S2.2 - covalent model Flashcards
1
Q
What is the octet rule?
A
Tendency for atoms to gain a valence shell with a total of 8 electrons around the central atom.
2
Q
What is a covalent bond?
A
Electrostatic attraction between a shared pair of negative electrons and a positive nucleus
3
Q
What are the covalent structures?
A
- Giant covalent structure
- Simple molecular structure
4
Q
How do you draw a lewis diagram?
A
- Add up the sum of valence electrons
- Draw a rough structure
- Put a pair of electrons between each atom
- Add pairs to satisfy the octet rule
- Add double bonds if you run out of electrons
- Check to see if the number of electrons is the same as in Step 1
5
Q
What are the exceptions to the octet rule?
A
Be - only needs 4 electrons
B - only needs 6 electrons
H - only needs 2 electrons
6
Q
What is an incomplete octet?
A
When the central atom has less than 8 electrons in its valence shell.
7
Q
What is an expanded octet?
A
When the central atom has more than 8 electrons in its valence shell.
8
Q
What is bond strength?
A
Measure of the energy required to break a bond; usually expressed as lattice enthalpy.
9
Q
What is bond length?
A
A measure of the distance between 2 bonded nuclei
10
Q
What is the relationship between bond length, amount of bonds and enthalpy?
A
Shorter bond length = Higher Bond enthalpy
More bonds = Higher bond enthalpy
More bonds = Shorter bonds
11
Q
What is a double bond?
A
When 4 electrons are shared by 2 atoms
12
Q
What do double bonds contain?
A
One sigma bond and one pi bond.
13
Q
What is a triple bond?
A
When 6 electrons are shared between 2 atoms.
14
Q
What do triple bonds contain?
A
One sigma bond and 2 pi bonds.
15
Q
Why is a double bond not twice as strong as a single bond?
A
Multiple bonds are unequal bonds as they contain different bonds.
- pi bonds are weaker than sigma bonds.
16
Q
What is a dative bond?
A
When one atom donates both electrons
17
Q
What is an example of a dative bond?
A
CO
18
Q
Where does the arrow point?
A
From the donating to accepting atom.
19
Q
What is a coordination bond?
A
A coordination bond is a covalent bond in which both the electrons of the shared pair originate from the same atom.
- Once this bond is formed, it is no different from a covalent or dative bond.
20
Q
Why do lewis acid-bases lead to the formation of a co-ordination bond?
A
When Lewis acids and Lewis bases react, it forms a Transition metal complex, in which the Lewis acid accepts electron pairs from the Lewis base, which donates a non-bonding pair, which forms a coordination bond.
- When they are bonded in a complex, they are known as ligands.
21
Q
How can transition metals act like lewis acids?
A
Transition metals can act like Lewis acids by using orbitals in an unoccupied energy level, such as 4s and 4p, to accept electrons.
22
Q
What kinds of bonds do multiple bonds form?
A
unequal bonds
23
Q
What type of bonds do triple bonds contain?
A
- 1 sigma bond
- 2 pi bonds
24
Q
What type of bonds do double bonds contain?
A
- 1 sigma bond
- 1 pi bond
25
Why is a double bond not 2x stronger than a single bond?
a double bond is made out of 2 different bonds; it contains 1 sigma bond and 2 pi bond, which is weaker
26
What does the VSEPR model do?
Enables the shapes of atoms to be determined form the repulsion of electron domains around a central atom.
27
What is the shape of a molecule determined by?
- Nature of bond
- Amount of electron domains
- Bond angles
28
What is an electron domain?
Areas where electrons (paired or single) are located
29
What are the key points to the VSEPR theory?
- Repulsion applies to all electron domains; single, double or triple bonds.
- The total amount of electrons around an atom determines its geometrical arrangements.
- The shape of the molecule is determined by the angles between bonding atoms.
- Non-bonding pairs and multiple bonds cause more repulsion than a bonding pair (resulting in smaller bond angles).
