Folio Kimia(Tiqah..)

8/3/2019 Folio Kimia(Tiqah..)

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SMK Dato Sheikh Ahmad ,

02600 Arau , Perlis.

CHEMISTRY FOLIO

COVALENT BOND

Name :Nur Atiqah bt Rodzi

Form : 4 It 1Teachers name : Zulkifli bin

Hashim

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OBJECTIVE :

1. To study the types of covalent bond.

2. To study the properties of ionic and covalent

compounds.

3.To study the uses of covalent compounds.

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INTRODUCTION

A covalent bond forming H2 (right) where two hydrogen atoms share

the two electrons.

A covalent bond is a form of chemical bonding that is characterized by

the sharing of pairs of electrons between atoms. The stable balance ofattractive and repulsive forces between atoms when they share

electrons is known as covalent bonding.

Covalent bonding includes many kinds of interaction, including -

bonding, -bonding, metal-to-metal bonding, agostic interactions,

and three-center two-electron bonds. The term covalent bond dates

from 1939. The prefix co- means jointly, associated in action,

partnered to a lesser degree, etc.; thus a "co-valent bond", in essence,

means that the atoms share "valence", such as is discussed in valence

bond theory. In the molecule H2, the hydrogen atoms share the two

electrons via covalent bonding. Covalency is greatest between atoms of

similar electron negativities. Although covalent bonding entails sharing

of electrons, it is not necessarily delocalized. Furthermore, in contrast

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to electrostatic interactions ("ionic bonds") the strength of covalent

bond depends on the angular relation between atoms in polyatomic

molecules.

HISTORY

Early concepts in covalent bonding arose from this kind of image of the

molecule of methane. Covalent bonding is implied in the Lewis

structure that indicates sharing of electrons between atoms.

The idea of covalent bonding can be traced several years before 1919to Gilbert N. Lewis, who in 1916 described the sharing of electron pairs

between atoms. He introduced the Lewis notationor electron dot

notationor Lewis dot structurein which valence electrons (those in the

outer shell) are represented as dots around the atomic symbols. Pairs

of electrons located between atoms represent covalent bonds. Multiple

pairs represent multiple bonds, such as double and triple bonds. Some

examples of Electron Dot Notation are shown in the following figure.

An alternative form of representation, not shown here, has bond-forming electron pairs represented as solid lines. While the idea of

shared electron pairs provides an effective qualitative picture of

covalent bonding, quantum mechanics is needed to understand the

nature of these bonds and predict the structures and properties of

simple molecules. Walter Heitler and Fritz London are credited with

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http://en.wikipedia.org/wiki/Ionic_bondhttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Lewis_structurehttp://en.wikipedia.org/wiki/Lewis_structurehttp://en.wikipedia.org/wiki/Gilbert_N._Lewishttp://en.wikipedia.org/wiki/Lewis_Structurehttp://en.wikipedia.org/wiki/Quantum_mechanicshttp://en.wikipedia.org/wiki/Walter_Heitlerhttp://en.wikipedia.org/wiki/Fritz_Londonhttp://en.wikipedia.org/wiki/File:Covalent.svghttp://en.wikipedia.org/wiki/File:Covalent.svghttp://en.wikipedia.org/wiki/Ionic_bondhttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Lewis_structurehttp://en.wikipedia.org/wiki/Lewis_structurehttp://en.wikipedia.org/wiki/Gilbert_N._Lewishttp://en.wikipedia.org/wiki/Lewis_Structurehttp://en.wikipedia.org/wiki/Quantum_mechanicshttp://en.wikipedia.org/wiki/Walter_Heitlerhttp://en.wikipedia.org/wiki/Fritz_London


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the first successful quantum mechanical explanation of a chemical

bond, specifically that of molecular hydrogen, in 1927. Their work was

based on the valence bond model, which assumes that a chemical bondis formed when there is good overlap between the atomic orbitals of

participating atoms. These atomic orbitals are known to have specific

angular relationships between each other, and thus the valence bond

model can successfully predict the bond angles observed in simple

molecules.

GATHERED

INFORMATION

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COVALENT BOND

A covalent bond is a bond that is usually formed between non metal atoms by the sharing of electrons.

Non metals such as hydrogen , carbon ,and oxygen do not lose

electrons from their outer shells. They not form positive ions by

losing electrons. However , their outer shell are incomplete.

