4/14 chemical bonding and structure Flashcards
1
Q
which elements have ionic bonding
A
metals : non metals
2
Q
which elements have covalent bonding
A
non-metals
3
Q
what elements have metallic bonding
A
metals
4
Q
important point of ionic bonding
A
electron transfer
5
Q
important point of covalent bonding
A
shared pair of electrons
6
Q
important point of metallic bonding
A
sea of deloaclised electrons
7
Q
an ionic bond is…
A
electrostatic attraction
8
Q
a covalent bond is…
A
shared pair of electrons
9
Q
a metallic bond is…
A
sea of delocalised electrons
10
Q
melting point of ionic bond
A
high (must break all ionic bonds)
11
Q
melting point of covalent giant
A
high (must break all covalent bonds)
12
Q
melting point of covalent molecular
A
low (often gas at room temp) must only break intermolecular forces)
13
Q
melting point of metallic
A
high
14
Q
do ionic compounds conduct electricity
A
molten can, solid cannot
15
Q
do covalent compounds conduct electrivity
A
no
16
Q
do metallic compounds conduct electricity
A
yes
17
Q
what is moving when electricity is conducted in ionic
A
the ions as they have been made free to move
18
Q
what is moving when electricity is conducted in metallic
A
the delocalised electrons
19
Q
what is electronegativity
A
the measure of the attraction of the atom for a shared pair of electrons
20
Q
what does the difference in electronegativity determine
A
the type of bonding that takes place between atoms
21
Q
a large difference in electronegativity results in
A
the formation of an ionic bond
22
Q
a small difference in electronegativity results in
A
the formation of a covalent bond
23
Q
≥ 1.8 units type of bonding
A
ionic
24
Q
0.5-1.7 units type of bonding
A
polar covalent
25
0.1 - 0.4 units type of bonding
non polar (weakly polar) covalent
26
0 units type of bonding
pure covalent
27
exceptions to the units type of bonding
C-H and H-F
28
where are non polar covalent bonds used
between atoms that are that same element like molecular oxygen
29
what creates a bond dipole
the unequal sharing of electrons in a covalent bond
30
how do you show a bond dipole
δ+ and δ- signs
31
what are single walled nanotubules made from
graphite sheets
32
what can nanotubules act as
conductors or semi conductors
33
nanotubule properties
high electrical conductivity
high thermal conductivity
very very strong
high strain to failure ratio
34
what has the synthesis of carbon nanotubules enable
a way of controlling chemcial reactions on a very small scale. one end can have a fullerene cap so its closed off
35
what does the octet rule say
the most stable arrangement for an atom is to have eight electrons in its outermost energy level with the electron configuration of a noble gas.
36
what are lewis structures
dot and cross diagrams
37
when are there exceptions to the octet rule
atoms that are stable with less than eight electrons and those that can have an expanded octet (more than eight electrons) in their valence shells.
38
what are the exceptions to the octet rule
hydrogen is stable with 2 in outer shell
boron, beryllium and aluminium (in compounds) are stable with fewer than eight electrons in their outer shell.
atoms in period three and higher can form expanded octets with up to twelve electrons in their valence shell
39
what are atoms that have less than eight electrons in their outer shell
incomplete octets or be electron deficient
40
expanded octets
molecules with central atoms from elements in period 3 can accommodate up to 12 electrons in their valence shells.
41
what does the Valence Shell Electron Pair Repulsion Theory allow us to do
predict the shapes of molecules
42
outline VSEPR
electron pairs in molecules repel eachother and orientate themselves as far away from eachother as possible.
a molecule will adopt the shape that minimises the repulsion between the electron pairs.
electron pairs can either be bonding electrons or non-bonding electrons.
both bonding electrons and non-bonding electrons are collectively known as electron domains.
43
what counts as one electron domain
single, double and triple covalent bonds.
44
what is a bonding domain
an electron domain that contains bonding pairs of electorns
45
what is a non bonding domain
an electron domain that contains non-bonding electrons
46
what are non bonding pairs of electrons also known as
lone pairs
47
order of repulsion between non-bonding and bonding domains
Non-bonding domain–non-bonding domain > non-bonding domain–bonding domain > bonding domain–bonding domain
48
where is the greatest repulsion between
between non-bonding domains (lone pairs of electrons), with the second being between non-bonding domains and bonding domains and the least repulsion being between bonding domains.
