Chemical Bonding Flashcards
(113 cards)
1
Q
What are chemical bonds?
A
Electrostatic forces of attraction that exist between particles
2
Q
What is electronegativity?
A
Electronegativity of an atom is a measure of its ability to attract electrons in a bonds
3
Q
How do electronegativity generally change across a period?
A
Increases across a period
4
Q
How do electronegativity generally change down a group?
A
Decreases down a group
5
Q
What bonds do large difference in electronegativity form?
A
ionic bonds
6
Q
What bonds do small or no difference in electronegativity form?
A
covalent bonds (electronegative) or metallic bonds (electropositive)
7
Q
What are metallic bonds?
A
Strong electrostatic forces of attraction between a lattice of positive metal cation and a sea of delocalised mobile valence electrons
8
Q
What is the structure that has metallic bonds?
A
Giant metallic lattice structure
9
Q
What is the nature of metallic bonds?
A
Non-directional
10
Q
What are the factors that affect the strength of metallic bonds?
A
- charge and ionic radius of metal cation
- number of valence electrons metal atom has
11
Q
How does charge and ionic radius affect the strength of metallic bonds?
A
- the greater the charge and the smaller the size of metal cation (greater the charge density)
- stroger the electrostatic forces of attraction between metal cation and delocalised mobile valence electrons
12
Q
How does the number of valence electrons affect the strength of metallic bonds?
A
the larger the mass of valence electrons in the metal atom, the greater the charge of the resultant metal cation and the larger the number of declocalised valence electrons contributed into the sea of delocalised mobile valence electrons
13
Q
What are ionic bonds?
A
strong electrostatic forces of attraction between cations and anions
14
Q
What structure has ionic bonds?
A
Giant ionic lattice structure
15
Q
What is the nature of ionic bonds?
A
Non-directional
16
Q
What is coordinate number?
A
The number of oppositely charged ions surrounding an ion
17
Q
What can ionic bond strength be deduced from?
A
lattice energy of an ionic compound
18
Q
What is lattice energy?
A
Energy released when one mole of solid ionic compound is formed from its constitutent gaseous ions under standard conditions
19
Q
What affects the magnitude of lattice energy?
A
- charges of cation and anion
- ionic radii of cation and anion
20
Q
What is the formula for lattice energy?
A
LE ∝ |Z⁺ × Z⁻ / r⁺ + r⁻|
21
Q
What are covalent bonds?
A
strong electrostatic forces of attraction between nuclei of each atom for the shared pair of electrons
22
Q
What is separation between atoms a fine balance of?
A
- attraction of nuclei for shared electrons
- repulsion between electrons on each atom
- repulsion between positively charged nuclei of each atom
23
Q
What is bond length?
A
distance between the nuclei of atoms involved in a covalent bond
24
Q
How are covalent bonds formed?
A
- electrons involved are both unpaired electrons and located in higher energy orbitals
- electrons are shared such that each atom will attain noble gas configuration
25
What are the exceptions to duplet and octet rule?
* Molecules with central atom that has fewer than 8 electrons in its valence shell, central atom is electron deficient
* Molecules with central atom that has mroe than 8 electrons in its valence shell
26
Why can some atoms accomodate more than 8 electrons in its valence shell?
* expansion of octet occurs due to the presence of vacant, energetically accessible d orbitals
* in excited state electrons gain energy and is promoted to a higher energy orbital
27
What is a sigma bond?
Head-on overlap
28
What is a pi bond?
Sideways overlap
29
Is a sigma bond stronger or a pi bond stronger and what are the implications?
* sigma bond is stronger than pi bond due to more extensive overlap of orbitals in a sigma bond compared to a pi bond
* it is harder to break a single bond compared to one of bonds in double or triple bond
30
What are dative bonds?
Covalent bonds formed when an atom donates a lone pair of electrons into an empty orbital of an electron deficient atom for sharing
31
What happens to two molecules of AlCl₃ in gaseous state?
AlCl₃ monomers form co-ordinate bonds with each other to give rise to dimer Al₂Cl₂
32
What can the strength of covalent bond be deduced by?
bond dissociation energy
33
What is bond dissociation energy?
Enthalpy change when one mole of a particular covalent bond between atoms in a gaseous molecule is broken
34
What is the relationship between strength of covalent bond and bond dissociation energy?
The stronger the covalent bond, the greater the bond dissociation energy
35
What are the factors that affect the strength of covalent bond?