Electrons need to be added to the outer shell to attain the

stability of the noble gas atoms.

When the atoms of two non metal reacts , all the atoms need to

gain electrons to complete the octet shell of electrons. They can

do this by sharing electrons between them.

LEWIS STRUCTURE

The Lewis structure of a molecule shows how the valence electrons of

the atoms are atoms of the atoms are arranged in the molecule.

Example:-

(a) A helium atom has two valence electrons. Therefore, its Lewis

structure is as follows.

He :

(b)A neon atom has eight valence electron. Its Lewis Structure is

as follows :

..

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:Ne:

..

Rules for Writing Lewis Structure

1. Add up the valence electrons of all the atoms in the molecule.

Example : CO2The total number of valence electrons of one carbon atom and two

oxygen atoms... .. ..

: C : O : : O :

4 6 6

2. Use a pair of electrons to form a bond between each pair of

atoms.

3. Arrange the remaining electrons to satisfy the duet rule for the

second-row elements.

: O : : C : : O :.. ..

8 electrons for each atom

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Example :

a) A hydrogen atom has only one electrons

b) Its shell can hold two electrons just like the shell in the helium

atom.

c)

h

a shared pair of electrons Bohr model 00

when two hydrogen atoms get close enough, their shells overlap

and they share the electrons as shown above.

d) There is a strong force of attraction between the hydrogen

atoms. This holds them together.

e) This force holding them forms the covalent bond.

H H

4. Molecules such as hydrogen molecules are held together by

covalent bonds.

5. Other molecules that are held together by covalent bonds are

shown in Table 1.

Covalent molecules Formula

Chlorine Cl2

Oxygen O2

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Iodine I2

Nitrogen N2

Sulphur S2

Phosphorus P4

Table 1:~ Covalent molecules and its formula

Single Bond

Chlorinemolecules :~

+

Electrons configuration Bohr molecular model

:~The formation of chlorine

1. A chlorine atoms needs one or more electron to obtain a full

outer shell.

2. When two chlorine atoms come together , they share two of their

outer electrons.

3. In this way , each chlorine atoms will have 8 electrons in outer

shell.

4. The following Lewis structure shows the formation of Cl2.

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. . xx

:c . + x cl x

2.8.7 2.8.7

. . x x

: cl . cl x2.8.8 2.8.8

WATER MOLECULE

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1. The formula of water is H2O.

2. When two atoms of hydrogen and one atom of oxygen get close

together ,they share the electrons in their outer shells.

3. In each molecules , an oxygen atom shares electrons with two

hydrogen atoms. In this way, the following will occur :

a) The oxygen atoms will have eight electrons in its outer shell.

(octet configuration)

b) The hydrogen atoms will each have two electrons in its outer

shell.(duplex configuration)

4. The following Lewis structure shows the formation of the H2O

molecules:

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MENTHANE MOLECULE

1. The formula of methane is CH4 .

2. Carbon is in Group 14 of periodic table. Therefore , the carbon

atoms has 4 electrons in its outer shell.

3. It needs four more electrons to form the octet configuration .

4. To have this configuration , each carbon atom shares electrons

with four hydrogen atoms. The carbon atom will attain the octet

configuration while each hydrogen atom will attain the duplex

configuration.

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AMMONIA MOLECULE

1. The formula of ammonia is NH3 .

2. Nitrogen is in Group 15 of the periodic table and the nitrogen

atoms has 5 electrons in its outer shell.

3. To achieve the octet of electrons , each nitrogen atom needs

another three electrons.

4. When one nitrogen atoms comes together with three nitrogen

atoms , they share their valence electrons .

5. Each nitrogen atoms shares electrons with three hydrogen atoms

as shown in the above diagram .

6. Each hydrogen atoms will have the duplex configuration and the

nitrogen atom will have the octet configuration.

7. The following Lewis structure shows the formation of the NH3molecules.

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TETRACHLOROMETHANE MOLECULE

1. Its formula is CCl4 .

2. Carbon is Group 14 of the periodic table. The carbon atom has

four electrons in its outer shell.

3. To achieve the octet of electrons ,each carbon atom needs

another four more electrons .

4. When one carbon atoms gets together with four chlorine atoms ,

they share their electrons.

5. Each carbon atoms shares electrons with four chlorine atoms as

shown in Figures 5.18.