- Non-bonding pairs have a higher charge concentration as the electrons are not being shared.
- Multiple bonds contain 2 or 3 pairs of electrons.
30
What is the order of pairs from least to most repulsion?
1) Lone pair - Lone pair
2) Lone pair - Bonding pair
3) Bonding pair - Bonding pair
- This is because lone pairs have a higher charge concentration.
31
How do you work out the shape of a molecule?
1. Draw a Lewis Diagram and count the number of electron domains around the central atom.
- Remember: single, double and triple bonds all count as 1 electron domain
2. Electron domains repeal each other to a point of maximum or minimum repulsion
4. Shape of a molecule is determined by bond angles.
5. Bonding pairs repel less than non-bonding pairs.
- Don't have to draw the angles accurately, just label on the diagram.
32
What is the shape and bond angle for a molecule with 2 electron domains?
- Linear shape
- 180
33
What is the shape and bond angle for a molecule with 3 electron domains?
- Triangular planar
- 120
34
What is the shape and bond angle for a molecule with 4 electron domains?
- Tetrahedral
- 109.5
35
What is the shape and bond angle for a molecule with 4 electron domains; 2 bonding and 2 lone?
- Bent v-shape
- 105
36
What is the shape and bond angle for a molecule with 4 electron domains; 3 bonding and 1 lone?
- Trigonal pyramidal
- 107
37
What is the shape and bond angle for a molecule with 3 electron domains; 2 bonding and 1 lone?
- Bent v-shape
- 117
38
How does charge link to repulsion?
Greater charge concentration leads to a greater repulsion and a smaller bond angle
- The bonds are closer to each other but further away from the lone pair.
39
What is polarity?
Difference in the electronegativities of bonded atoms
40
When is a molecule polar or non-polar?
Polar - difference in electronegativity is greater than 0.4
Non-polar - no difference in electronegativity or is smaller than 0.4 (covalent compounds)
41
What is the bond continuum?
Ionic - complete transfer of electrons
Polar covalent - partial transfer of electrons
Covalent - equal sharing of electrons
42
What are the conditions needed for a molecule to be polar?
- Must contain a polar bond (split charge)
- Must be unsymmetrical (bonds would cancel each other out otherwise)
- Alkanes and alkenes are always non-polar.
43
What is the melting and boiling point like for polar and non-polar substances?
Non-polar - as the molecules gets larger, melting and boiling point increases as there are more IMFs.
- Overall, non-polar substances have a lower melting and boiling point than polar substances.
Polar - high melting and boiling point due to strong electrostatic attraction.
44
When do substances dissolve or not dissolve?
Like substances dissolve in like solvents.
Forces between substance > Attraction to water = doesn't dissolve
Forces between substance < Attraction to water = does dissolve
45
What are practical uses of polarity in substances ?
Biological systems are based on polar covalents molecules in aqueous solutions
- Non-polar solvents can remove greasy stains.
46
What does it mean for a molecule to be excited?
The molecule has absorbed IR, meaning that they vibrate at higher frequencies.
47
When will a molecule be IR active?
A molecule will only be IR active if it contains an overall dipole moment related to the position and vibration of the bonds.
48
How can polyatomic molecules be IR active?
- They can achieve an overall dipole moment without a polar bond.
- Polyatomic molecules have multiple modes of vibration such as stretching and bending.
49
How can diatomic molecules be IR active?
- The bond must be polar for it to react with IR.
- Diatomic molecules only have 1 mode of vibration; stretching.
50
What is electronegativity?
Measure of the ability of an atom to attract a pair of electrons in a covalent bond.
51
What are general trends of electronegativity?
- Down the group, electronegativity decreases.
- Across the period, electronegativity increases/
52
What does bond polarity result from?
The difference in electronegativity of bonded atoms.
53
What is a bond dipole?
When a polar bond that has 2 partially separated opposite electric charges.
54
What are pure covalent bonds?
Bonds where the difference in electronegativity in bonded atoms is 0.
