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ch 8 notes

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AP Chemistry

Bonding

Intermolecular forces and properties

Bond hybridization

Bonding: General concepts
A chemical bond
No Simple, and yet complete, way to define this
forces that hold groups of atoms together and make them
function as a Unit.
atorns
energy
of the
aggregate
A bond will form if the en
that of the separated atoms *nature favors low energy
-The interaction of 2 hydrogen atoms-
However, we don't want the
.
atoms to get too close.. The
positively charged nuclei will
start to strongly repel each.
other
Potential energy (kJ/mol) –
-
458
www
b
Cengage L
0
0.074
electron
(H-H bond length)
Clouds
reacting
H
Internuclear distance (nm).
a
H atom
is lower than
H atom
Sufficiently far apart
to have no interaction
H atom
H atom
The atoms begin to interact
as they move closer together.
H₂ molecule
Optimum distance to achieve
lowest overall energy of system
Inm= 10.⁹ m Key ideas in bonding
ionic bonding - electrons are transferred ~ donate [0]
[B]
covalent bonding - elections are shared equally by nuclei~ accept
non polar
overlapped orbitals
Polar covalent bond
·
.
·Types of chemical bonds.
.
.
Unequal Sharing of electrons between atoms in a molecule
results in a charge separation in the bond (partial positive and
partial negative charges SH-²F S
St
ST Electronegativity
The ability of an atom in a molecule to attract shared
electrons to itself
Zeff
for a molecule HX, the relative electronegativities of the H
and X atoms are determined by comparing the measured H-X
bond energy with the "expected" H-X bond energy.
on the periodic table, electronegativity general increases across
a period and decreased down a group
the range of electronegativity values is from 4.0 for fluorine
(the most electronegative) to 0.7 for cesium (the least
electronegative)
election shielding
Li Be
No Mg
K Ca S
Rb Sr Y
Cs Ba La
Fr Ra Ac
V Cr
ASPSCI Ar
As Se Br Kr
Sn Sb Te I Xe
2r
Hf To W Re Os i Pt Au Hg Tl Pb Bi Po At Rn
Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
Pa U Np
Md No -The Pauling electronegativity values.
Decreasing electronegativity
Li
10
Na Mg
0.9
1.2
K
0.8
Rb
0.8
Cs
0.7
Be
1.5
Fr
0.7
Ca
1.0
Sr
1.0
Ba
0.9
Ra
0.9
Sc
1.3.
©Cengage Leaming All Rights Reserved
Y
La-Lu
1.0-1.2
Ac
1.I
Ti
1.5
Zr
1.4
Th
13
Hf Ta
13
15
Pa
H
2.1
C-C Zero
V
1.6
C-O Intermediate
Na-Cl Large
Cangage Learning All Rights Reserved
Cr Mn
1.6
1.5
Nb Mo
1.6
1.8
W
1.7
Electronegativity Difference
in the Bonding Atoms
Tc
1.9
Re
1.9
Increasing electronegativity
U Np-No
14
1.4-1.3
Fe
1.8
Ru
2.2
Co
19
Ni
1.9
Rh Pd
22
Os Ir
2.2
2.2
Cu
19
Pt Au
22
24
Bond Type
Covalent
Ag
1.9
Ionic
Polar covalent
Zn
1.6
Cd
1.7
Hg
1.9
B
Al
32 32 32 F3
Ga
C
2.5
Si
1.8
Ge
1.8
Sn
1.8
N
3.0
P
2.1
As
2.0
Sb
1.9
Pb Bi
1.9
1.9
Covalent
character
S
2.5
O
3.5
Se
24
Te
2.1
•Relationship between electronegativity and bond type
Po
2.0
Ionic
character
Cl
3.0
F
40
Br
2.8
I
2.5
At
22 Dipole moment.
Property of a molecule whose charge distribution can be represented
by a center of positive change and Center of negative charge
Use an arrow to represent a dipole moment
point to the negative charge center with the tail of the arrow
indicating the positive center of charge
+
water
497
b
is
A+
S™
4-
esp
map
low e den
density
H
H
High ce No Net dipole moment (dipoles cancel)
28*
b
0-c-0
Electron configurations in stable compounds.
Atoms in stable compounds usually have a noble
gas
electron
configuration Full Ociet
CI-CI:
When 2 nonmetals react to form a covalent bond, they share
electrons in a way that completes the valence electron