6. In this way ,each chlorine atom and each carbon atom will have 8

electrons in their outer shells (octet configuration).

7. The following Lewis structure shows the formation of the CCl4molecule :

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DOUBLE BONDSOxygen molecules

1. The formula of oxygen gas 02.

2. Each molecule contains two oxygen atoms.

3. Oxygen is in Group 16 of the Periodic Table. Therefore, it has 6

electrons in its outer shell.

4. To achieve the octet configuration , each atom needs to have

extra 2 electrons.

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5. When two oxygen atoms come together , they share four of their

outer shell electrons as shown in Figure above.

6. The oxygen atoms share two pairs of electrons. This type of bond

is called a double covalent bond or just a double bond.

7. The following Lewis structure shows the formation of the O2

molecules:

Carbon dioxide molecule

1. Its formula is CO2.

2. carbon is in Group 14 of the Periodic Table. It has four electronsin its outer shell.

3. To acrhieve the octet of electrons, each carbon atom needs

another four electrons.

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4. When two oxygen and one carbon atom come together , they

share their electrons as shown in the diagram above.

5. The carbon atom and each of the oxygen atoms will have eight

electrons in their outermost shells.

6. In this way , they achieve the octet stability .

7. The following Lewis structure shows the formation of the CO2

molecules :

TRIPLE BONDSNitrogen Molecules

1. Its formula is N2.

2. Nitrogen is in Group 15 of the Periodic Table. The nitrogen atom

has five electrons in its outer shell.

3. To acrhieve the octet of electrons ,each nitrogen atom needs

another three electrons.

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4. When two nitrogen atoms come together ,they share outer

electrons .

5. Each nitrogens atoms contributes 3 electrons to form three

covalent bonds as shown in the diagrams above .

6. The following Lewis structure shows the formation of the

formation of the N2 molecules:

PROPERTIES OF COVAENT COMPOUNDS

1. Covalent compounds are usually molecules compounds. The

atoms in each molecule are bonded to one another by strong

covalent bonds.

2. However , the attraction between the molecules is weak.

Example :

a) Liquid bromine consists of millions and millions of molecules

of Br2 .

b) In a molecule of bromine there are two bromine atoms. The

atoms are linked to each other by a covalent bond (Br - Br).

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c) This bond is very strong. The strength of this bond is called

the inra molecular bond strength.

d) However , the force of attartion between molecules of Br2in liquid Bromine is very weak.

e) This is called the inter molecular force .

3. In a covalent compounds , the inter molecular force is weak .

the intra molecular force is strong.

4. Covalent compounds usually dissolve in organic solvents but do

not dissolve in water.

5. Covalent compounds in liquid form do not have free ions.

Thus ,they do not conduct electricity.

6. Covalent substance can exist in the form of giant molecules

such as those found in graphite or diamond.

7. Covalent substances.

a) With giant molecules usually have very high melting and

boiling points.b) With simple molecules usually have low boiling and melting

point ,ex: liquid bromine.

CONCLUSIONUses of Covalent Compounds as Solvents

1. Organic solvents usually are liquid organic compounds.

2. Organic solvent usually have simple covalent bonds.

3. The following are organic solvent.

a) Alcohols such as methanol and ethanol

b) Tetrachloromethene

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c) Ether

d) Benzene

e) Trichloromethane

f) Propanone

Organic solvent Uses

Petroleum distillates To make special types of glues

Xylol Used in paints

Alcohols To make synthetic and natural

resins such as shellac

Esters As solvent for lacquers,

includind nail varnish

Ether As a solvent for the

manufacture of some drugs orperfume

Ketones Cellulose lacquers and resins

Cholorinated hydrocarbons Paint stripper and dry

cleaning fluids

Propanone Solvent for varnish and

lacquer

Turpentine Solvent fof paint

Petrol and kerosene Uses as cleaning grease ang oil

Ether and propanone Solvent for perfume

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DISCUSSION

CHARACTERISTIC COVALENT COMPOUNDS

Bond formation By sharing the of electrons between two atom.

Elements Non-metallic with non-metallic

Particles Molecular particles

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Physical states Can be solid , liquid or gas

Melting point Low (usually below 3000 C)

Solubility in water Soluble or insoluble, usually in soluble

Volatility Usually volatile

Conductivity Do not conduct electricity in any form

:- properties of covalent bond

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