55
What are key features of ionic compounds?
- complete transfer of electrons
- lattice of oppositely charged ions
- NaCl, LiF, K2O
56
What are key features of pure covalent compounds?
- equal sharing of electrons
- discrete molecules
- Cl2
57
What are key features of polar covalent compounds?
- partial transfer of electrons
- unequal sharing of electrons
- HF, HCl, HI, HBr
58
What is molecular polarity?
Polarity of a molecules which depends on:
- the polar bond it contains
- molecular geometry
59
What is molecular geometry?
Molecular geometry - ways in which polar bonds are orientated with respect to each other.
60
What is a net dipole?
Net dipole - overall difference between 2 charges (shows net charge on a Lewis diagram).
61
How are electrons transferred?
From the least to the most electronegative atom.
62
When are molecules polar?
If the net dipoles (turning force in an electric field) does not cancel out.
63
What are allotropes?
Allotropes have different bonding and structural patterns of the same element in the same physical state, but have different chemical and physical properties.
64
What is nanotechnology?
Nanotechnology is the use of nanoparticles in technology.
65
What are the properties of silicon dioxide?
- Known as silica or quartz
- Each Si atom has 4 covalent bonds to O atoms
- Each O atom has a covalent bond to 2 Si atoms.
- High melting and boiling point
- Strong
- Insoluble in water
- Doesn't conduct electricity
66
What are the properties of Silicon?
- Tetrahedral arrangement in a giant lattice structure
- Covalent bond with 4 other C atoms
67
What is catenation?
Tendency for carbon atoms to form covalent bonds with other carbon atoms.
68
What is a difference between the network structures of carbon and silicon?
- Carbon has a tendency to form covalent bonds with other carbon atoms.
- Silicon has a tendency to form covalent bonds with oxygen.
69
What are the bond enthalpy comparisons?
C - C = 346
Si - Si = 226
- Carbon has a greater strength bond due to its smaller atomic radius, resulting in greater electrostatic attraction between nuclei and shared pair of electrons.
Si - O = 466 (silica)
70
What is graphene -hBN?
When carbon atoms are replaced by boron and nitrogen.
- Used in insulation, electronics and cosmetics
71
What is the hybridization of diamond, graphite, graphene and C60?
Diamond - sp3
Graphite - sp2
Graphene - sp2
C60 -sp2
72
How many atoms of carbon are diamond, graphite, graphene and C60 bonded to?
Diamond - 4
Graphite - 3
Graphene - 3
C60 - 60
73
What is the shape of diamond, graphite, graphene and C60?
Diamond - tetrahedral
Graphite - hexagon parallel layers
Graphene - hexagon single layers
C60 - sphere
74
What is the bond angle of diamond, graphite, graphene?
Diamond - 109.5
Graphite - 120
Graphene - 120
75
What is the electrical conductivity like for diamond, graphite, graphene and C60?
Diamond - none
Graphite - good conductor
Graphene - good conductor
C60 - low conductivity
76
What is the thermal conductivity like for diamond, graphite, graphene and C60?
Diamond - good
Graphite - not good unless forced to conduct in the direction parallel to the crystal
Graphene - best
C60 - low
77
What is the appearance of diamond, graphite, graphene and C60?
Diamond - transparent, lustrous crystal
Graphite - non-lustrous grey crystalline solid
Graphene - nearly transparent
C60 - black powder
78
What are the properties of diamond, graphite, graphene and C60?
Diamond - brittle and hard
Graphite - brittle, soft and slippery
Graphene - thickness of 1 atom, strong and flexible
C60 - light and strong, reacts with K to make superconducting crystalline material
79
What is the melting point like for diamond, graphite, graphene and C60?
Diamond - very high
Graphite - very high
Graphene - high
C60 - low
80
What are the uses of diamond, graphite, graphene and C60?
Diamond - jewellery, ornaments, machinery
Graphite - lubricants, electrolysis, pencils
Graphene - TEM, photovoltaic cells, touch screens
C60 - lubricants, electronic devices, catalysts and nanotechnology
81
What determines the nature of the forces that exist between molecules?
