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chemistry IB > 2.2- covalent model > Flashcards

2.2- covalent model Flashcards

1
Q

covalent bonding

A

electrostatic attraction between a shared pair of electrons and positively charged nuclei

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2
Q

whats the definition of the covalent bond iself

A

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

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3
Q

whats the region of high electron density

A

space between the atoms where a pair of electrons are shared

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4
Q

atoms forming a covalent bond will achieve a lower energy state by…

A

sharing electrons and have a full valence shell. This can be doen by either forming single double or triple bond

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5
Q

octet rule

A

filling of the valence shell to achieve 8 electrons, this rule can in certain circumstances be broken

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6
Q

electronegativity

A

relative measure of attraction of an atom for a pair of electrons (in a covalent bond)

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7
Q

effective nucleus charge determines

A

the net positive charge pulling these electrons towards the nucleus

electronegativity and ionization energy

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8
Q

whats the hybrid diagram

A

the one with the lines

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9
Q

lewis diagram

A

one with the dots

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10
Q

2 electron domains

A

= linear, andgle= 180
eg. co2

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11
Q

3 electron domains

A

= triognal planar
angle= 120
eg. c2h4 or bf3

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12
Q

3 electron domains
1 lone pair

A

angle= 104.5
because stronger repulsion from lone pairs, forcing bonding pairs closer together
=bent linear
eg.so2

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13
Q

4 electron domains

A

=tetrahedral
angle= 109.5
eg. ch4

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14
Q

4 electron domains
1 lone pair

A

=trigonal pyramidal
angle= 107 due to extra repulsion from lone pair
eg. Nh3

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15
Q

4 electron domains
2 lone pairs

A

=bent
angle= 104.5 even greater repulsion
eg. Oh2

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16
Q

repuslion diagram explain

A

biggest repulsion is between two pairs oflone pair
intermedaite= between lone pai and bonding pair
least between 2 bonding pairs

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17
Q

domain geometry

A

= total number of domains, negatively charged areas with electrons ncluding line pairs

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18
Q

molecular geometry

A

only bonding pair areas

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19
Q

electronegativity

A

ability of atom to draw pair of electrons towards itself in a covalent bond

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20
Q

higher value in pauleen scale means

A

more electronegativ element it is in diatomic molecules electron density shared equally between 2 atoms eg. h2
AS BOTH ATOMS HAVE SAME ELECTRONEGATIVITY VALUE= EQUAL ATTRACTION FOR BODNING PAIR OF ELECTRONS LEADING TO FORMATION OF A COVALENT BOND which is non polar

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21
Q

polar bond

A

when 2 atoms in a covalent bond have different electronegstivity, covalnt bond= polar, electrons are drawn to more electronegative atom, electron distributions is aysemmetric
the less electronegative atom si partially positive charge and more is partially negative harge
bigger the differnece in electronegativity between 2 atoms higher polarity of covalent bond

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22
Q

dipole moment

A

measure of how polar a bond is , arrow points to partilly negative charge

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23
Q

intramoleculer vc inter

A

intra within molecules
inter between seperate moelcules

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24
Q

what are the 3 main intermoleculear forces

A

london (dispersion) force
dipole dipole attraction
dipole induced dipole
hydrogen bonding