* effectiveness of orbital overlap
* bond multiplicity/order
* polarity of the bond
36
How does effectiveness of orbital overlap affect strength of covalent bond?
the larger the size of bonding atoms, the larger and more diffused the valence orbitals, the less effective the overlap of orbitals and the weaker the covalent bonds
37
How does bond multiplicity/order affect strength of covalent bond?
single bond < double bond < triple bond
38
When does a polar bond arise?
When the atoms contributing electrons to the covalent bond have a difference in electronegativities
39
Usually when will a covalent bond formed be polar?
When the covalent bond is formed between two different atoms with the exception of C and H, S and P, P and H, S and H (Please Have Common Sense)
40
How does polarity of the bond affect the strength of covalent bond?
* dipole moment results in ionic character in covalent bond
* it may increase or weaken the strength of bonds
41
What is giant covalent structure?
Atoms extensively bound together by strong covalent bonds
42
What are some examples of giant covalent structure?
Diamond (C), Si, SiO2, Graphite (C)
43
What is the bonding and structure like in graphite?
* In graphite, each carbon atom in the layer is bonded to 3 other carbon atoms via strong covalent bonds to form a hexagonal arrangement of carbon atoms
* The 4th valence electron of each carbon atom is delocalised between the layers of carbon atoms
* The layers are held together by weak instantaneous dipole-induced dipole forces
44
What are elements or compounds with simple covalent structure like?
* They consist of discrete molecules (covalent molecule with weak IMF)
* These molecules are held together by intermolecular forces that exist between them
* Within the molecules, the atoms of these discrete molecules are held together by strong covalent bonds
45
What is bond angle?
Angle between two bond pairs
46
What are the principles of VSEPR theory?
1. Electron pairs are arranged as far apart as possible to minimise repulsion
2. Lone pair-lone pair repulsion > bond pair-lone pair repulsion > bond pair-bond pair repulsion
3. Multiple bonds are treated as one electron pair
47
What does wedge dash and solid lines each represent?
* wedge: into the paper
* dash: out of paper
* solid line: on the plane of paper
48
What is the shape and bond angle for 2 bond pair, 0 lone pair?
- linear
- 180°
49
What is the shape and bond angle for 3 bond pair, 0 lone pair?
- trigonal planar
- 120°
50
What is the shape and bond angle for 2 bond pair, 1 lone pair?
- bent
- <120°
51
What is the shape and bond angle for 4 bond pair, 0 lone pair?
- tetrahedral
- 109.5°
52
What is the shape and bond angle for 3 bond pair, 1 lone pair?
- trigonal pyramidal
- 107.5°
53
What is the shape and bond angle for 2 bond pair, 2 lone pair?
- bent
- 104.5°
54
What is the shape and bond angle for 5 bond pair, 0 lone pair?
- trigonal bipyramidal
- 120° , 90°
55
What is the shape and bond angle for 4 bond pair, 1 lone pair?
- See-saw
- 120° , 90°
- lone pairs are always placed in equatorial plane to minimise total repulsion
56
What is the shape and bond angle for 3 bond pair, 2 lone pair?
- T-shaped
- 90°
- lone pairs are always placed in equatorial plane to minimise total repulsion
57
What is the shape and bond angle for 2 bond pair, 3 lone pair?
- linear
- 180°
- lone pairs are always placed in equatorial plane to minimise total repulsion
58
What is the shape and bond angle for 6 bond pair, 0 lone pair?
- octahedral
- 90°
59
What is the shape and bond angle for 5 bond pair, 1 lone pair?
- square pyramidal
- 90°
60
What is the shape and bond angle for 4 bond pair, 2 lone pair?
- square planar
- 90°
61
What can affect bond angle if the number of bond pairs and lone pairs are the same around central atom?
* Electronegativities of central and non-central atoms
* atomic size of non-central atoms when comparing with a molecule of same central atom
62
How does electronegativity of central atom affect bond angle?
A more electronegative central atom will draw bond pair electrons closer to itself, increasing the repulsion between bond pairs and hence the bond angle
63
How does electronegativity of non-central atom affect bond angle?
When the non-central atoms are more electronegative, the bond pairs are drawn closer to non-central atom and further away from central atom and thus bond pair-bond pair repulsion decreases and bond angle decreases
64
How does atomic size of non-central atoms affect bond angle?
the larger the atomic size of non-central atom, the greater the repulsion
65
What is a polar molecule?
One that has an overall dipole moment
66
What is a dipole and what kind of quantity is it?
* Distribuition of charge between two covalently bonded atoms of different electronegativities
* vector quantity
67
What is a dipole moment?
Magnitude of dipole for a polar covalent bond (larger dipole moment, more polar covalent bond)
68
What is the order of strength of intermolecular forces (from strongest to weakest)?
