Bonding

Question 1

Define ionic bonding

Answer 1

Electrostatic forces of attraction between oppositely charged ions formed by electron transfer

Question 2

What is the structure of sodium chloride?

Answer 2

Giant ionic lattice

Question 3

Why do ionic substances have high mp/bp?

Answer 3

Strong electrostatic forces of attraction between oppositely charged ions require high energy to break

Question 4

Why is the ionic radii of positive ions smaller?

Answer 4

One less shell of e- so force of nucleus holds them closer

Question 5

Why is the radii of negative electrons bigger?

Answer 5

More e- but same number of protons, so pull of nucleus is shared over more e-, reducing attraction per e-

Question 6

What is covalent bonding?

Answer 6

Shared pair of e-

Question 7

What is dative covalent bonding?

Answer 7

When a shared pair of e- in the covalent bond comes from one of the bonding atoms

Question 8

What can dative covalent bonding also be called?

Answer 8

Co-ordinate bonding

Question 9

Give examples of molecules with dative covalent bonding

Answer 9

NH4+
H3O+
NH3BF3

Question 10

How do you draw a dative covalent bond?

Answer 10

Arrow goes from the atom donating the e- pair to the one that is deficient

If there’s a charge, then add square brackets around it and write the charge outside

Question 11

What is metallic bonding?

Answer 11

Electrostatic forces of attraction between positive metal ion and delocalised e-

Question 12

Describe 3 factors affecting the strength of metallic bonding

Answer 12

1) Number of protons / strength of nuclear attraction
- More protons –> stronger bond

2) Number of delocalised e- per atom
- ore delocalised e- –> stronger bond

3) Size of ion
- Smaller ion –> stronger bond

Question 13

What is a simple molecular structure?

Answer 13

With intermolecular forces between molecules
Eg. Van der Waals / permanent dipoles / hydrogen bonds

Question 14

Give examples of molecules with a simple molecular structure

Answer 14

CO2
H2O
H4

Question 15

What is a macromolecular structure?

Answer 15

Giant molecular structures

Question 16

Give examples of molecules with a macromolecular structure

Answer 16

Diamond
Graphite
Silicon dioxide
Silicon

Question 17

Describe the difference between the mp / bp of simple molecular vs macromolecular structures

Answer 17

Simple –> low mp sue to weak intermolecular forces between molecules (must specify type if force in answers)

Macro –> high mp due to many strong covalent bonds which take a lot of energy to break

Question 18

Conductivity of ionic compound when solid VS when molten

Answer 18

Solid –> poor as ions can’t move / fixed in lattice

Molten –> good as ions are free to move

Question 19

Conductivity of simple molecular substances when solid VS molten

Answer 19

Solid –> poor as no ions to conduct / e- are localised

Molten –> poor as no ions

Question 20

Why can graphite conduct electricity when solid but not diamond?

Answer 20

Graphite –> free delocalised e- between layers as each carbon atom is only bonded to 3 other carbon atoms

Diamond –> e- can’t move

Question 21

Conductivity of metallics structures when solid VS molten

Answer 21

Both –> good as there are delocalised e-

Question 22

How would you explain the shape of a molecule?

Answer 22

1) state number of bonding pairs & lone pairs of e-

2) State that e- pairs repel to get as far away as possible

3) If no lone pairs –> state that e- pairs repel equally

4) If lone pairs –> state that lone pairs repel more than bonding pairs of e-

5) State shape and bond angle

Question 23

How many degrees does each lone pair reduce the bond angles by?

Answer 23

2.5

Question 24

What is electronegativity?

Answer 24

Relative tendency of an atom in a covalent bond in a molecule to attract electron pairs to itself

Question 25

Which atoms are most electronegative

Answer 25

Fluorine Oxygen Nitrogen Chlorine

Question 26

How is electronegativity measure?

Answer 26

Pauling scale (0-4)

Question 27

Explain the trend in electronegativity cross a period

Answer 27

Increase --> number of protons increase and atomic radius decreases as e- in same shell are pulled in more

Question 28

Explain the trend in electronegativity down a group

Answer 28

Decrease --> distance between nucleus and outer e- increases and shielding of inner shell e- increases

Question 29

How do you know if a compound is purely covalent?

Answer 29

Small difference in electronegativity

Question 30

What does it tell you if a compound contains elements with large electronegativity difference?

Answer 30

It's ionic

Question 31

How do permanent dipoles arise (aka polar covalent bond)?

Answer 31

When bonds have different electronegativities of around 0.3-1.7 Unequal distribution of e- produces charge separation (dipole)

Question 32

Are symmetric molecules polar or non-polar? Why?

Answer 32

Non-polar as all bonds are identical and no lone pairs Dipoles cancel out

Question 33

Is CH3Cl polar or non-polar?

Answer 33

Polar

Question 34

Where do Van der Waals forces occur?

Answer 34

Between all molecular substances and noble gases (not ionic substances)

Question 35

How are induced dipole-dipole interactions formed?

Answer 35

1) In molecules, electrons are moving constantly and randomly 2) Causing electron density to fluctuate and parts of the molecule become more / less negative (temporary / transient dipoles) 3) These instantaneous dipoles cause dipoles to form in neighbouring molecules (induced dipoles) Induced dipole is always opposite to the original

Question 36

What is the main factor affecting the size of Van der Waals

Answer 36

More e- in a molecule = higher chance of dipole forming --> make vdW stronger between molecules --> greater boiling points

Question 37

Why does be increase down group 7?

Answer 37

More e- in bigger molecules --> cause increase in size of vdW between molecules

Question 38

Why does boiling point oof alkane homologous series increase?

Answer 38

More e- in bigger molecules --> increased size of vdW between molecules

Question 39

How does the shape of a molecule affect the size of vdW?

Answer 39

Longer chain alkanes have larger surface area of contact between molecules for vdW (compared to spherical / branched) --> stronger vdW

Question 40

What type of molecules do dipole-dipole forces occur between?

Answer 40

Polar

Question 41

Where do hydrogen bonds occur?

Answer 41

Between hydrogen atom on one molecule and N / O / F on another molecule

Question 42

Order the intermolecular forces in terms of bp from highest to lowest

Answer 42

Hydrogen Permanent dipole-dipole Van der Waals

Question 43

What must you always show hen drawing hydrogen bonding between 2 molecules?

Answer 43

Lone pairs on O / N / F And charges of H & O / N / F