49
what type of molecular geometry do molecules with two electron domains around the central atom have
linear
50
what is the bond angle of linear molecular geometry
180 degrees, allowing the electrons to be as far apart as possible, which minimises the repulsion between the molecule.
51
what type of molecular geometry do molecules with three electron domains have
trigonal planar. this can either be trigonal planer or bent, depending on the presence of lone pairs of electrons.
52
how is bent molecular geometry caused
by the stronger repulsion that exists between the non - bonding electrons on the central atom compared to the weaker repulstion that exists between the bonding electrons
53
what is the bond angle for trigonal planar
120 degrees
54
a molecule or ion that has a lone pair of electrons on the central atom of a trigonal planar molecule will have a bond angle of...
just under 120 degrees, e.g 117.5
55
what type of molecular geometry do molecules with four electron domains have
tetrahedral electron domain geometry. the molecular geometry can either be tetrahedral, trigonal pyramidal or bent, depending on the number of lone pairs of electrons present.
56
what type of molecular geometry do molecules with four electron domains have with no lone pairs of electrons
tetrahedral
57
what type of molecular geometry do molecules with four electron domains have with one pair of lone electrons
trigonal pyramid
58
what type of molecular geometry do molecules with four electron domains have with two lone pairs of electrons
bent
59
what bond angle do molecules with four electron domains have with no lone pairs of electrons
109.5
60
what bond angle do molecules with four electron domains have with one pair of lone electrons have
107
61
what bond angle do molecules with four electron domains have with two lone pairs of electrons
104.5
62
why do bond angles become progressively smaller
because of the stronger repulsion between the lone pairs and the bonding pairs on the central atom
63
how can there be molecules with five and six electron domains around the central atom
certain atoms in period 3 onwards can expand their octets due to more availability of d orbitals
64
what is the type fo molecular geometry for atoms with five electron domains
trigonal bipyramid
65
what is the type of molecular geometry for atoms with six electron domains
octahedral
66
what bond angle do molecules with six bonding domains have
90 and 180
67
what type of molecualr geometry do molecules with five bonding domains and one non-bonding domain around the central atom have
square pyramidal
68
what bond angle do molecules with five bonding domains and one non-bonding domain around the central atom have
less than 90, due to extra repulsion between bonding and non bonding domains around the central atom.
69
what type of molecualr geometry do molecules with four bonding domains and two non-bonding domain around the central atom have
sqaure planar
70
what type of molecular geometry do molecules with five electron domains have
trigonal bipyramid
71
what bond angle do do molecules with five electron domains have
90 and 120
72
what type of molecular geometry do molecules with five electron domains have and one lone pair of electrons
see saw
73
what type of molecular geometry do molecules with five electron domains have and three lone pairs of electrons
T-shaped
74
what type of molecular geometry do molecules with five electron domains have and three lone pairs of electrons
linear
75
what bond angle do molecules with five electron domains have and one lone pair of electrons
90 and 120
76
what bond angle do molecules with five electron domains have and two lone pair of electrons
less than 90
77
what bond angle do molecules with five electron domains have and three lone pair of electrons
180
78
electron domain geometry of an atom with 6 electron domains and no non-bonding domains
octahedral
79
electron domain geometry of an atom with 6 electron domains and one non-bonding domain
octahedral
80
electron domain geometry of an atom with 6 electron domains and two non-bonding domains
octahedral
81
molecular geometry of of an atom with 6 electron domains and no non-bonding domains
octahedral
82
molecular geometry of an atom with 6 electron domains and one non-bonding domain
square pyramidal
83
molecular geoemtry of an atom with 6 electron domains and two non-bonding domains
square planar
84
what is the bond angle of a molecule with 6 electron domains with no non bonding domains
90
85
intermolecular
between seperate molecules
86
intramolecular
within molecules, eg covalent bonds, attraction between atoms
87
when do london forces increase
when there are more electrons in the molecule
88
what are london forces referred to
van de waals
instantaneous dipole
dispersion forces
89
how are instantaneous dipoles created
when molecules approach one another and their electron cloud repel each other and create an instantaneous dipole
90
are dipole dipole forces more or less strong than the london forces
more
91
a bigger dipole makes for...
a stronger interaction
92
when do hydrogen bonds occur
when a H atom is directly bonded to a NOF
93
what is special about NOF
they are the most electroegative
94
why does hydogen bonding only occur when directly bonded to a NOF
NOF are very electronegative and pull the electron away from the H giving it a poitive charge/induced dipole.
the H can interact with a lone pair on the NOF atom. this is the strongest type of intermolecular force.