Size and polarity of the molecules
82
What are intermolecular forces?
IMF - forces of attraction between molecules
83
What are the 3 types of intermolecular forces?
1. London Dispersion Forces
2. Dipole-Dipole bonding and Dipole-Induced-Dipole bonding
3. Hydrogen bonding
84
What are Van Der Waals forces?
1. London Dispersion Forces
2. Dipole-Dipole bonding and Dipole-Induced-Dipole bonding
85
What is an intra-molecular bond?
Forces of attraction within molecules
- Covalent bond between negative electrons and a positive nuclei
86
What are London dispersion forces?
LDF - weakest type of IMF present in all molecules.
- Atoms have a difference of electronegativity between 0 and 0.4
87
How do LDF's form?
1. An electron can move around a molecule
2. At any point in time, an electron will be closer to 1 atom.
3. This causes an instantaneous dipole.
4. Electron from neighboring molecule is repelled.
5. This causes and induced dipole in the neighboring molecule.
6. London Dispersion force is the attraction between the induced and instantaneous dipole.
88
What is an instantaneous dipole?
Split charge caused by the movement of electrons.
89
What is an induced dipole?
Split charge due to a dipole in another molecule.
90
What affects the strength of LDF?
Number of electrons - increased number of electrons increases the strength of the LDF.
91
What is a dipole-dipole attraction?
Middle IMF with attractive forces between 2 dipoles with a permanent charge separation.
- Difference in electronegativity is between 0.4 and 1.8.
92
What affects the strength of dipole-dipole attraction?
Difference in polarity = increased difference in electronegativity means a stronger attraction.
Number of electrons = more electrons means an increased attraction.
93
What is a dipole-induced-dipole?
A molecule with a permanent dipole can induce a dipole in a non-polar molecule to form a bond.
94
What is hydrogen bonding?
Strongest IMF that is a dipole-dipole interaction between H and N,O or F.
- There is a difference in electronegativity greater than 1.8, so bonding electron pairs are pulled away from the H to form air pockets.
95
What elements are involved in hydrogen bonding?
H and N, O or F
96
What is the relationship between polarity and boiling point?
The more polar a bond, the higher the boiling point due to a stronger electrostatic attraction.
97
Why is hydrogen bonding the strongest?
Hydrogen bonding is the strongest as H is a small molecule with no inner electron or shells to interfere.
98
What forces are overcome when substances boil or melt?
When a covalent substance melts or boils, the attractive forces between molecules are overcome, not the bonds within the molecule.
99
How does size affect LDF?
Larger size = more LDF
100
How does polarity affect LDF?
Greater difference in electronegativity = stronger type of LDF present
101
How does size affect the melting and boiling points?
Larger size = larger melting and boiling points due to increased electrons and more LDF's forming, requiring more energy to overcome.
102
Why are covalent substances gases or liquids at room temperature?
The forces that need to be overcome to break the molecules are relatively weak IMF, which are easier to break than the electrostatic attraction in ionic lattices.
103
What is volatility?
Tendency for a substance to vaporize and become a gas.
104
What is the trend of volatility for covalent compounds?
Larger molecules have more LDF's, so require more energy to overcome and are harder to vaporize.
105
What is solubility?
Ability to dissolve a solute in a solvent to form a solution.
106
What is solubility like for a polar/non-polar substance?
Polar - dissolves in polar substances as hydrogen bonding or dipole-dipole bonding forms.
Non-polar - dissolves in non-polar substances as it cannot form the correct IMF.
107
How does size affect solubility?
Larger size = less soluble
Smaller size = more soluble
108
Why does sand not dissolve in the tide?
Sand does not dissolve in the tide as it is a non-polar substance and water is polar, so it doesn't form the correct IMF to dissolve. It also has a giant covalent structure which requires huge amounts of energy to overcome.
