Module 2 - chapters 5 and 6

Question 1

Give a general overview about ionic bonding

Answer 1

• Between metals and non-metals
• Ions have opposite charges and so are attractive
• OILRIG
• Ions exchange electrons to achieve a full outer shell and a stable electron configuration
• the ions form a giant ionic lattice which has high melting and boiling points due to strong intramolecular forces and electrostatic forces
• The ions are conductive if molten or aqueous because the ions are free to move
• the ions can be separated using electrolysis

Question 2

What is a key feature of strong ionic bonding?

Answer 2

A large difference in charge/a larger charge.

E.g. Al³⁺ and O²⁻ has a larger difference in charge than Na⁺ and Cl⁻ so aluminium oxide is stronger than sodium chloride.

Question 3

Why are ionic substances typically brittle?

Answer 3

As you try to move the ions, the ions of the same charge are brought side-by-side and so the crystal repels itself apart

Question 4

What does giant mean in terms of a giant ionic structure?

Answer 4

When you can’t state how many ions there actually are in the structure

Question 5

What does it mean if an ion is 6:6 co-ordinated?

Answer 5

The ion is the centre is being touched by 6 other ions and those ions touched by 6 other ions to form a giant structure.

For example: a sodium ion in the centre of a giant ionic lattice is being touched by 6 chloride ions and each chloride ion by 6 sodium ions.

Question 6

Do all ionic substances have high or low melting and boiling points?

Answer 6

High

Question 7

How do the sizes of ions effect the attractions of ions?

Answer 7

If the ions are smaller they get closer together and so the electrostatic attractions are greater. This is because the charge isn’t spread over a large density.

Question 8

What defines how soluble an ionic substance is?

Answer 8

• the nature of the ionic lattice that needs breaking down
• the attraction of the water molecules (or other polar solvents) to the ions
• ionic lattice strength dominates, solubility decreases with increasing ionic charge

Question 9

What is said when an ion has a full outer shell?

Answer 9

It is isoelectronic to a noble gas

Question 10

What is a hydrogen ion also known as?

Answer 10

A proton

Question 11

Why do covalently bonded atoms stay together?

Answer 11

The positive nuclei are attracted to the shared negative electrons in between the nuclei, this forms strong intramolecular forces which hold atoms together

Question 12

What prevents the positive nuclei repelling between covalently bonded atoms?

Answer 12

High electron density between nuclei balances the repulsion of the nuclei

Question 13

How is the degree of strength a covalent bond has measured?

Answer 13

As average bond enthalpy, the higher this value the stronger the covalent bond

Question 14

What is a daitive bond also known as?

Answer 14

A co-ordinate bond

Question 15

What is a daitive bond?

Answer 15

A covalent bond in which both electrons come from the same atom.

Question 16

How do you show the daitive bond in a displayed formula?

Answer 16

Draw an arrow rather than just a line to represent the bond. The arrow should point to the atom (previously an ion) which didn’t bring any electrons to the bond.

Question 17

How can you tell the difference between a regular covalent bond and a daitive covalent bond?

Answer 17

It is impossible to tell the difference once the bond is formed, there is no difference in reality.

Question 18

Why do ions remain together after exchanging electrons?

Answer 18

The ions are held together by strong electrostatic attractions between the negative charges.

Question 19

What are some properties of giant ionic lattices?

Answer 19

• High melting point and boiling point
• Brittle
• Conductivity

Question 20

Is the cathode positively or negatively charged?

Answer 20

negatively (attracts positive cations)

Question 21

Is the anode positively or negatively charged?

Answer 21

positively (attracts negative anions)

Question 22

What is formed when ammonia and hydrogen chloride are reacted? What do the reactants look like and what does the product look like?

Answer 22

Ammonium chloride,

reactants = colourless gases, product = a thick white smoke

Question 23

what is the definition for a covalent bond?

Answer 23

when two non-metals share a pair of electrons to form structures isoelectronic to noble gases.

Question 24

Is hydrochloric acid ionically or covalently bonded?

Answer 24

Covalently

Question 25

How do you show a daitive bond in a displayed formula?

Answer 25

Draw an arrow pointing to the atom which didn't bring anything to the molecule

Question 26

How are ammonium ions formed?

