Chemical Bonding and Valence

As acclaimed earlier, the apathetic gas elements of accumulation 8 abide as monoatomic gases, and do not in accepted acknowledge with added elements. In contrast, added aerial elements abide as diatomic molecules (H2, N2, O2, F2 & Cl2), and all but nitrogen are absolutely reactive. Some affecting examples of this acuteness are apparent in the afterward equations.

2Na + Cl2 2NaCl

2H2 + O2 2H2O

C + O2 CO2

C + 2F2 CF4

Why do the atoms of abounding elements collaborate with anniversary added and with added elements to accord abiding molecules? In acclamation this catechism it is adorning to activate with a actual simple archetypal for the allure or bonding of atoms to anniversary other, and again advance to added adult explanations.

Ionic Bonding

When sodium is austere in a chlorine atmosphere, it produces the admixture sodium chloride. This has a aerial melting point (800 ºC) and dissolves in baptize to to accord a administering solution. Sodium chloride is an ionic compound, and the apparent solid has the anatomy apparent on the right. Alteration of the abandoned 3s electron of a sodium atom to the half-filled 3p alternate of a chlorine atom generates a sodium cation (neon valence shell) and a chloride anion (argon valence shell). Electrostatic allure after-effects in these abnormally answerable ions packing calm in a lattice. The adorable armament captivation the ions in abode can be referred to as ionic bonds.

By beat on the NaCl diagram, a archetypal of this clear will be displayed and may be manipulated.

Covalent Bonding

The added three reactions apparent aloft accord articles that are actual altered from sodium chloride. Baptize is a aqueous at allowance temperature; carbon dioxide and carbon tetrafluoride are gases. None of these compounds is composed of ions. A altered adorable alternation amid atoms, alleged covalent bonding, is complex here. Covalent bonding occurs by a administration of valence electrons, rather than an absolute electron transfer. Similarities in concrete backdrop (they are all gases) advance that the diatomic elements H2, N2, O2, F2 & Cl2 additionally accept covalent bonds.

Examples of covalent bonding apparent beneath accommodate hydrogen, fluorine, carbon dioxide and carbon tetrafluoride. These illustrations use a simple Bohr notation, with valence electrons appointed by black dots. Note that in the aboriginal case both hydrogen atoms accomplish a helium-like brace of 1s-electrons by sharing. In the added examples carbon, oxygen and fluorine accomplish neon-like valence octets by a agnate administration of electron pairs. Carbon dioxide is notable because it is a case in which two pairs of electrons (four in all) are aggregate by the aforementioned two atoms. This is an archetype of a bifold covalent bond.

These electron administration diagrams (Lewis formulas) are a advantageous aboriginal footfall in compassionate covalent bonding, but it is quicker and easier to draw Couper-Kekulé formulas in which anniversary aggregate electron brace is represented by a band amid the atom symbols. Non-bonding valence electrons are apparent as dots. These formulas are acquired from the clear notations appropriate by A. Couper and A. Kekulé, and are not identical to their aboriginal drawings. Some examples of such structural formulas are accustomed in the afterward table.

Common Name Molecular Formula Lewis Formula Kekulé Formula

Methane CH4

Ammonia NH3

Ethane C2H6

Methyl Alcohol CH4O

Ethylene C2H4

Formaldehyde CH2O

Acetylene C2H2

Hydrogen Cyanide CHN

Multiple bonding, the administration of two or added electron pairs, is illustrated by ethylene and formaldehyde (each has a bifold bond), and acetylene and hydrogen cyanide (each with a amateur bond). Boron compounds such as BH3 and BF3 are aberrant in that accepted covalent bonding does not aggrandize the valence carapace control of boron to an octet. Consequently, these compounds accept an affection for electrons, and they display aberrant acuteness back compared with the compounds apparent above.

Valence

The cardinal of valence carapace electrons an atom charge accretion or lose to accomplish a valence octet is alleged valence. In covalent compounds the cardinal of bonds which are artlessly formed by a accustomed atom is according to that atom's valence. From the formulas accounting above, we access at the afterward accepted valence assignments:

Atom H C N O F Cl Br I

Valence 1 4 3 2 1 1 1 1

The valences acclaimed actuality represent the best accepted anatomy these elements accept in amoebic compounds. Abounding elements, such as chlorine, bromine and iodine, are accepted to abide in several valence states in altered asleep compounds.

