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ATOMS ALWAYS UNDERGO CHANGE AND IN DOING SO, THEY COMBINE WITH EACH OTHER,
AND HOLD TO EACH OTHER USING AN INVISIBLE FORCE CALLED A CHEMICAL BOND.
Chemical Bond – invisible force that hold atoms together in a compound.
Rationale : stability : Octet Rule and or Rule of 2
KINDS Results FORMS STRENGHT
E’s are transferred from aMetal to a non metal
With formationOf ions
ElectrostaticAttractionBetweenCation & anion
E’s are shared betweenSeveral non metals
WithoutFormation of ions
ionic
covalent
Attraction betweenThe + charged nucleusAnd the - electronClouds of the bond &Attraction involvingThe opposite spins ofelectrons
Atoms Lewis symbol
Formation of Pertinent Bond
Formula
iA NaVIIA Cl
Transfer of electrons
Na1
ClNaClNa
Cl
IIA CaIIIA N
Transfer of electrons
Ca
N Ca+2
N
-3
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _
+2 -3
LCM= 6_ _ 3_ _ _ _ _ _ _ _ 2_ _ _ _ _ _
+6 -6
Ca3N2
IA HVIIA Cl
Sharing of electrons HCl
H
ClCl
H H
Cl
IA HIVA C
Sharing of electrons CH4
H
CC
H
H
H
H C H
H
H
H
• In bonding, compound formation,
•
• total positive charge = total negative charge
• Total electropositive charge = total electronegative charge
BOND POLARITY
• Arises whenever atoms share their electrons unequally that is whenever they have different electronegativities
Kinds of chemical bonds Basis of sharing of electrons
• Non polar covalent bond
– atoms share their electrons equally; atoms have equivalent electronegativities
• Polar covalent bond-
• atoms share their electrons non equally; atoms have different electronegativities
• Rule :Basis of electronegativity difference (END)
1. If END range is 0 to 0.4 non polar covalent bond
2. If END range is 0.5 to 1.7 to 1.9 – polar covalent bond
3. If END range is >0.5 to 1.7 to 1.9 – ionic bond•
THEORIES OF COVALENT BONDING
1. Valence Bond Theory- Atoms contain orbitals ( with spatial orientations and shapes) that will overlap maximally to form covalent bonds
2. Hybridization Theory- Hybridization- way of trying to modify the orbital model of an atom to explain the existence of bonds that are equivalentMixing of electrons to form hybrid orbitals
Atoms that show multiple covalency numbers will hybridize
• Covalency Number – number of unpaired electrons
• -dictates the number of possible bonds to be formed
LEWIS SYMBOL COVALENCYNUMBER
NUMBER OF FORMEDBONDS
HYBRIDIZED ?
H 11 NO
LEWIS SYMBOL COVALENCYNUMBER
NUMBER OF FORMEDBONDS
HYBRIDIZED ?
Cl1 1
NO
LEWIS SYMBOL COVALENCYNUMBER
NUMBER OF FORMEDBONDS
HYBRIDIZED ?
C4 4
YES
LEWIS SYMBOL COVALENCYNUMBER
NUMBER OF FORMEDBONDS
HYBRIDIZED ?
N3
3YES
LEWIS SYMBOL COVALENCYNUMBER
NUMBER OF FORMEDBONDS
HYBRIDIZED ?
O2 2 YES
Hybrids Orbitals involved
Number of hybrids
Number of pure orbitals
Name of hybrid
Angle of repulsion among hybrids
Angle of repulsion between hybrid and pure orbitals
Sp3 S p p p
4 0 tetrahedral 1090
Sp2 S p p 3 1, (p orbital)
Trigonal planar
1200 900
sp S p 2 2 ( 2 p orbitals)
digonal 1800 900
• Hybridization Rule :• Number of hybrid orbitals formed =number
of pure atomic orbitals used
To predict the type of hybrid of an Atom:
• Single bonds – sp3
• Double bonds – sp2
• Triple bonds - sp
• For Carbon: •
• If C is bonded to 4 other atoms ; sp3• If C is bonded to 3 other atoms ; sp2• If C is bonded to 2 other atoms ; sp
• For N:
• If N is bonded to an sp3 C ; sp3 N• If N is bonded to an sp2 C; sp2 N• If N is bonded to an sp C; sp N
• For O
• If O is bonded to an sp3 C; sp3 O• If O is bonded to an sp2 C; sp2 O
CH3 H
CH2 = CH2
CH CH
1
2
3
CH3 C= O
OH
CH3 C= O
OCH3
sp2
sp2
sp2
sp3
sp2
CH2
H4
5
CH3 N
CN
CO
OCH3
CH3 N
CN
CO
OCH3
sp2
sp2
p
p
sp2
sp2
UNIQUE PROPERTIES OF WATER
• Many of the unusual properties of water are a result of its chemistry
• 1. is a polar molecule, with a positively and negatively areas. It causes H- bonding. Each water molecule can form 4 H-bonds.
