lecture 5.3 - chemical bonding 1

8/14/2019 Lecture 5.3 - Chemical Bonding 1

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Chemical Bonding

Atoms gain,lose, or shareelectrons inorder to achievea full outer shell

electronconfiguration.


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BondsIonic Bonds

Composed of ions that havegained or lost electrons toachieve a full outer shell

Electrostatic attractive forces

Crystalline solids no discretemolecules - formula units

Identified by empirical formulas

Metal + non-metal

Covalent Bonds

Composed of atoms that

are sharing electrons toachieve a full outer shell

Shared electron bonds

Discrete molecules, formsgases, liquids, and solids

Identified by molecularformulas

Non-metal + non-metal


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Localized ElectronModel

Simple model, easily applied. A molecule is composed of atoms

that are bound together by sharingpairs of electrons using the atomicorbitals of the bound atoms.

Three Parts

1) Valence electrons using Lewis

structures2) Prediction of geometry using VSEPR

3) Description of the types of orbitals


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Lewis Structure Shows how the valence electrons arearranged.

Use dots to represent valence electrons

Ex: Draw the lewis structure of O

O is 1s2 2s2 2p4 6 valence e-


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Lewis Structure Rules

H and He follow the duet rule:

H and He only 2 valence e- to be stable

The rest follow the octet rule:

need 8 valence e- (or none) to be stable

Charged species must be written in [ ]charge #


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[ ]+

Donate e- or Gain e-

[ ]-


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L St t


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F

A stable compound has all its atoms with

a noble gas electron configuration Atoms share bonding paire- to do so

Bonding paire-arebetween the element

symbols A line can represent a bonding paire-

Lew s Structures orCompounds

H FHsingle covalent bondstable

L i El D


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Lewis Electron DotStructures

Bonding electrons pairs electron pairs involved in

bonds

Lone electron pairs electron pairs that do not

participate in bonding

Bond order = number of bonds


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Structures

1.Sumthevalence electrons

Ex: Draw the Lewis structure of O2

6 + 6 = 12 e-

Total e- available for molecule


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2. Connect atoms with a single bond

3. Distribute remaining e- to fulfill all

atoms octet until e- total is reached

Total = 12 e-Used = 2 e-4 e-6 e-8 e-10 e-12 e-

FAIL


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4. If short on e- needed, determine how many

extra bonds are required. Number of extra

bonds = number of electrons needed 2.

Total = 12 e-Used = 4 e-6 e-8 e-10 e-12 e-

success

2 = 1 extra bond required2 e- needed


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O

5. If more than two atoms, the least

electronegative atom is the centralatom.

All other atoms connect to center.

Ex: CO2

C16 val e-

O

6. Satisfy most E.N. (outer) atoms first

All

atoms

happy? FAIL


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O

7. Convert lone e- pairs into bonding e- pairs

until all atoms satisfy octet rule .

(up to a triple covalent bond is possible)

Ex: CO2

C16 val e-

O

First try a double bond

FAIL

Now try another double bond

success

All

atoms

happy?


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for anions add the extra e- to thenumber total e- available

for cations subtract the lost e- fromthe number available

Dont forget [ ] and charge #

8. If molecule is an ion

Ex: CO32-

C O O O22 val e-24 val e-


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Ex: CO32-

C O O O24 val e-

All

atoms

happy?FAIL

Yes,but

2-

success


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Ex: BeH2

B stable with 6 valence e-H Be H

Octet Rule Exceptions

Incomplete octet: stable with less than 8 valence

e-

Be stable with 4 valence e-


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OEx: NO

N can be stable with 7 valence e-

NEx: NO2

ONO

Odd-electron molecules are called radicals

radicals are very reactive


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Expanded Octets

Elements in period 3 or higher have availabled orbitals that may be used to accept

additional electrons if necessary

Ifcentral atom has available d subshell it canhave more than 8 valence e-

Occurs when central atom contacts highly

electronegative elements (halogens & O)

Ex: SF6

Total valence e-

=

48


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SEx: SF6Total valence e-

=

48

Available

3d

subshell

Expanded

octet


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Xe

Ex: XeF4 Total valence e-

=

36

e- remaining

= 36

Step 1 Sum val e-2 Connect

atoms

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3 Distribute

e- to filloctets

2216104

9Apply remaining e-

as lone (or bonding)pairs to central

atom

Apply to corners20

success


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Xe

Ex: XeF4 Instant replay


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breakHW: p. 405 # 61, 62,

64, 65p. 406 # 66, 73,

74

LP: Lab 25 and Lab 6b

lecture 5.3 - chemical bonding 1

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