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AA IB Chemistry HL > Structure 2.2 - Covalent > Flashcards

Structure 2.2 - Covalent Flashcards

1
Q

What is a covalent bond?

A

electrostatic attraction of the positive nucleii for the region of negatively charged high electron density

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2
Q

How will atoms in a covalent bond achieve a lower energy state?

A

sharing electrons and acquiring a full valence shell

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3
Q

What happens to the bond length as the number of bonds increases?

A

bond length decreases since increasing numbers of electron pairs shared causes the positive nucleii to come closer

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3
Q

What is the octet rule?

A

the filling of the valence shell to achieve 8 electrons

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4
Q

What is the bond energy?

A

a measure of the strength of the electrostatic force of attraction between the atoms
energy required to break the bond

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5
Q

Which are stronger, pi or sigma bonds, and why?

A

sigma are stronger, in a pi bond the electrostatic attraction is off the axis

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6
Q

What are the consequences of pi bonds being weaker?

A

they are more reactive
eg: enable alkenes and alkynes to undergo a wide range of chemical reactions by addition

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7
Q

What are carboxylic acids?

A

homologous series of organic chemicals with the carboxyl group

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8
Q

What is the carboxyl group?

A

COOH

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9
Q

What are the consequences of hybridisation?

A

bonds become shorter, more stable, and more difficult to break

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10
Q

What are electron domains?

A

regions of high electron density surrounding an atom

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11
Q

4 electron domains, no lone pairs

A

Tetrahedral
109.5

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12
Q

4 electron domains, 1 lone pair

A

Trigonal pyramidal
107

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13
Q

4 electron domains, 2 lone pairs

A

Bent
104.5

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14
Q

4 electron domains is always in electron domain geometry

A

tetrahedral

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15
Q

3 electron domains, no lone pairs

A

Trigonal planar
120

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16
Q

2 electron domains

A

Linear
180

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17
Q

3 electron domains, one lone pair

A

Non-linear bent
117

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18
Q

What shapes exist in E.D geometry?

A

ONLY
tetrahedral
trigonal planar
linear
(diatomic)

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19
Q

How does the expansion of the octet occur?

A

elements in the 3rd and lower periods of the p block can promote one or more electrons from a doubly filled s/p orbital into an unfilled d orbital