configurations of both atoms
When a nonmetal and a representative group metal react to form
a binary ionic compound, the ions form so that the valence electron
configuration of the nonmetal achieves the electron configuration
of the next noble gas atom. The valence orbitals of the metal are
emptied. •Isoelectronic
series.
A series of ions/atoms containing the same number of electrons
O F • Ne• Na • Ma• Apst
ww
Periodic table predictions-
Trends for:
.
.
.
atomic size, ion radius, ionization
renegativity
electron configurations
formula predictions for ionic compounds
covalent bond polarity ranking
Lattice energy = K (Q₁ Q₂)
energy,
Le
No Mg
anions
and electro
BCN
D
Lattice Energy
Change in energy that takes place when separated gaseous ions
are packed together to form an ionic solid
Ps
K= proportionality constant
Q₁ and Q₂ = charges on the ions.
r = shortest distance between the centers of the cations and Sublimation of the solid metal
.
M(g) Cendothermic]
Ionization of the metal atoms
M(g) →→ M+(g) + e- [endothermic]
Formation of an ionic solid.
.
M(S) →
Dissociation of the nonmetal
.
1/2 x₂(g) →) x (g) cendothermic]
formation of nonmetal ions in the gas phase
x(g) + e- →x (g) [exothermic] * election
Formation of the solid ionic compound.
→ MX(S) Cexothermic]
M (g) + X(g)
•Partial ionic character of covalent bonds
No bonds reach 100% ionic character even with compounds that have
max possible electronegativity difference
% ionic character
of a bond ↓
measured dipole moment of X-Y
- Calculated dipole moment of X*Y-
X 100%
Percent ionic character
75
50
25
HI
IBr..
HCI
.HBr
ICI
affinity
1
Lil
KI
Csl KBr
LICI
LiBr
HF.
KCI
NaCl
CsCl
Electronegativity difference
LiF
3
KF
CsF. •fundamental properties of models.
1 A model does not equal reality.
wrong
models are oversimplications, and are therefore often
3 models become more complicated and are modified as they age
4 we must understand the underlying assumptions in a model so
that we don't misuse it
5 when a model is wrong, we often learn much more than when it is
right
•Bond energies
To break bonds, energy must be added to the system.
endothermic,
energy
term carries a positive sign
To form bonds,
energy
is released
exothermic, energy term carries negative sign
AH = [nxD ( Bonas Broken)] - [nxD (Bonds formed)]
.
* represents the bond energy per mole of bonds (always has a
positive sign)
Localized electron Model.
A molecule is composed of atoms that are bound together by
Sharing pairs of electrons using the atomic orbitals of the bound
atoms Localized electron
Model
Electron pairs are assumed to be localized on a particular atom
or in the space between two atoms
lone pairs ~ pairs of electrons localized on an atom
bonding pairs ~ pairs of electrons found in the space between
atoms
1 description of valence electron arrangement (Lewis
.
Structure)
2 prediction of geometry (vespr model)
3 description of atomic orbital types used by atoms to share
electrons or hold lone pairs.
Lewis structures.
Shows how valence electrons are arranged among atoms in a
molecule
Reflects central idea that stability of a compound relates to
noble electron configurations.
gas
Que + rule.
Hydrogen forms stable molecules where it shares two electrons
H.
•H
H
H:H
H Octet rule
Elements form stable molecules when surrounded by eight electrons
·Single/double/triple covalent bonds
Single bond ~ Shares I pair of electrons H-H
Double bond ~Shares 2 pairs of electrons O=C=O
Triple band ~ shares 3 pairs of electrons NEN
Steps for writing Lewis structures.
1 Sum the valence electrons from all the atoms
Ex: H₂O
a(le-) + be- = 8e- total