109
What is electrical conductivity like for covalent compounds?
Covalent compounds cannot conduct electricity as there are no delocalised electrons to move around the structure and carry charge.
110
What is the volatility, solubility (polar and non-polar solvents) and electrical conductivity like in an ionic compound?
Volatility - low
Solubility in polar solvents - soluble
Solubility in non-polar solvents - non soluble
Electrical conductivity - conducts when molten or dissolved
111
What is the volatility, solubility (polar and non-polar solvents) and electrical conductivity like in a polar covalent compound?
Volatility - higher
Solubility in polar solvent - solubility increases with polarity
Solubility in non-polar solvents - solubility increases as polarity decreases
Electrical conductivity - non conductors
112
What is the volatility, solubility (polar and non-polar solvents) and electrical conductivity like in a non-polar covalent compound?
Volatility - highest
Solubility in polar solvents - non-soluble
Solubility in non-polar solvents - soluble
Electrical conductivity - non-conductors
113
What is the volatility, solubility (polar and non-polar solvents) and electrical conductivity like in a giant covalent compound?
Volatility - low
Solubility in polar solvents - non soluble
Solubility in non-polar solvents - soluble
Electrical conductivity - non conductors (except graphene and graphite as well as Si and fullerenes)
114
What is the mobile phase?
The phase that doesn't move; the paper.
115
What is the stationary phase?
The phase that moves; the solvent.
116
What determines solubility of each compound?
Type of IMF present
- Hydrogen bonds dissolve and move up the paper, but LDF's don't dissolve and move.
117
What do small molecules show in a chromatography?
Small molecules - more soluble - travel further
118
What do large molecules show in a chromatography?
Large molecules - less soluble - move less
119
How does IMF and chromatography work?
- Paper is 10% cellulose and is made out of water
- When placed in water, it absorbs it and forms Hydrogen bonds with OH groups from cellulose.
- Solute rises from the start line with water due to capillary action
- When the solute forms the strongest IMF, it stops moving
120
What is Rf values?
Retardation factor - unique values to identify unknown substances
121
How can you calculate Rf values?
Rf = distance moved by component / distance moved by solvent
122
What is thin layer chromatography?
Silica (SiO2) or aluminica (AlO2) is coated onto glass or metal, containing polar groups to form Hydrogen bonds.
123
When do resonance structures occur?
Resonance structures occur when there is more than 1 possible position for a double bond in a molecule when there is more than 1 possible Lewis structure.
- Shows the multiple possible positions of bonds within a molecule
124
What is delocalization?
Delocalisation is the tendency for electrons to be shared between more than 1 bonding position rather than being held in a specific position.
- It is a characteristic of molecules with multiple bonds.
125
What is a resonance hybrid?
A resonance hybrid uses dashed lines to indicate the electron in a double bond being shared between bonding positions.
126
What can be said about the bond lengths in resonance and hybrid structures (O3)?
- All the bonds are the same length.
- The bond lengths are intermediate between single and double bond values.
127
What is an expanded octet?
When there is more than 8 electrons around a central atom.
128
What are exceptions to the octet rule?
- Small atoms such as Be (4) and B (6) have an incomplete octet.
- Period 3 elements may expand using their d-orbitals in valence shells.
129
What is the structure of Benzene?
Benzene (C6H6) is a symmetrical, cyclic structure arranged in a hexagonal ring, each bonded to a H atom in a triangular planar shape with bond angles of 120/
130
How do the bond lengths compare in Benzene?
- All bond lengths have the same values.
- Bond lengths are intermediate between single and double bonds.
131
What does an electron density map show?
The equal density in the map shows that all bonds between carbon atoms are of equal length.
132
How does Benzene not act like other unsaturated molecules?
The 1:1 ratio of Benzene means that it has a higher degree of saturation compared to other unsaturated compounds such as alkynes and alkenes.
133
What are 4 pieces of evidence on the properties of Benzene?