* For molecules of similar Mr,
* hydrogen bonds > permanent dipole-permanent dipole interactions > instantaneous dipole-induced dipole
69
What is permanent dipole-permanent dipole interactions?
Weak electrostatic forces of attraction that occur between polar molecules
70
What is the strength of pd-pd affected by?
* Magnitude of net dipole moment
* The larger the magnitude of net dipole moment, the stronger the pd-pd interactions
71
What is instantaneous dipole-induced dipole interactions?
Weak electrostatic forces of attraction that exist between non-polar molecules
72
What affects the strength and extensiveness of instantaneous-induced dipole interactions?
* strength affected by: number of electrons in the molecule
* extensiveness affected by: surface area of molecule
73
How does the number of electrons in the molecule affect the strength of id-id?
The larger the number of electrons in the molecule, the more polarisable is the electron cloud, this results in a larger dipole moment and stronger instantaneous dipole-induced dipole interactions between the molecules
74
How to approximate the number of electrons in a molecule?
Mr
75
How does the surface area affect the extensiveness of id-id interactions?
For molecules with the same Mr, the straight chain molecule compared to branched or spherical molecule has a larger surface area for more extensive instantaneous dipole-induced dipole interactions to be formed with other molecules
76
What are hydrogen bonds?
Weak electrostatic forces of attraction between the protonic hydrogen of one molecule and a lone pair on a highly electronegative atom of another molecule
77
What are the conditions for hydrogen bonds to be present?
- molecules must have one H atom directly bonded to a highly electronegative element (F, O, N)
- neighbouring molecule must have at least one lone pair of electrons on a highly electronegative atom (F, O, N)
78
Why do liquid ethanoic acid have an Mr of 120 while ethanoic acid in aq solution have Mr of 60?
* dimerisation usually occurs when carboxylic acids are in liquid and solid states
* when dissolved in water, hydrogen bonds are formed between acid moelcules and water molecules instead due to large number of water molecules
79
Why does ice have a lower density than water?
* ice adopts an open, crystalline structure with hexagonal holes
* each O atom is surrounded tetrahedrally by 4 H atoms, 2 by covalent bonds and 2 by hydrogen bonds
* this causes molecules to be more widely spaced than in liquid
80
What is the strength of hydrogen bond affected by?
* polarity of H-X bond
* the more polar the H-X bond, the stronger the hydrogen bond
81
Why do metals have a relatively high boiling and melting point?
* Metals have a giant metallic lattice structure
* a large amount of energy is required to overcome the strong electrostatic forces of attraction between the metal cations and the sea of delocalised mobile valence electrons
82
Why do ionic compounds have relatively high boiling and melting point?
* Ionic compounds have giant ionic lattice structure
* a large amount of energy is required to overcome the strong electrostatic forces of attraction between cations and anions
83
Why do substances with giant covalent structures have high melting and boiling point?
For giant covalent structures, large amount of energy is required to overcome the strong and extensive covalent bonds between atoms
84
Why do substances with simple covalent structures have low melting and boiling point?
For substances with simple covalent structure, a small amount of energy is required to overcome the weak pd-pd/id-id/hydrogen bonds holding the discrete molecules together
85
Why do AlCl₃ have a simple covalent structure?
- Al has a high charge density due to its high charge and small radius, thus the cation has a high polairising power
- Chloride ion has a large electron cloud, the electrons are further away from the nucleus and more easily drawn away by a cation of high polarising power, the anion is easily polarised
- the electron density that exists between cation and anion becomes shared between them, giving it its covalent character
86
Why is the boiling point of H2O higher than HF even though H-F bond is more polar that H-O?
- More energy is required to overcome the more extensive hydrogen bonds between H2O molecules than HF molecules
- Extensive of hydrogen bonding is limited by the shortage of hydrogen atoms, not enough hydrogen atoms to bond with all the lone pairs
- In H2O, the extensiveness of hydrogen bonding is maximised by the fact that there are exactly the right numbers of hydrogen atoms and lone pairs so that everyone of them can be involved in hydrogen bonding
87
Why is hydrogen bonding in NH₃ not extensive?
The extensiveness of hydrogen bonding is limited by the fact that each nitrogen atom only has one lone pair, there aren’t enough lone pairs to bond with all the hydrogen atoms
88
Can metals conduct electricity?
metals can conduct electricity at all states
89
Why can metals conduct electricity?
due to the presence of delocalised valence electrons
90
What affects the electrical conductivity of metals?
the greater the number of delocalised valence electrons, the higher the electrical conductivity
91
Can ionic compounds conduct electricity?
ionic compounds can conducty electricity in aqueous and molten state but not in solid state
92
Why do ionic compounds conduct electricity in aqueous and molten state but not in solid state?