Answer 26

by the transfer of a hydrogen ion from the hydrogen chloride (when ammonia and HCl are reacted) to the lone pair of electrons on the ammonia molecule

Question 27

What do acids form with water?

Answer 27

Hydroxonium ions (H₃O⁺)

Question 28

How is boron trifluoride different from other molecules?

Answer 28

it is electron deficient, the boron only has 3 pairs of electrons in its bonding level whereas there would be room for 4 pairs.

Question 29

What is the valence shell electron pair repulsion theory (VSEPR)?

Answer 29

that bonded electron pairs repel bonded electron pairs, but lone pairs repel more. This is to reduce electrostatic attraction. "Molecules take up the shape that minimises the repulsion between electron pairs within the molecule."

Question 30

Is Beryllium chloride electron deficient?

Answer 30

yes

Question 31

How would you draw a double bond in a 3D displayed formula?

Answer 31

A double bond only counts as one bond/one area of electron density so you draw it as a singular bond

Question 32

What are lone pairs also known as?

Answer 32

non-bonded pairs

Question 33

why do lone pairs have a more concentrated negative charge?

Answer 33

because they are not shared between two atoms

Question 34

What is the name of the structure of a molecule with 2 bonded electron pairs?

Answer 34

linear

Question 35

What is the bond angle in a linear molecule?

Answer 35

180°

Question 36

What is the name of the structure of a molecule with 2 bonded electron pairs and 2 lone pairs?

Answer 36

non-linear

Question 37

What is the bond angle in a non-linear molecule?

Answer 37

104.5°

Question 38

What is the name of the structure of a molecule with 3 bonded electron pairs?

Answer 38

trigonal planar

Question 39

What is the bond angle in a trigonal planar molecule?

Answer 39

120°

Question 40

What is the name of the structure of a molecule with 3 bonded electron pairs and 1 lone pair?

Answer 40

trigonal pyramidal

Question 41

What is the bond angle in a trigonal pyramidal molecule?

Answer 41

107°

Question 42

What is the name of the structure of a molecule with 4 bonded electron pairs?

Answer 42

tetrahedral

Question 43

What is the bond angle in a tetrahedral molecule?

Answer 43

109.5°

Question 44

What is the name of the structure of a molecule with 5 bonded electron pairs?

Answer 44

trigonal bipyramidal

Question 45

what is the bond angle in a trigonal bipyramidal molecule?

Answer 45

120° between the base and 90° between the vertical

Question 46

what is the name of the structure of a molecule with 6 bonded electron pairs?

Answer 46

octahedral

Question 47

what is the bond angle in an octahedral molecule?

Answer 47

90°

Question 48

What is electronegativity?

Answer 48

The ability of an atom in a covalent bond to attract the bonded pair of electrons

Question 49

Within a group, why is there a decrease in electronegativity as you go down the group?

Answer 49

Because of the increasing size of the atoms (increased shielding and increasing atomic radius) as you go down the group

Question 50

Across a period, why is there an increase in electronegativity?

Answer 50

the increasing nuclear charge decreases the atomic radius

Question 51

What is a "pure" covalent bond?

Answer 51

when the electrons are shared evenly between the two atoms

Question 52

What is a polar bond?

Answer 52

A covalent bond in which there is a separation of charge between one end and the other (when one end is slightly positive and the other end slightly negative.)

Question 53

What is a permanent dipole?

Answer 53

when the opposite charges within a molecule act as poles on either end of the molecule (2 poles = permanent dipole)

Question 54

If one atom is a lot more electronegative than the other, what happens?

Answer 54

The more electronegative atom takes the electrons completely and ions are formed

Question 55

What makes the atoms ionic/completely charged rather than slightly charged?

Answer 55

a difference of more than 0.8 in electronegativity

Question 56

when can ionic bonds showing covalency happen?

Answer 56

- If the positive cation is small and highly charged - if the negative anion is large (so highly polarisable) - dependent on the charge density

Question 57

How can you calculate the charge density?

Answer 57

charge of the ion ÷ ionic radius

Question 58

What does it mean by ionic bonds showing covalency?