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25
london dispersion force
temporary dipole lasts very shortly as electron always moving greater number of electrons= greater likehood of forming this tempoerary dipole greater surface area= more contact adjacent moleculer, greater ability to induce a dipole in adjacent molecule, more london forces
26
dipole dipole attraction
temporary dipole exist in all molecules but also have permenant dipo;e molecules with permanent dipole are also attrcted to each other by permenant dipole dipole bonding which slightly increases the strength of intermolecules attration= slightly higher boiling point than molecules with only london forces only happens in polar molecules
27
dipole induced dipole attraction
some mixtures have both polar and non polar molecules permenant dipole of a polar molecule can cause a temporary seperation of charge on non polar molecuke force acts in addition to london and dipole dipole force
28
hydrogen bonding
strongest intermlecular force special type of permenant dipole dipole bonding to take place species has to have an Oxygen and a nitrogen or fluroine (very electronegative) atom with an available lone pair of electrons and hydrogen attached to it bond is very polarised hydrogen becomes so positively charged it can form bond with lond pair of and O, N, F atom in another molecule
29
Van der waals force
include; london force, dipole induced dipole, dipole dipole, forces occur between molecules (intermolecularly and within molecule (intramolecularly)
30
5 domains
electron domain= trigonal bipyramidal moelcular geometry=trigonal bipyramidal angles=120,90
31
5 domains 1 lone pair
electron domain= trigonal bipyramidal moelcular geometry=see saw angles= <120, <90
32
5 domains 2 lone pairs
electron domain= trigonal bipyramidal moelcular geometry=T shaped angles= <90
33
5 domains 3 lone pairs
electron domain= trigonal bipyramidal moelcular geometry=linear angle=180
34
6 electron domains
electron domain= octahedral moelcular geometry=octahedral angles= 90
35
6 electron domains 1 lone pair
electron domain= octahedral moelcular geometry=square based pyramid angle= <90
36
6 electron domains 2 lone pairs
electron domain= octahedral moelcular geometry=square planar angle= 90
37
formal charge
number of valence electrons- 1/2(number of bonding electrons) - number of non bonding electrons
38
preferred lewis diagram
one in which differnece in formal charge of atoms is closest to 0
39
what are the two main types of molecular orbtials
sigma and pi
40
SP3 hybridisation
1 2s 3 2p
41
SP2 hybridisation
1 2s 2 2p
42
SP hybridisation
1 2s 1 2p
43
covalent bond
electrostatic attraction between a shared pair of electrons and positively charged nuclei or electrostatic attraction of the positive nuclei to the region of negatively charged high electron density occurs between atoms that both have a medium to high electronegativity
44
what is the cotet rule
the tendency of atoms to gain a valence shell with a total of 8 electrons
45
what is a dative bond
a covalent bond in which both electrons of the shared pair originate from the same atom
46
what keeps atoms together in a covalent bond
the positive nucleis electrostatic attraction to the region of negative charged high electron density
47
atoms forming covalent bonds will acheiv a lower energy state because
they share electrons and have a full valence shell, this can be done by forming sinle double or even triple bonds
48
what is the filling of the valence shell to achieve 8 electrons called
octet rule
49
hybrid diagram
lines
50
lewis diagram
dots and crosse
51
electronegativity
relative measure of attraction of an atom for a pair of electrons (in a covalent bond)
52
what does effective nuclear charg determines
electronegativity and ionisation energy
53
hydroxium ion
H3O + small portion of water molecules are dissasociated into protons H+ and hydroxide ions OH-. The protons actually exist as hydroxonium ions, the proton forming a dative bond with an undissociated water molecule
54
why does a quadruple bond not exist
because the huge strain involved in making the fourth bond prohibits it
55
describe trends seen by number of bonds
as number of bonds increases, there is an increase in numbers of negative electron pairs which draws them closer to the positive nucleii, decreasing bond length bigger bond energy as increase in number of bonds,
56
what is bond energy
the measure of the strnegth of the electrostatic force of attracton between the carbon atoms and refers to the energy recquires to break the bond and seperate atoms
57
what are weaker and why, sigma or pi bonds
pi bonds are weaker bonds than sigma bonds because the electrostatic attraction is off the axis
58
as pi bonds are weaker...
they are more reactive enabling the compound to undergo a wide range of chemical reactions by addition
59
ethane
single carbon bonds only a sigma bond
60
ethene
double carbon bonds one sigma bond and one pi bond abve and below sigma
61
ethyne
triple carbon bonds one sigma two pi bonds, above and below, infront and behind
62
what happens due to hybridisation
makes bond shorter, more stable and hence more difficult to break
63
what is the shape of covalent molecules and ions determined by
repulsion between electron pairs and numbers of regions of high electron density surrounding an atom termed electron domains
64
4 electron domains and 2 bonding pairs
domain geometry= tetrahedral molecular geometry= diatomic angle= 180
65
66
j
67
6 bonding electrons and 3 lone pairs
electron domain= octahedral molecular geometry= T-shape angle=<90
68
6 bonding electrons 4 lone pairs
electron domain= octahedral molecular geometry= linear angle=180
69
formal charge
can be used to decide which lewis structure is preferred from several, the formal charge is the charge an atom would have if all atoms in the molecule had the same electronegativity
70
formal charge formula
(number of valence electrons)- 1/2(number of bonding electrons)- (number of non-bonding electrons)
71
in order for an atom to form covalent bonds from electrons in different sub- orbitals two steps need to occur
electrons in their low energy sub-orbitals (ground state) pass through a temporary phase (excited state) where vacant p sub-orbitas become singly occupied by promotion of an s electron (a similar process occur during expansion of an energy level- expansion of the octet) 2. single electron in the different sub- orbitals become equivalent in a process called hybridisation forming new hybrid orbital
72
SP3 electron domain geometry
tetrahedral domain geometry
73
SP2 domain geometry
trigonal planar domain geometry
74
SP
linear domain geometry
75
delocolization
is a phenomenon that occurs in molecules with 2 or more double bonds that are in close proximity to each other. A double bond involves the hybridization of electrons to form sigma and pi bonds. A pi bond results from the overlap p orbitals. electron in pi bonds become delocolised accross whole structure
76
if a molecule contains 2 or more pi orbitals
they can overlap to form a delocalised pi bond
77
resonance energy
due to the lower energy state of the actual structure the expected enthalpy change is higher than the actual enthalpy energy recquired

chemistry IB (13 decks)

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