95
what is the order of strength for forces
london forces
96
what type of force do all molecules have
london forces
97
properties of metals
good conductors of heat and electricity,
ductile (can be made into wires),
malleable (can be bent into shape) and
shiny when polished.
98
describe the electrons in metallic bonding
delocalised. can flow and carry charge throughut the substance.
99
describe metallic bonding
The metal atoms are ionised, forming positive ions that are arranged in a lattice structure. The bonding in metals, the metallic bond, is defined as the electrostatic attraction between the lattice of positive metal ions and the 'sea' of delocalised electrons. Metallic bonding, like ionic bonding, is described as being non-directional, as the force of attraction occurs in all directions between the positive ions and delocalised electrons within the lattice structure.
100
what is a metallic bond
the electrostatic attraction between the lattice of positive metal ions and the sea of delocalised electrons
101
how are metals malleabel
the layers of positive ions can slide over eachother without disrupting the metallic bond.
102
how are metals ductile
the layers of positive ions can slide over eachother without disrupting the metallic bond.
103
what does being ductile mean
drawn into wires essentially
104
what causes high thermal and electrical condcutivity of metals
the delocalised electrons
105
how do metals conduct electicity
When a potential difference (voltage) is applied across a metal, a direction is imposed on the movement of the delocalised electrons. They are repelled from the negative electrode and move towards the positive electrode. This orderly flow of delocalised electrons in a given direction constitutes the flow of an electric current.
106
how do metals conduct heat
The delocalised electrons can also conduct heat: the electrons move through the metal, carrying kinetic energy (in the form of vibrations) from the hotter part of the metal to the colder part of the metal. These delocalised electrons are also responsible for the shininess of metals, because they reflect wavelengths of visible light.
107
what effects metal's melting points
the ionic charge: greater number of delocalised electrons increases force of attraction between nuclei and sea
the ionic radii: stronger force of attraction between nuclei and delocalsied electrons
108
why are alloys stronger than pure metals
the differently sized atoms in the alloy means that the layers cannot slide over each other as easily
109
brass composition
copper
zinc
110
bronze composition
copper
tin
111
mild steel composition
iron
carbon
112
stainless steel composition
iron
chromium
nickel
113
solder composition
tin
lead
114
alloys are usually
stronger
more chemically table
more resistant to corrosion
115
what type of solvent is water
water molecules are polar (and there are hydrogen bonds between molecules)
116
what type of solvent are alkanes
non polar
(and there are van der waals / london dispersion forces between the molecules)
117
solubility of ionic compounds in water
many ionic compounds dissolve in water
this is because attractions form between the polar water molecules and the ions.
118
solubility of ionic compounds in alkanes
insoluble
119
solubility of compounds with hydrogen bonding in water
usually dissolve in water.
water has hydrogen bonds and substances with hydrogen bonds can form attractions through hydrogen bonds to the water molecules
120
solubility of compounds with hydrogen bonding in alkanes
usually insoluble or only slightly soluble
121
solubility of non polar substances in water
usually insoluble or only slightly soluble
122
solubility of non polar substances in alkanes
usually dissolve well, intermolceular forces form between the solvent and solute molecules.
123
what is the general phrase of solubility
like dissolves like
124
electron geometry is
arrangement of electron pairs around the central atom excluding lone pairs
125
molecular geometry is
arrangement of atoms including lone pairs
126
what elements can accomodate more than eight electrons in their valence shells
period 3
127
why can period 3 elements have expanded octets
due to the availability of d orbitals which can be used for bonidng
128
how is signam bond formed
by the direct head-on (axial) overlap of atomic orbitals. Figure 1 shows the bonding between two hydrogen atoms in a molecule of hydrogen. The two 1s atomic orbitals overlap head-on, forming a sigma bond.
129
where is electron dnesity in a sigma bond
in the region directly between the nuclei of the bonding atoms; this can also be described as cylindrical symmetry along the bond axis (Figure 2). This allows free rotation around a σ bond.
