AM Ikatan Kimia

8/10/2019 AM Ikatan Kimia

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When Atoms Meet


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Bonding Forces

Electronelectron

repulsive forces

Nucleusnucleus

repulsive forces

Electronnucleus

attractive forces

Bonds

Forces that hold groups of atoms

together and make them function as a

unit.


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Metals and Nonmetals


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Types of Chemical Bonding

1. Metal with nonmetal:

electron transfer and ionic bo nding


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Three models of chemical bonding

Electron transfer

Ionic


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2. Nonmetal with nonmetal:

electron shar ing and covalent b onding


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Electron transfer Electron sharing

Ionic Covalent


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2. Nonmetal with nonmetal:

electron shar ing and covalent b onding

3. Metal with metal:

electron pool ing and metal l ic bo nding


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Electron transfer Electron sharing Electron pooling

Ionic Covalent Metallic


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The outer shell electrons of an atom

Participate in chemical bonding

1A 1ns1

2A 2ns2

3A 3ns2np1

4A 4ns2np2

5A 5ns2np3

6A 6ns2np4

7A 7ns2np5

Group # of valence e-e-configuration

Valence Electrons


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G. N. Lewis

Developed the idea in1902.

Lewis Structures


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Nitrogen, N, is in Group 5A and therefore has 5 valence

electrons.

N:

.

..

:

N .. .

.N :.

.:

N ...

Place one dot per valence electron on each of the four

sides of the element symbol.

Pair the dots (electrons) until all of the valence electrons are

used.

Lewis Dot Symbols


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Lewis Dot Symbols


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The OctetRule

Chemical compounds tend to form so that each

atom, by gaining, losing, or sharing electrons, haseightelectrons in its highest occupied energy

level.

The same number of electrons as in the nearestnoble gas

The first exception to this is hydrogen, which

follows the duet rule.The second exception is helium which does not

form bonds because it is already full with its

two electrons


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Li + F Li+ F -

Ionic Bond

1s22s11s22s22p5 1s21s22s22p6[He][Ne]

Li1s 2s 2p

F

1s 2s 2p

+

Li+

1s 2s 2p

F-

1s 2s 2p

+


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Lattice energy (E) increases

as Q increases and/oras r decreases.

cmpd lattice energy

MgF2

MgO

LiF

LiCl

2957

3938

1036

853

Q= +2,-1

Q= +2,-2

r F< r Cl

Electrostatic (Lattice) Energy

E = kQ+Q-

r

Q+is the charge on the cation

Q-is the charge on the anion

r is the distance between the ions

Latt ice energy(E) is the energy required to completely separate

one mole of a solid ionic compound into gaseous ions.


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A chemical bond in which two or more electrons are shared by

two atoms.

How should two atoms share electrons?

F F+

7e- 7e-

F F

8e- 8e-

F F

F F

Lewis structure of F2

lonepairslonepairs

lonepairslonepairs

single covalent bond

single covalent bond

Covalent Bond


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Distribution of electron density of H2

H H


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8e-

H HO+ + OH H O HHor

2e- 2e-

Lewis structure of water

Double bondtwo atoms share two pairs of electrons

single covalent bonds

O C O or O C O

8e- 8e-8e-double bonds double bonds

Triple bond

two atoms share three pairs of electrons

N N

8e-8e-

N N

triple bondtriple bond

or


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H F FH

A covalent bond with greater electron density around

one of the two atoms

electron rich

regionelectron poor

region e-riche-poor

d+ d-

Polar Covalent Bond


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Electron density distributions in

H2, F2, and HF.

El t ti iti (EN)


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Electronegativities (EN)

The ability of an atom in a molecule to attract shared electrons to itself

Linus Pauling

1901 - 1994

Cl ifi ti f B d


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Covalent

share e-

Polar Covalent

partial transfer of e-

Ionic

transfer e-

Increasing difference in electronegativity

Classification of Bonds

Difference in EN Bond Type

0 Covalent2 Ionic

0 < and


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Classify the following bonds as ionic, polar covalent,

or covalent: The bond in CsCl; the bond in H2S; and

the NN bond in H2NNH2.

Cs 0.7 Cl 3.0 3.0 0.7 = 2.3 Ionic

H 2.1 S 2.5 2.5 2.1 = 0.4 Polar Covalent

N 3.0 N 3.0 3.0 3.0 = 0 Covalent

Classification of Bonds


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1. Draw skeletal structure of compound showing what

atoms are bonded to each other. Put leastelectronegative element in the center.