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20
Q

5 electron domains, no lone pairs

A

trigonal bipyramidal
120 and 90

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21
Q

5 electron domains, 1 lone pair

A

seesaw
<90
<120

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22
Q

5 electron domains, 2 lone pairs

A

T-shape
<90

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23
Q

5 electron domains, 3 lone pairs

A

Linear
180

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24
6 electron domains, no lone pairs
octahedral 90
25
6 electron domains, 1 lone pair
square pyramid <90
26
6 electron domains, 2 lone pairs
square planar 90
27
6 electron domains, 3 lone pairs
T-shape <90
28
6 electron domains, 4 lone pairs
linear 180
29
What is formal charge used for?
to decide which Lewis structure is preferred from several closest to 0 is more preferred
30
What is the formal charge?
the charge an atom would have if all atoms in the molecule had the same electronegativity
31
Formal charge =
number of valence electrons - 1/2(number of bonding electrons) - number of non bonding electrons
32
The preferred Lewis structure would be:
- Formal charge difference closest to 0 - one that has negative charges on the most electronegative ions
33
What needs to happen so that an atom forms covalent bonds from electrons in different sub-orbitals?
1. electrons in the ground state become excited, promoted from an s suborbital to a vacant p suborbital 2. single electrons in different suborbitals become equivalent via hybridisation
34
What is the energy of hybridised orbitals?
intermediate between energies of s and p orbitals
35
What is a sigma bond?
single bond involving one pair of electrons electrons shared in region of space between atoms
36
Structure of a double bond
One sigma bond One pi bond
37
What is a pi bond?
electrons in a region of space above and below the atoms
38
Structure of a triple bond
1 sigma 2 pi
39
What does the type of hybridisation depend on?
on the number of sigma bonds and where the electrons in these bonds came from
40
sp3 hybridisation
4 sigma bonds origination from 1s electron and 3p electrons in excited staye
41
sp2 hybridisation
3 sigma bonds + 1 pi bond origination from 1s electron and 2p electrons in the excited state
42
sp hybridisation
2 sigma bonds from 1s electron and 1 excited p electron and 2 pi bonds
43
Hybridisation in tetrahedral
is always sp3
44
What is delocalization?
a phenomenon that occurs in molecules with 2 or more double bonds in close proximity if a molecule contains 2 or more pi orbitals, they can overlap to form a delocalised pi bond
45
Hybridisation in trigonal planar
sp2
46
Hybridisation in linear
sp
47
What are polar bonds?
unequal distribution of charge between two bonded atoms more electronegative atom will attract electron closer
48
What determines the degree of polarisation
the difference in electronegativity between the two atoms
49
polarity if elements are neighbours to each other on periodic table
weakly polar/non-polar
50
polarity if elements are separated by 2-3 elements on periodic table
strongly polar
50
polarity if elements are separated by 1 element on periodic table
polar
51
polar bond electronegativity
greater than 0 but less than 1.7
52
what must happen for an entire molecule to be polar?
shaped so that the centres of + and - charge are asymmettrically distributed
53
distinct, assymetrical regions of + and - charge on a molecule
they have a dipole
54
how is a molecular dipole shown
arrow pointing towards region of negative charge start of arrow crossed to show positivity
55
3 main types of intermolecular forces of attraction
london forces dipole-dipole forces hydrogen bonding
56
what is van der waals forces
combination of both london and dipole-dipole forces
56
what causes temporary dipoles
movement of electrons in the orbitals of atoms/molecules
57
how are london forces formed
movement of electrons results in formation of a temporary dipole close proximity to another molecule induces a dipole in the other molecule electron cloud becomes distorted and the molecule is polarised temporary and induced dipoles attract each other, forming weak, temporary London force
58
are london forces weak or strong
weak
59
type of intermolecular forces in non polar molecules
may be only london forces, which are the weakest often are gases, or liquids/solids with relatively low m.p and b.p
60
Which factors increase the strength of london forces
increasing number of electrons (molar mass) - the weaker the attraction for the electrons for the nucleus increasing volume of electron cloud increasing contact area between molecules
61
Why do noble gases have low mp and bp
- only have london forces, no intermolecular polar bonds - monoatomic - lower masses and hence number of electrons - weakest form of London force
62
Why does m.p and b.p increase down the noble gas group
atoms increase in mass, increasing in number of electrons and volume of the electron cloud - the strength of london force increases also electrons are further from the nucleus, so the electron cloud is more easily distorted to produce induced dipoles
63
Why are the mps and bps of halogens higher than noble gases
diatomic - 2x the molar mass, more surface area for contact between the molecules, and bigger electron cloud, increased strength of london force
64
Hydrocarbons mp and bp trends
non-polar molecules, only london forces present mp and bp increase as chain length increases because of greater surface area of molecule
65
What is a dipole dipole force
electrostatic attraction between molecules with a permanent dipole
66
Dipole dipole vs london force
dipole dipole is stronger since they are permanent dipoles mp and bp higher in dipole dipole
67
why do substances with dipole dipole have higher mp and bp than only london
because they have both london and dipole dipole forces
68
halogen trends intermolecular forces
as halogen gets bigger, london forces increase, but dipole dipole forces decrease as there is a lower electronegativity b.ps are closer together
69
where does hydrogen bonding occur
- occurs in molecules that have hydrogen covalently bonded to nitrogen, oxygen, or fluorine - N, O and F have lone pairs that can interact with a hydrogen that has a permanent dipole (partial positive charge) - N, O, and F are small and can interact easily with hydrogen
70
what is hydrogen bonding
when an electrongeative atom gets very close to an H atom, tending towards a dative bond, forming an extended network
71
what is chromatography used for
used to separate mixtures of similar substances
72
overview of process of chromatography
small amount of sample is placed on a stationary phase (eg paper) while a mobile phase (eg water) moves through the stationary phase, soaking up the piece of paper as it does so, the sample also moves. the distance it moves depends on the difference btween its attraction to the mobile/stationary phases
73
which molecules move faster in chromatography
molecules more attracted to the mobile phase will move faster and further
74
what affects how far a molecule moves in chromatography
molecule size, shape, polarity and presence of ionic groups
75
= retardation factor
distance travelled by spot/distance travelled by solvent
76
what is a polar solvent
a liquid composed of polar molecules
77
non-polar solvent
a liquid composed of nonpolar molecules
78
polar substances dissolve in...
polar solvents
79
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AA IB Chemistry HL (9 decks)

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