* in aqueous and moleten states, ions are mobile
* in solid state, ions are held in fixed positions in the giant ionic lattice structure and are not mobile
93
Can substance with giant covalent structure conduct electricity and why?
* no except graphite
* no mobile charge carriers present, all valence elecrtons are involved in the formation of covalent bonds
94
Why can graphite conduct electricity despite having a giant covalent structure?
graphite can conduct electricity due to the presence of delocalised elecrtons within the layers that allow it to conduct electricity in a direction parallel to the layers
95
Can substance with simple covalent structure conduct electricity and why?
* they do not conduct electricity as there are no mobile charge carriers
* however, aqueous solutions of some simple covalent structures can conduct electricity
96
Do metals have good thermal conductivity and why?
* metals have good thermal conductivity
* When the temperature at one end of a metal is increased, the delocalised valence electrons at the heated end gain kinetic energy and thus greater mobility, they then collide rapidly with other valence electrons at the cooler regions of the metal, transferring kinetic energy from one electron to another
* There is an extensive distribution of delocalised valence electrons throughout the metallic structure allowing kinetic energy to be transferred quickly from one end of the metal to the other end
97
What are the physical properties of metal?
Metal are malleable and ductile
98
What is malleable?
Being able to deform to absorb an impact
99
What is ductile?
Being able to be stretched to great lengths without breaking
100
Why is metal malleable and ductile?
The non-directional nature of the metallic bonds, allow the layers of metal cations to slide over one another without breaking the strong metallic bonds
101
What are the physical properties of ionic compounds?
* hard: A larger amount of energy is required to overcome the strong electrostatic attraction between the cations and anions
* brittle: When a large enough force is applied to an ionic compound, the layers of ions can slide, bringing ions of like charges next to each other and these ions of like charges repel each other and the ionic lattice shatters
102
What are the physical properties of giant covalent structures and why?
* Hard except graphite
* A large amount of energy is required to overcome the strong covalent bonds between the atoms
103
Why is graphite soft and slippery?
A small amount of energy is required to overcome the weak id-id interactions between the layers, allowing the layers to slide over each other
104
What are the physical properties of simple covalent structures and why?
* soft
* A small amount of energy is required to overcome the weak id-id/pd-pd/hydrogen bonds holding the discrete molecules together
105
What is the requirement for solute to be soluble in the solvent?
Energy given out when interactions form between solute and solvent particles is more than the energy taken in to overcome interactions between solute particles and that between solvent particles
105
What are ionic compounds soluble in?
Generally soluble in water and other polar solvents but are insoluble in non-polar solvents
106
Why are ionic compounds soluble in polar solvents?
Ionic compounds can form ion-dipole interactions with water and polar solvents
107
What are ion-dipole interactions?
ion-dipole interactions are electrostatic forces of attraction between charged ions in the ionic compound and oppositely charged dipoles on polar molecules in these solvents
108
Why are ionic compounds insoluble in non-polar solvents?
No favourable interactions between the ions and the molecules of non-polar solvents
109
What is the process of dissolving an ionic compound in water?
1. Ion-dipole interactions form between ions of ionic compound and polar molecules, this process releases energy
2. When the energy released from the formation of ion-dipole interactions is sufficient to overcome the electrostatic attraction between the oppositely charged ions, the ions are ‘removed’ from the crystal lattice and the giant ionic lattice structure starts to break down
3. When all ions are completely surrounded by the water molecules, the ionic compound dissolved
110
What is the solubility of giant covalent structures like?
* Insoluble in all solvents
* Energy released during the formation of solute-solvent interactions is insufficient to overcome the strong covalent bonds between atoms
111
What is the solubility of simple covalent structures like?
* Soluble in solvents of similar polarity
* Molecules in non-polar substances form favourable id-id interactions with molecules in non-polar solvents
* Molecules in polar substances form favourable pd-pd interactions or hydrogen bonds with molecules in polar solvents
112
How do instantaneous dipole-induced dipole interactions arise?
* There is an even distribution of electron density in a non-polar molecule
* at some moment in time, because electrons are continuously moving in their orbitals, there will be asymmetric distribution of electron cloud in one molecule, giving rise to instantaneous dipole in the molecule, this instantaneous dipole induces another molecule nearby
* two molecules become attracted to each other by weak id-id
* as electrons are constinuously moving, asymmetric distribution of electron cloud is lost very quickly, resulting in the lose of instantaneous dipole, however, another instantaneous dipole reforms almost immediately
* net effect of all interactions hold the molecules together
