecules hitting the wall of the container
• The force the molecule exert on the wall when they hit (dependent on how fast they are moving)

Question 4

Which combination of electronegativities tends to form covalent bonds?

Answer 4

Two highly electronegative atoms tend to form covalent bonds

Question 4

Which combination of electronegativities tends to form covalent bonds?

Answer 4

Two highly electronegative atoms tend to form covalent bonds

Question 5

Which combination of electronegativities tends to form ionic bonds?

Answer 5

One highly electronegative and one low electronegative atom tend to form ionic bonds

Question 6

Which combination of electronegativities tends to form metallic bonds?

Answer 6

Two low electronegativity atoms tend to form metallic bonds

Question 7

What are dipole moments?

Answer 7

Dipole moments are vectors that tell us the overall distribution of charge in the polar molecule

Question 8

What are permanent dipoles?

Answer 8

Diatomic molecules containing two atoms with significantly differing electronegativities are said to have a permanent dipole (i.e. a permanent drawing of charge to one atom in the molecule)

Question 9

Through what two methods can we measure if a molecule has a dipole moment?

Answer 9

• Microwave spectroscopy
• Measuring its dielectric constant

Question 10

What is the difference in electronegativity for non-polar bonds?

Answer 10

Less than ~0.5

Question 11

What is the difference in electronegativity for ionic bonds?

Answer 11

Greater than ~2

Question 12

What is the difference in electronegativity for polar bonds?

Answer 12

Between ~0.5 and ~2

Question 13

The greater the difference in electronegativity, the greater the…

Answer 13

Ionic character

Question 14

What are two methods of measuring whether a molecule has a dipole moment?

Answer 14

Microwave spectroscopy
Measure it dielectric constant

Question 15

How can we use microwave spectroscopy to find whether a molecule has a dipole moment?

Answer 15

In the gas phase, if the molecule has a dipole moment it will display a spectra

Question 16

What is dielectric constant, and how does this tell us whether a molecule has a dipole moment?

Answer 16

Dielectric constant shows the ability of polar molecules to align in an electric field; if the molecule has a dipole moment, it will align

Question 17

What is the equation for calculating the potential energy of dipole forces?

Answer 17

(Dipole moment 1 x Dipole moment 2) / Distance apart^3

Question 18

Are there more intermolecular forces in liquids than solids?

Answer 18

No. There are more intermolecular forces in the solid state than liquid or gas

Question 19

What is hydrogen bonding?

Answer 19

An extreme example of dipole-dipole interactions, between H and usually F, O or N

Question 20

How many H-bonds form per water molecule?

Answer 20

4

Question 21

Why do ionic compounds dissolve in water?

Answer 21

Water is able to break strong ionic bonds by forming ion-dipole bonds

Question 22

What is polarisability of an atom?

Answer 22

The tendency of the electron field of an atom to become distorted when subjected to an electrical force

Question 23

What is the relationship between polarisability and electronegativity?

Answer 23

There is an inverse relationship between polarisability and electronegative.
Highly electronegative elements are not easily polarised

Question 24

What two factors increase polarisability?

Answer 24

- Larger molecular size - More electrons

Question 25

Name all the intermolecular forces in order of decreasing strength

Answer 25

STRONGEST Ion-dipole Dipole-dipole H-bonding Dipole-induced dipole London forces WEAKEST

Question 26

What factors are responsible for dipole-induced dipole interactions?

Answer 26

The dipole moment of the polar molecule and the polarisability of the nonpolar molecule

Question 27

What are London dispersion forces?

Answer 27

Induced dipole-induced dipole interactions

Question 28

What feature of electron distribution allow London forces to form?

Answer 28

At any instant, the distribution of electrons are an atom will not be even, forming transient delta positive and delta negative dipoles

Question 29

How do London forces form?

Answer 29

- Transient fluctuations in electron density - Transient dipoles - Transient induced dipoles in adjacent molecules - Attraction between these dipoles are London forces

Question 30

How does the size of the atom affect the strength of London forces?

Answer 30

The larger the atom, the more polarisable it becomes, so the stronger the London forces

Question 31

How does the compactness of the molecule affect the strength of London forces?

Answer 31

The more compact the molecule, the weaker the London forces

Question 32

What are the 4 types of crystalline solids?

Answer 32

- Molecular structures (e.g. CO2) - Covalent network structures (e.g. Diamond) - Metals (e.g. Fe) - Ionic compounds (e.g. NaCl)

Question 33

What is the electrical conductivity and melting/boiling point of molecular structures?

Answer 33

Electrical conductivity = low Melting/boiling point = low

Question 34

What is the solubility of molecular structures?

Answer 34

Some dissolve in water, many dissolve in organic solvents

Question 35

What is the electrical conductivity and melting/boiling point of covalent network structures?

Answer 35

Electrical conductivity = generally low Melting/boiling point = very high

Question 36

What is the solubility of covalent network structures?

Answer 36

Generally insoluble in water and organic solvents

Question 37

What is the electrical conductivity and melting/boiling point of metals?

Answer 37

Electrical conductivity = good Melting/boiling point = generally high

Question 38

What is the solubility of metals?

Answer 38

Insoluble

Question 39

What is the electrical conductivity and melting/boiling point of ionic compounds?

Answer 39

Electrical conductivity = high when molten or in aqueous solution Melting/boiling point = high

Question 40

What is the solubility of ionic compounds?

Answer 40

Some soluble in water, but insoluble in organic solvents

Question 41

Why does evaporation occur at lower temperatures, rather than boiling?

Answer 41

At lower temperatures, the vapour pressure of the liquid is lower than the atmospheric pressure, meaning bubbles cannot form

Question 42

Why does boiling occur at higher temperatures?

Answer 42

At the boiling point, the vapour pressure of the liquid is equal to the atmospheric pressure, meaning bubbles can form and rise, and boiling occurs

Question 43

What is equilibrium vapour pressure?

Answer 43

A measure of the tendency of molecules to escape from the liquid phase and enter the vapour phase (evaporate)

Question 44

What is equilibrium vapour pressure dependent on?

Answer 44

- Temperature - Intermolecular forces

Question 45

What is the relationship between intermolecular forces and equilibrium pressure?

Answer 45

The weaker the intermolecular interactions, the higher the equilibrium vapour pressure

Question 46

What is the conversion of solid directly to vapour known as?

Answer 46

Sublimation

Question 47

What is the conversion of vapour directly to solid known as?

Answer 47

Deposition

Question 48

What is the triple point?

Answer 48

The specific temperature and pressure on a phase diagram at which all three phases co-exist in equilibrium

Question 49

What phases are present at pressures below the triple point?

Answer 49

At pressure below the triple point, we do not see liquids, just solids and gases

Question 50

What is the critical point?

Answer 50

The point at which if you increase the temperature and/or pressure any further, you will get "supercritical fluid"

Question 51

What is "supercritical fluid"?

Answer 51

The state at which the lines between liquid and gas become blurred; the density of the substance is close to that of a liquid, but the viscosity is like that of a gas