1. Bond length
2. Hydrogenation reaction
3. Type of reactivity
4. Isomers
134
How can Bond Length illustrate the properties of Benzene?
All C-C bonds are of equal length and intermediate between single and double bonds.
- Each bond contains a share of 3 electrons being bonded between atoms (0.139pm).
135
How can the Hydrogenation reaction illustrate properties of Benzene?
The theoretical value of this reaction (-326) is much higher than the experimental value (-210), meaning that Benzene is more stable than predicted from the Kekule structure.
- Delocalization minimizes repulsion between electrons, giving Benzene a more stable structure and lowering resonance energy (energy that needs to be supplied to overcome the special stability of the delocalized ring structure).
136
How can Reactivity Type illustrate the properties of Benzene?
Benzene is reluctant to undergo addition reactions and instead undergoes substitution reactions.
- It is energetically unfavourable for Benzene to undergo addition reactions as it means the resonance energy would need to be supplied and the product will be less stable. Instead it undergoes substitution reactions which preserve the stable ring structure.
137
How can Isomers illustrate the properties of Benzene?
Only 3 isomers of dibromobenzene exist; 1,2- dibromobenzene, 1,3- dibromobenzene and 1,4- dibromobenzene.
- As Benzene is a symmetrical molecule that is cyclic, there are no alternating double and single bonds, so 2 Br atoms can replace H in 3 configurations.
138
How can period 3 elements become an expanded octet?
Electrons from the 3s orbital can be promoted into empty 3d orbitals which merge to form hybridized orbitals that can hold 6 bonds and 12 electrons.
139
What determines if a molecule is polar or not?
Polarity depends on the mape - it must be asymmetrical, even if it's symmetrical and it contains a polar bond, it is not polar.
140
Why is formal charge used?
They are calculated for each atom in a species and is used to determine which of the several Lewis formulas is preferred.
141
How do you calculate formal charge?
formal charge = number of valence electrons in unbundled atoms - number of electrons assigned to atoms in Lewis structure
142
What is the formula for formal charge?
FC= V- (1/2 B+1)
- Number of valence electrons in the group number
- Number of elections assigned to an ature in the lewis structure is calculated by assuming that 1) an atom has an equal shave of the bunding electron pain even if it is a coordinate bond and 2) an atoms owns its lone pairs completely.
FC = valence electrons - ( half the number of bonding electrons - number of lone electrons)
143
What are equivalent Lewis formulas?
Formulas that contain the same numbers of single and multiple bonds, such as the resonance structures of ozone.
144
What are non-equivalent Lewis formulas?
Formulas that contain different numbers of single and multiple bonds, such as the structures of SO2.
145
Which Lewis formula is generally preferred?
The lewis formulas with the atoms having values for formal charge closes to zero is preferred.
146
What is a sigma bond?
Sigma bonds form when the orbitals overlap end on along an axis.
- Can be with s or p orbitals.
- Can be 2 p-orbitals merging, 2 s-orbitals merging or an s and a p-orbital merging.
- All single covalent bonds are sigma bonds
147
What is a pi bond?
Pi bonds form when 2 p-orbitals overlap sideways.
- The electron density is then normally found above and below the plane.
- All double covalent bonds contain 1 sigma and 1 pi bond.
- All triple covalent bonds contain 1 sigma and 2 pi bonds.
148
What is hybridization?
Mixing atomic orbitals within an atom to form new hybrid orbitals for bonding with intermediate energy. The atom is able to form stronger covalent bonds using these hybrid molecules.
149
What are hybrid atomic orbitals?
Where s and p orbitals merge to form equal orbitals.
150
Why is carbon used to study hybridization?
Carbon has an electronic configuration of 1s2, 2s2, 2p2, meaning that there is space for only 2 electrons, yet Carbon is known to be able to form 4 covalent bonds.
151
What bond is formed with the overlap of a hybrid orbital with any other atomic orbitals?
It always forms a sigma pond.
152
What does Carbon being able to form 4 bonds indicate?