2 use a pair of electrons to form a bond between each pair of
electrons
H-O-H
3 atoms usually have noble gas configurations. Arrange the
remaining electrons to satisfy the octet rule (or duet rule for
hydrogen)
Ex: H₂O, PB₂, HCN
:Bri
H-O-HP-6
..
Br:
H-CEN: .
.
-Exceptions to octet rule
When it is necessary to exceed the out we for one of several
third-row (or higher) elements, place the extra electrons on the
central atom hypervalent
SF=34e-
As Brg = 40e-
·
F-SIF:
F:
As
Review
• C, N, O, and F Should always be assumed to obey the octet rule
B and Be often have fewer than 8 electrons around them in
•Br:
Br:
their compounds
second row elements never exceed the octet rule
third-row and heavier elements often satisfy the octet rule
but can exceed the octet rule by using their empty valence d
orbitals Resonance
More than one valid Lewis structure can be written for particular
NO₂ = 24 e-
molecules
OO
.
.
.
Ο Ο
N
N
N
O
O
Actual structure is an average of the resonance structures
electrons are really de localized ~ they can move around
entire molecule
||||
OO
41
O
Formal change
used to evaluate non equivalent Lewis structures
atoms in molecules try to achieve formal charges as close to
zero as possible
any negative formal changes are expected to reside on the
most electronegative atoms
Calculating formal charge
1 take sum of the lone pair electrons and one -half the shared
electrons
2 subtract the number of assigned electrons from the number of
valence electrons on the free, neutral atom .
●
VSEPR Model
VSEPR: valence shell electron pair repulsion.
the structure around a given atom is determined principally
by minimizing electron pair repulsion's
1 draw Lewis structure
.
H H
1045°
Two electron pairs are bonding and two are non bonding
the central atom (0) in H2O also has four electron pairs around
it
180°
Two electron pairs
.
2 count electron pairs and arrange to minimize repulsion
3 determine positions.
4 determine name of structure
H:O:HH-O-H
linear
bond
angle
= 180°
3 pairs of electrons
all in same plane
.
Bet₂
.
trigonal planar
angle = 120°
H
Be
1200
120
H
1200
F
Be
6-
B Four electron pairs
tetrahedral
.
.
Four electron pairs
3 bonding pairs
one non bonding pair
trigonal pyramidal
bond
.
angle
.
= 109.5°
angle
●●
N
A
less than 109.5°
H
1077
H
Number of electron pairs
around central atom
4 electron pairs, all bonding:
CH, CF, CF C1, CF₂C1₂
4 electron pairs, three
bonding, one nonbonding:
NH,, PC1,
4 electron pairs, two
bonding, two nonbonding:
H₂O, H₂S
?
Shape of molecule
tetrahedral
Bond
angle
109.5⁰
Triangular pyramid about 107°
bent
about 105° Number of
electron pairs
2
3
4
5
•Electron arrangement
6
Name
linear
trigonal
planar
tetrahedral
trigonal bipy ramidal
Octahedral
Arrangement
000
Jos off gås 4 electron pair arrangements
blo
O
trigonal pyramid
8
tetrahedral
5 electron pair arrangements
trigonal bip yramidal
O
V Shape (bent)
see suw
O
O
linear
I shaped

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Knowunity is the # 1 ranked education app in five European countries

Knowunity was a featured story by Apple and has consistently topped the app store charts within the education category in Germany, Italy, Poland, Switzerland and United Kingdom. Join Knowunity today and help millions of students around the world.

4.9+

13 M

#1

950 K+

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I love this app so much [...] I recommend Knowunity to everyone!!! I went from a C to an A with it :D

The application is very simple and well designed. So far I have found what I was looking for :D

Love this App ❤️, I use it basically all the time whenever I'm studying