Answer 58

If an atom has a high charge density (e.g. aluminium compared to chlorine) then the electron pairs are attracted back to the atom to such an extent that the electrons are partly shared and so the bonds become covalent

Question 59

when does polarising ability increase?

Answer 59

as the positive ion decreases and the number of charges increases

Question 60

What electronegativity difference makes a bond pure covalent?

Answer 60

a difference of 0

Question 61

What electronegativity difference makes a bond polar covalent?

Answer 61

a difference of 0 > 1.8

Question 62

What electronegativity difference makes a bond ionic?

Answer 62

a difference of >1.8

Question 63

What are the types of intermolecular forces?

Answer 63

permanent dipole, london forces, hydrogen bonding

Question 64

What are intermolecular forces?

Answer 64

attractions between one molecule and a neighbouring molecule

Question 65

What is dipole-dipole attraction/bonding?

Answer 65

when molecules line up so the partial positive charges are adjacent to partial negative charges - a net attractive force/weak electrostatic attraction

Question 66

What are the conditions for hydrogen bonding to occur?

Answer 66

- the hydrogen atom must be attached to an atom with high electronegativity (O, N or F) - there must be a lone pair of electrons on the electronegative atom

Question 67

how would the properties of water be different without hydrogen bonds?

Answer 67

- decreased surface tension - Lower boiling point/melting point - ice would be denser than liquid water - water wouldn't stick to itself

Question 68

what are london forces?

Answer 68

the weakest of the intermolecular forces

Question 69

what are london forces also known as?

Answer 69

temporary dipoles/induced dipoles

Question 70

What are monatomic molecules?

Answer 70

molecules of noble gases which consist of a single atom

Question 71

What happens to the strength of london forces as the molecule increases in size?

Answer 71

the number of electrons also increases making the molecule more polarisable and producing greater induced dipole attractions

Question 72

Between molecules with long chains of atoms, do london forces get stronger or weaker? why?

Answer 72

stronger because there are more points of contact.

Question 73

what is the bond strength of a covalent bond?

Answer 73

200-500 kj/mol to break

Question 74

what is the bond strength of a hydrogen bond?

Answer 74

5-40kj/mol to break

Question 75

what is the bond strength of london forces?

Answer 75

2kj/mol to break

Question 76

what happens to iodine crystals with GENTLE heating?

Answer 76

sublimation

Question 77

What are physical properties governed by?

Answer 77

the intermolecular forces

Question 78

why do molecular substances tend to be gases, liquids or have low mpt/bpts?

Answer 78

because the intermolecular forces of attraction are comparatively weak - no covalent bonds need to be broken to melt/boil a molecular substance

Question 79

If a molecule is soluble in water without reacting, what does this suggest?

Answer 79

that the molecule is small and capable of hydrogen bonding or at least is a small very polar molecule

Question 80

if a molecule is a high melting point solid, what does this suggest?

Answer 80

that it is a giant structure (ionic, metallic or giant covalent)

Question 81

if a high melting point solid is soluble in water, what is suggested about the bonding of the solid?

Answer 81

it is ionic

Question 82

if a substance conducts electricity when solid what is suggested about the type of substance it is?

Answer 82

it's either a metal or graphite because delocalised electrons must be present to conduct electricity

Question 83

what is the strength of the intermolecular forces related to?

Answer 83

the number of electrons present and so the size of the molecule (or isolated atom)

Question 84

Which substance will have the higher boiling point out of one polar and one non-polar molecule with the same masses (and so the same number of electrons)?

Answer 84

the polar molecule will have the higher boiling point

Question 85

As you go down a group, how do the strength of the London forces and permanent dipoles compare?

Answer 85

Strength of London forces increases but the strength of permanent dipole decreases

Question 86

When drawing in 3D, how do you express the arrangement of the bonds using different types of lines?

Answer 86

* An ordinary line represents a bond in the plane of the paper (flat) * a dotted line represents a bond going away from you, into the paper * a wedge represents a bond coming towards you, out of the paper

Question 87

What is a key point to remember when drawing ammonium ions in 3D?

Answer 87

The lone pair in ammonium ion is part of a Daitive covalent bond so electrons are still shared, this only counts as one area of electron density