It indicates that the lowest energy, or ground-state electron configuration changes during bonding.
153
What is excitation?
An electron is promoted within an atom to a higher energy level.
154
What happens when carbon forms bonds?
When carbon forms bonds, nn electron within the 2s orbital is promoted to the vacant 2p orbital. The atom now has 4 singly occupied orbitals available for bonding.
- The amount of energy put in to achieve this is more than compensated by the extra energy released on forming four bonds.
155
How does methane (CH4) provide evidence for hybridization?
- When carbon undergoes excitation, there are now 4 singly occupied orbitals, but they are not all the same; there is an s-orbital and a p-orbital, which is at a slightly higher energy level.
- The fact that CH4 has 4 identical C-H bonds suggests that these orbitals have been changed and made equal.
156
How do hybrid orbitals differ from their parental orbitals?
- Different energies
- Different shapes
- Different orientation in space
- Can form stronger bonds by allowing for greater overlap.
157
What is sp3 hybridization made up of?
- Hybridization of 1 s-orbital and 3 p-orbitals to produce 4 things.
158
What is sp2 hybridization made up of?
- Hybridization of 1 s-orbital and 2 p-orbitals to produce 3 things.
159
What is sp hybridization made up of?
- Hybridization of 1 s-orbital and 1 p-orbital to produce 2 things.
160
What is sp3 hybridization?
When carbon undergoes 4 single bonds, it undergoes sp3 hybridization, producing 4 equal hybrid orbitals.
- These orbitals orientate themselves at 109.5°, forming a tetrahedron.
- Each hybrid overlaps with the atomic orbital of another atom forming 4 sigma bonds.
E.g) Methane - CH4
161
What is sp2 hybridization?
When carbon forms a double bond, it forms 3 equal sp2-hybrid orbitals and 1 unhybridized p-orbital.
- The 3 sp2-orbitals orientate themselves at 120°, forming a triangular planar shape.
- Each hybrid orbital overlaps with a neighboring atomic orbital, forming 3 sigma bonds.
- The p-orbital is perpendicular to the plane of the sp2 orbital to form a pi bond, with its characteristic lobes of electron density located above and below the bond axis.
162
What is sp hybridization?
When carbon forms a triple bond, it undergoes sp hybridization, producing 2 equal sp hybrid orbitals.
- The 2 sp-orbitals form a linear shape at 180°.
- The 2 p-orbitals are 90° to each other, forming 2 pi bonds, representing the 4 lobes of electron density around the atom. These coalesce into a cylinder of negative charges around the atom, making the molecule susceptible to attack by electrophilic reactants, which are attracted to the electron-dense regions.
163
What else can undergo hybridization?
Lone pairs can also undergo hybridization.
- For example, in ammonia (NH3), the non-bonding pair on the N atom resides in an sp3 orbital.
164
How can hybridization be used to predict molecular geometry and electron domains?
sp3 = tetrahedral arrangement - 4 electron domains
sp2 = triangular planar arrangement - 3 electron domains
sp = linear arrangement - 2 electron domains
165
How do you work out hybridization using electron domains?
- S orbital always exists
- The number of p-orbitals can vary:
Number of p-orbitals = Number of electron domains - 1
166
What are the 2 types of planar triangular structures?
- Planar triangular
- Bent / V-shaped
167
What are the 3 types of tetrahedral structures?
- Tetrahedral
- Triangular pyramidal
- V-shaped
168
What is the hybridization of benzene?
- Each of the 6 carbon atoms is sp2 hybridized, and forms 3 sigma bonds with angles of 120°, making a planar shape.
- This leaves one unhybridized p-electron on each carbon atom with its dumb-bell shape 90° to the plane of the ring.
- Instead of pairing up to form discrete alternating pi bonds, the p-orbitals overlap in both directions, spreading themselves out evenly to be shared by all 6 carbon atoms.
- This forms a delocalized pi electron cloud in which electron density is concentrated in the 2 doughnut-shaped rings above and below the planar ring.