• 2. is a bent molecule
Properties Environmental Impact
High boiling point
High heat capacity Allows ocean to have a moderating influence on climate particularly along coastal areasOcean does not experience the wide temperature fluctuations that are common on land
High heat of vaporization As water evaporates it carries the heat with it into the air thus has a cooling effect. The body is cooled when perspiration evaporates from the skin
Less dense at temperature below 4oC (ice) Ice floats on denser liquid water . Because of this water freezes from the top down rather than from the bottom up so that aquatic life can survive beneath a frozen surface
OH
HO
H
H
OH
H
OH
H
OH
H
OH
H
OH
H
OH
H
PREDICTINGMOLECULAR GEOMETRY
PREDICTING MOLECULAR GEOMETRY
uses
Lewis Formula Valence Shell Electron Pair RepulsionSteps; ( VSEPR)1. determine the skeleton structure of the molecule2. be sure to count that the total number of dots is equal to the total number of valence electrons3. surround each atom with 8 dots; except H, with 2 dots
Skeleton structure : (Which atom is bonded to which ?)
ligands Central atomAtom with lower group number
Atomwith lower electronegativity
Atom with higher period number : when the atoms have the same group numbers
NF3
Rationale
It needs more e’s to attain octetN F
F
F
N VA F VIIA
EN 3 EN 4
Atom with higher period number :CENTER ATOM when the atoms have the same group numbers :
SO3
period 3S VI A
O VIA period 2
S O
OO
Cl F3
For molecules add up the valence electrons of the atoms.
In the NF3 , N has five e’s and each F has 7 e’s
(Recall that the number of valence electrons equals the A- group number
For polyatomic ion, add 1 e ‘ for each negative charge, or substract e’ for each positive charge
VSEPRE’ pair aroundCentral atom
MinimumRepulsion
LONE PAIR
Directional property
BOND PAIR
6
2
3
4
5
linear
Trigonal planar
tetrahedral
Trigonal bipyramid
octhedral
suggests Should exert
Can be
with without
when
modifiesRepel in a way to form
3 electron groups
Trigonal planar arrangement
Trigonal planar V shape
2 molecular shapes
is
has
when
All 3 bond pairs 1 lone pair2 bond pairs
4 electron groups
Tetrahedral arrangement
3 molecular shapes
is
has
Tetrahedral V shape
when
pyramidal
All 4 bond pairs1 lone pair 3 bond pairs
2 lone pairs2 bond pairs
5 electron groups
Trigonal bipyramidal arrangement
4 molecular shapes
is
has
Trigonal bipyramidal
linear
when
T- shapeSee- saw
All 5 bond pairs
1 lone pair4 bond pairs
2 lone pairs3 bond pairs
3 lone pairs2 bond pairs
6 electron groups
Octahedral arrangement
3 molecular shapes
is
has
octahedral Square planar
when
Square pyramidal
All 6 bond pairs
1 lone pair5 bond pairs 2 lone pairs
4 bond pairs
N HHH
109.5
107104
Electron pair repulsions cause deviations from ideal bond angle s in the order
Lone pair lone pair repulsion
Lone pair bond pair repulsion
Bond pair bond pair repulsion>>
OHH
equatorialequatorial
axialaxial
lying in a plane lying in a plane
Lying above and below of plane Lying above and below of plane
Five and six electron groups In a molecule with this arrangement , there are 2 types of positions for sorrounding electron groups , and 2 ideal bond angles
12090
90
90
LONE PAIRS OCCUPY EQUATORIAL POSITIONS
The greater the bond angle , the weaker the repulsionRationale
Complete the Table
molecule Lewis Structure Molecular shape
Orbital hybridizatiion of the central atom
P Cl
Cl
Cl
Cl
PCl4 +
VA VII A
tetrahedral
sp3
all 4 bond pairs
P ClCl
ClCl
5X1 =57X4= 28------------ 33 -1=32 - 8 = 24 -24 =0
molecule Lewis structure Molecular geometry
Orbital hybridizationOf the central atom
NO2 -
VA VIA
N OO
BENT SP2N OO
5X1 =56X2 = 12--------------- 17 +1 = 18 -4 = 14 -12 = 2 -2= 0
molecule Lewis structure Molecular geometry
Orbital hybridizationOf the central atom
NF3
VA VII AN F
F
F
5 X1 = 57 X 3 = 21-------------- 26 - 6 = 20 - 18 = 2
Pyramidal
sp3N F
FF