2. Count total number of valence e-. Add 1 for each

negative charge. Subtract 1 for each positive

charge.

3. Use one pair of electrons to form a bond (a single

line) between each pair of atoms.

4. Arrange the remaining electrons to satisfy an octetfor all atoms (duet for H), starting from outer atoms.

5. If a central atom does not have an octet, move in

lone pairs to form double or triple bonds on the

central atom as needed.

Rules for Writing Lewis Structures


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Write the Lewis structure of nitrogen trifluoride (NF3).

Step 1 N is less electronegative than F, put N in center

F N F

F

Step 2

Count valence electrons N - 5 (2s2

2p3

) and F - 7 (2s2

2p5

)5 + (3 x 7) = 26 valence electrons

Step 3 Draw single bonds between N and F atoms.

Step 4 Arrange remaining 20 electrons to complete octets


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Write the Lewis structure of the carbonate ion (CO32-).

Step 1 C is less electronegative than O, put C in center

O C O

O

Step 2

Count valence electrons C - 4 (2s2

2p2

) and O - 6 (2s2

2p4

)-2 charge 2e-

4 + (3 x 6) + 2 = 24 valence electrons

Step 3 Draw single bonds between C and O atoms

Step 4 - Arrange remaining 18 electrons to complete octets

Step 5 The central C has only 6 electrons. Form a double bond.

2-


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More than one valid Lewis structures can be written for a

particular molecule

The actual structure of the carbonate ion is an average of the

three resonance structures

O C O

O

- -O C O

O

-

-

OCO

O

-

-

Resonance

2- 2- 2-


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Exceptions to the Octet Rule

The Incomplete Octet

H HBeBe 2e-

2H 2x1e-

4e-

BeH2

BF3

B 3e-

3F 3x7e-24e-

F B F

F

3 single bonds (3x2) = 6

9 lone pairs (9x2) = 18Total = 24


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Exceptions to the Octet Rule

Odd-Electron Molecules

N 5e-O 6e-

11e-

NO N O

The Expanded Octet (central atom with principal quantum number n > 2)

SF6S 6e-

6F 42e-

48e-S

F

F

F

F

F

F

6 single bonds (6x2) = 12

18 lone pairs (18x2) = 36

Total = 48

C l t B d L th


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Bond

Type

Bond

Length

(pm)

C-C 154

CC 133

C

C 120

C-N 143

C

N 138C

N 116

Covalent BondLengths

Bond Lengths

Triple bond < Double Bond < Single Bond

Covalent Bond Energy


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The energy required to break a particular bond in one mole of

gaseous molecules is the bond energy.

H2 (g) H (g)+ H (g) 436.4 kJ

Cl2 (g) Cl (g)+ Cl (g) 242.7 kJ

HCl(g) H (g)+ Cl (g) 431.9 kJ

O2 (g) O (g)+ O (g) 498.7 kJ O O

N2 (g)

N(g)

+ N(g)

941.4 kJ N N

Bond Energy

Bond Energies

Single bond < Double bond < Triple bond

Covalent BondEnergy


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Contoh : O C O

tot= 0

H2O HOH

CO2 Non polar

Polar

Molecular Shape

VSEPR

Valence Shell Electron-pair Repulsion


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Vibrational Modes of Water

Infrared light

Infrared Spectrum of Water


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Infrared Spectrum of Water

100015002000

Wavenumber (cm-1)

Absorbance

100020003000

Liquid

Gas

Reveal the interactions between molecules and their environments

Infrared Spectrum of Caffeine


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Infrared Spectrum of Caffeine

100020003000

Wavenumber (cm-1)

Absorbance

Identification of compounds


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Acknowledgment

Some images, animation, and material have been taken from the following sources:

Chemistry, Zumdahl, Steven S.; Zumdahl, Susan A.; Houghton Mifflin Co., 6th Ed., 2003;

supplements for the instructor

General Chemistry: The Essential Concepts, Chang, Raymon; McGraw-Hill Co. Inc., 4th

Ed., 2005; supplements for the instructor

Principles of General Chemistry, Silberberg, Martin; McGraw-Hill Co. Inc., 1st Ed., 2006;

supplements for the instructor

NIST WebBook: http://webbook.nist.gov/

http://www.lsbu.ac.uk/water/vibrat.html

http://en.wikipedia.org/wiki/Caffeine

http://www.wilsonhs.com/SCIENCE/CHEMISTRY/MRWILSON/Unit%204%20Chemical%2

0Bonding%20Powerpoint1.ppt

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