1b)ii) - Structure and bonding

Question 1

What are intermolecular forces acting between molecules also known as

Answer 1

Inter molecular forces acting between molecules are also known as Van der waals forces

Question 2

What are the several types of intermolecular forces (Van der waals)

Answer 2

• London dispersion forces
• permanent dipole - permanent dipole interactions
• hydrogen bonding

Question 3

What are London dispersion forces

Answer 3

London dispersion forces are forces of attraction that can operate between all atoms and molecules.

Question 4

What is the strength of LDFS

Answer 4

London dispersion forces are much weaker than all types of bonding

Question 5

What are London dispersion forces the result of

Answer 5

They are formed as a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules

Question 6

What is the strength of London dispersion forces related to

Answer 6

The strength of London dispersion forces is related to the number of electrons within an atom of molecule

Question 7

What is the link between side of molecule and strength of LDFS

Answer 7

The bigger the molecule the stronger the London dispersion forces

Question 8

More electrons means what in terms of London dispersion force

Answer 8

More electrons means stronger London dispersion force

Question 9

What causes a temporary dipole

Answer 9

The electrons in an atom may become unevenly distributed causing a temporary dipole

Question 10

When does the strength of LDFs increase

Answer 10

The strength of London dispersion force increases as the size of the atoms increases

Question 11

When are London dispersion forces important

Answer 11

London dispersion forces are important in the absence of other types of attractions between molecules

Question 12

When is a molecule described as polar

Answer 12

A molecule is described as polar if it has a permanent dipole

Question 13

What is the strength of permanent dipole - permanent dipole interactions

Answer 13

Permanent dipole - permanent dipole interactions are stronger than London dispersion forces for molecules with similar numbers of electrons

Question 14

Which bonds where a hydrogen atom bonds with an atom of strong electronegativity are highly polar

Answer 14

Bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen are highly polar

Question 15

What is a hydrogen bond

Answer 15

Bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen are highly polar

Question 16

What is the strength of a hydrogen bond

Answer 16

A hydrogen bond is stronger than other forms of intermolecular forces but weaker than a covalent bond

Question 17

What are H - O bonds

Answer 17

The H - O bonds are polar covalent

Question 18

Why is water a polar molecule

Answer 18

The whole water molecule is polar because it has a ‘positive end’ and a ‘negative end’

Question 19

When do we say the molecule has a permanent dipole

Answer 19

We say the molecule has a permanent dipole if the S+ve centre and S-ve centre do not coincide

Question 20

What do molecules with a permanent dipole attract

Answer 20

Molecules with a permanent dipole attract each other. The attraction is stronger than London dispersion forces

Question 21

What is hydrogen binding an example of and what do they still include

Answer 21

Hydrogen bonding is a particular example of permanent dipole - permanent dipole attraction. Chemicals which have hydrogen bonding still have London dispersion forces as well

Question 22

What are the melting and boiling points of polar substances compared to non polar substance with similar numbers of electrons

Answer 22

The melting and boiling points of polar substances are higher than the melting and boiling points of non polar substances with similar numbers of electrons

Question 23

What are properties of substances that are affected by hydrogen bonding

Answer 23

Boiling points, melting points, viscosity and solubility /miscibility in water are properties of substances that are affected by hydrogen bonding

Question 24

What happens when a molecule contains polar bonds but is symmetrical

Answer 24

When a molecule contains polar bonds but is symmetrical i.e tetrahedral or linear. The polarities cancel each other out and the molecule is non polar

Question 25

What are ionic compounds and polar molecular compounds soluble and insoluble in

Answer 25

Ionic compounds and polar molecular compounds tend to be soluble in polar solvents such as water and insoluble in non-polar solvents (like dissolve like)

Question 26

What are non polar molecular substances soluble and insoluble in

Answer 26

Non polar molecular substances tend to be soluble in non polar solvents and insoluble in polar solvents

Question 27

What are key features you need to consider to predict the solubility of a compound

Answer 27

• presence in molecules of O - H or N - H bonds, which could result in a molecule possessing a permanent dipole
• water is a useful solvent for ionic compounds because it is polar
• the larger the molecule the stronger the intermolecular forces and therefore the higher the viscosity of the liquid (thicker the liquid)

Question 28

What happens in a temporary dipole

Answer 28

I.e one side of the atom becomes fleetingly negative while the other side becomes positive. Which has a knock on effect on the neighbouring atoms

Question 29

What are London dispersion forces caused by

Answer 29

They are caused by uneven distribution of electrons

Question 30

Which type of ends do dipole-dipole attractions arise in

Answer 30

Dipole -dipole attractions arise between oppositely charged ends of DIFFERENT MOLECULES

Question 31

What is important to remember about permanent - dipole to permanent - dipole attractions

Answer 31

THEY ARISE BETWEEN DIFFERENT MOLECULES !!!!!!

Question 32

What will happen if you have a molecule which contains dipole dipole as well as LDFs

Answer 32

If you have an atom with LDFs and pd-pd melting and boiling point will be higher

Question 33

Which type of molecules do intermolecular bonding happen between

Answer 33

Intermolecular bonding happen between DIFFERENT MOLECULES !!!!!!!!!!!!!!!

Question 34

Which atoms are hydrogen bonds formed with

Answer 34

• fluorine
• oxygen
• nitrogen

Question 35

What will happen to the mp/bp of a compound when hydrogen bonding is present

Answer 35

When H- bonding is present the compound will have a much higher melting and boiling point when compared to similar molecules

Question 36

What is the mass number

Answer 36

The number of protons + neutrons

Question 37

What is the atomic number

Answer 37

The number of protons

Question 38

Which is stronger bonds between molecules or ions?

Answer 38

Bonds between molecules are weaker than bonds between ions

Question 39

What does lower viscosity mean

Answer 39

Stronger Van der waals forces

Question 40

What some elements have higher boiling points than others

Answer 40

• there are stronger / more Van der waals forces
• there are more electrons
• correctly identify what Van der waals forces they have

Question 41

What are the anomalous boiling points of ammonia water and hydrogen fluoride a result of

Answer 41

The anomalous boiling points of ammonia, water and hydrogen fluoride are the result of hydrogen bonding