chapter 6 section 2 covalent bonding... pages 178-189 1 modern chemistry chapter 6 chemical bonding...

Chapter 6 Section 2 Covalent Bonding... pages 178-189

1

Modern ChemistryChapter 6

Chemical Bonding

Sections 1-5Introduction to Chemical Bonding

Covalent Bonding & Molecular CompoundsIonic Bonding & Ionic Compounds

Metallic BondingMolecular Geometry


2

Chapte

r V

oca

bula

ryMoleculeMolecular

compoundChemical formulaMolecular formulaBond energyElectron-dot

notationLewis StructureStructural formulaSingle bondMultiple bondResonance


3

Section 2

Covalent Bonding and

Molecular Compounds


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Molecules• A neutral group of atoms that are

held together by covalent bonds• Has all the physical and chemical

properties of the compound• May consist of two or more atoms

of the same element Diatomic elements I2 Br2 Cl2 F2 O2 N2

H2

Molecular elements S8 P4

I Bring Clay For Our New House & Swimming Pool.


5

Formulas• Chemical Formula – indicates

the relative numbers of atoms of each kind in a chemical compound by using symbols and numeric subscripts

• Molecular Formula – shows the types and number of atoms in a single molecule


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Ch

em

ical Fo

rmula

Anim

ati

on


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Formation of Covalent Bondsp

. 1

79


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Formation of a Covalent Bond• Forces to consider

– Electrons repel each other– Protons and electrons attract each

other– e- to p+ attraction is greater than

the e- to e- repulsion


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Formation of a Covalent Bond• Potential Energy and Stability

– High P.E. is related to low stability– Low P.E. is related to high stability


10

Bond Length & Stabilityp

. 1

79


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Characteristics of Covalent Bonds• Bond Length – the distance between

two bonded atoms at their minimum potential energy

• Energy is released when a bond forms

• The same amount of energy is required to break that bond

• Bond Energy – the energy required to break a chemical bond and form neutral atoms.


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Bond Energy & Length Tablep

. 1

82


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Bond L

ength

Anim

ati

on


14

Bond E

nerg

y A

nim

ati

on

p. x

x


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Noble Gas Configurationp

. 1

83


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Octet Rule• Chemical compounds tend to form

so that each atom by gaining, losing or sharing electrons has an octet of electrons in its highest energy level


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Octet Rule Exceptions• Less than 8 electrons

– Boron •Three valence electrons•Stable with only six instead of eight

– Beryllium•Two valence electrons•Stable with only four instead of eight

Always!!Always!!


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Octet Rule Exceptions• Expanded valence - involves the d

orbitals as well as s & p– Phosphorus

•Five valence electrons•Stable with only ten instead of eight

– Sulfur•Six valence electrons•Stable with only twelve instead of eight

Not Always!!

Not Always!!


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Oct

et

Rule

Anim

ati

on


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Lew

is S

truct

ure

s A

nim

ati

on


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Lewis Structures• Formulas in which the

symbols represent nuclei and inner shell electrons, dashes or dot-pairs between symbols represent covalent bonds and dots by one symbol represent unshared pairs.

• Shared pairs = a bond• Unshared pairs = a lone pear


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Lone P

air

Anim

ati

on


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Structural Formula• Indicates the type, number and

arrangement of the atoms and the bonds but not the unshared pairs


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Str

uct

ura

l Fo

rmula

An

imati

on


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How to Draw Lewis Structures1. Do the math to determine the

number of bonds

C H3 I(1 x 8) +(3 x 2) +(1 x 8) = 22 e-

(1 x 4) +(3 x 1) +(1 x 7) = 14 e-

/2 = 4

_

All atoms need 8 electrons to be stable,except H which only needs 2.

All atoms have their valence electrons available for bonding.Subtract the “have” from the “need”.

Divide the total by 2 to get the number of bonds in the molecule.

8 e-


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How to Draw Lewis Structures2. Arrange the atoms as symetrically as

possible, with a central atom.

H

C is the central atom if it is present.H and halogens go on the outside.

ICHH


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How to Draw Lewis Structures3. Connect with bonds.

H

If you have too many bonds, double or triple up.

ICHH


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How to Draw Lewis Structures4. Add unshared pairs so that all

atoms have 8e- (except H)

H

A bond counts as two electrons.

ICHH

Try page 186 #1-4 Practice.


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Multiple Covalent BondsSingle bond: 2 e- are shared by 2 atomsDouble bond: 4 e- are shared by 4 atomsTriple bond: 6 e- are shared by 3 atomsOccur commonly with C, N and O

STRONG single bond SHORT

STRONGER double bond SHORTER

STRONGEST triple bond SHORTESTTable on page 187

Try page 188 #1 & 2 Practice


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Mult

iple

Bonds

Anim

ati

on

p. x

x


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Resonance Structures• Bonding in molecules that

cannot be correctly represented by a single Lewis structure.


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Reso

nance

Anim

ati

on

p. x

x


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Lew

is S

truct

ure

s Pra

ctic

e

• C2Cl4• SCl2• AsF5

• CI2Cl2• BF3

• NO 1-

• CH2O

• IO3 1-


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Section 2 Homework

Chapter 6 Section 2 Worksheet

chapter 6 section 2 covalent bonding... pages 178-189 1 modern chemistry chapter 6 chemical bonding...

Documents

covalent bondforces

covalent bondshas

covalent bondpotential

formation of covalent

bond energy animationp

bond energy length tablep

bond length animationchapter

neutral atoms