Chemical bonds

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



HYBRIDIZED ?

Cl1 1

NO



HYBRIDIZED ?

C4 4

YES



HYBRIDIZED ?

N3

3YES



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



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

Technology

Chemical bonds