130
sigma bonds can be formed by
head on overlap of two s orbitals
s and p orbitals
or two p orbitals
131
how are pi bonds formed
sidequas overlap of atomic orbitals (two unhybridised p orbitals)
132
double bond is formed from
one sigma bond and one pi bond
133
tripe bond is formed from
one sigma bond and two pi bonds
134
which is the stronger bond pi or sigma
sigma (from the greater overlap of atomic orbitals
135
FC =
(number of valence electrons) - 1/2(number of bonding electrons) - (number of non-bonding electrons
v-1/2B-L
136
what are delocalised electrons
electron shared between more than two nuclei. originate from the overlap of pi bonds in a molecule or ion.
137
carbonate ion
The carbonate ion is a polyatomic ion consisting of a central carbon atom bonded to three oxygen atoms in a trigonal planar arrangement. The bonds between the carbon and oxygen atoms are sigma bonds formed by the head-on overlap of atomic orbitals. A pi bond is formed by the sideways overlap of the p orbitals on the carbon atom and one of the oxygen atoms. The remaining electrons in the p orbitals of the other two oxygen atoms can overlap with the π orbital (of the pi bond), creating a delocalised pi system (Figure 1). These delocalised pi electrons are spread over all three bonding positions, lowering the energy of the molecule (known as the resonance energy
The intermediate nature of the bonding in the carbonate ion, represented by the dotted lines in the resonance hybrid structure (Figure 2), is explained by the formation of the delocalised π system located above and below the plane of the ion.
138
ethanoate ion
In the ethanoate ion, the delocalised π system extends only in the COO− region. Note that this delocalisation of pi electrons does not take place in the ethanoic acid molecule, because one oxygen atom in the carboxyl group is bonded to a hydrogen atom. The resonance hybrid structure of the ethanoate ion is shown in Figure 4. The delocalised electrons are represented by the dashed lines that extend over the COO− region.
139
benzene
The benzene molecule has six carbon atoms, each with a single hydrogen atom attached, in a trigonal planar arrangement. The carbon atoms are sp2 hybridised, each with an unhybridised p orbital (note that hybridisation is covered in more detail in section 14.2.1). As with all molecules with delocalised π electrons, benzene can be represented by different resonance structures. The delocalised π system in benzene contains six electrons, one from each of the unhybridised p orbitals in the carbon atoms. These p orbitals overlap to form a delocalised π system located above and below the plane of the benzene ring (Figure 5).
140
ethanoate ion resonance
141
carboante resonsance hybrid
142
3 possible resonance structures fo rcarboante
143
how are all reonance structure of carbonate equal energy
Each of the three resonance structures contributes to the hybrid structure depending on its energy, with the resonance structure with the lowest energy contributing the most to the hybrid structure. Because of their symmetry, the three resonance structures of the carbonate ion are all of equal energy and they make equal contributions to the resonance hybrid, referred to as equivalent resonance structures.
144
which structures are the msot stable
resonance hybrid always
145
The difference in energy between the resonance hybrid structure and that of the most stable resonance structure is known as
the resonance energy
146
nitrite and nitrate ion resonance hybrid structure.
nitrite then nitrate
147
elements in perido 3 and beyond can
can accommodate more than eight electrons in their valence shells. This is due to the availability of d orbitals which can be used for bonding.
148
how many electrons can sulfur hold in its outer shell
12
149
resonance structures of sulfate
150
resonance structure of ozone
151
Without human influences, the concentration of ozone in the atmosphere remains constant, because
the rate of production of ozone is equal to its rate of destruction.
152
what speeds up ozone depletion
human-made pollutants such as CFCs and nitrogen oxides disrupt this process, causing the phenomenon of 'ozone depletion'.
153
give the equation for trichlorofluromethan edecomposing
CFCl3 → •CFCl2 + Cl• (occurs in the presence of UV radiation)
154
give the equation for the cataluytic cyle breaking down ozone to form diatomic oxygen molecules
Cl• + O3 → ClO• + O2 and ClO• + O• → Cl• + O2
155
equation for overall ozone catayltic cycle (mergin og equations)
O3 (g) + O• (g) → 2O2 (g)
156
where are nitrogen ozides produced
int he stratoshere in jet engines
157
equations for nitrogen oxids in ozone
N2 (g) + O2 (g) → 2NO• (g)
Nitrogen monoxide reacts with ozone as follows:
Step 1: NO• (g) + O3 (g) → NO2• (g) + O2 (g)
Step 2: NO2• (g) + O• (g) → NO• (g) + O2 (g)
combine
O3 (g) + O• (g) → 2O2 (g)