Types Of Bonds

There are thress basic ways in which chemical combination occurs:

(1)    IONLIC  or ELECTROVALENT BOND.

(2)    COVALENT BOND

(3)     COORDINATE BOND.

(1)    IONLIC  or ELECTROVALENT BOND.


    IONLIC  or ELECTROVALENT BOND are formed by transfer of valence electrons from one atom to another. this type of bond unites two atoms one of which has excess electrons than the stable  number (2 or 8) , and the  other is short of electrons. sodium chloride is a typical  compound formed in this way.

Here the sodium atom (2,8,1) transfers its excess electrons to chlorine atom (2,8,7) and thus both attain a  stable inert gas type electron configuration. sodium acquires the electron configuration of neon(2,8) and becomes positively charged chlorine acquires the electrons configuration of argon(2, 8 , 8) and bcomes negatively charged. these oppositely charged ions are held together by electrostatic force of attraction.this type of bond is commonly found in inorganic  compounds.

EXAMPLE...




NOTE THAT

Ionic or electrovalent compounds are non-volatile, soluble in water and possess high melting points. their aqueous solution( aqueous solution are those solution where in inculde in water) conduct electric current.


(2)    COVALENT BOND


COVALENT BOND are formed by mutual sharing of electrons. this type of bond unites two atoms, both of which are short of electrons.
 the two atoms contribute one electron each and share the resulting pair of electrons. HYDROGEN is the simplest  compound formed in this way.

EXAMPLE


THE BOND formed in this way may be single (---- )covalent bond (==) or triple covalent bond (--- =) depending upon the number of shared electrons.such bonds  sre commonly found in organic compounds.

pic...

NOTE THAT.
Covalent compounds are volatile , generally insoluble in water but soluble in organic  solvants. they possess low melting and boiling points.their solution do not conduct  electric current.


(3)     COORDINATE BOND.

coordinate bond is also formed by mutual sharing of electrons but in this case the two electrons that sharred come from the same atom. A coordinate bond unites two atoms, one of which has a spare pair of electrons and the other is short of a pair of electrons. the first atom (donor atom) contributes one pair (lone pair) of electrons and the second atom (acceptor atom) accepts it.after the formation of the bond , the lone pair of electron is held in common. the coordinate bond is represented by an arrow, pointing away from the donor atom.An excellent illustration of the coordinate bond is found in the boron  hydride-ammonia complex .

THE FULL EXPLINATION WITH PICTURE EXAMPLE IS COOMING SOON...............!!!

STRUCTURE OF ORGANIC MOLECULES.

 STRUCTURE OF ATOM.

According to "'Rutherford-bohr" theory ,the atom is made of acentral postively charged nuceus containing positively charged particles called protons, and neutral particles called neutrons. the nucleus is surrounded by negatively charged particles called electrons.

The electrons revolve around the nucleus in fixed orbits or energy levels.while the electron moves in such a level, it possesses a definite quantity of energy and it neither emits nor absorbs energy.the electrons are arranged in the orbits so that the maximum number of electrons in the various orbits starting from the one nearest the nucleus is 2,8,18,32,18,8.the outermost orbit of electrons in different atoms (except inert gases),is incomplete and the electrons in it are known as the ""VALENCE ELECTRONS"".

 WHY ATOMS COMBINE TO FORM MOLECULES? { CHEMICAL BONDS }

The classical concept about the formation of molecule (chemical bond); is based upon the electronic structure of atoms of inert gases have either 2 or 8 electrons in the outermost orbit.the gases do not enter into chemical combination and,therefore, are assumed to have complete or stable orbits.the atoms of all other elements have incomplete outermost orbits and tend to complete them by chemical combination with other atoms.G.N.lewis proposed that it is the urge of atoms to complete their outermost orbit of electrons as in the inert gases, which is responsible for chemical  combination. in other word, chemical combination  between two atoms resulte from the  redistribution of electrons between them so that both the atom complete their outermost orbits or acquire stable electronic configuration possessed by their inert gases.

GENERAL CLASSICCATION OF ORGANIC COMPOUNDS.

Organic compounds cab be classicfiedon the basic of structure as below..

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 1)     OPEN CHAIN COMPOUNDS.

those organic compounds which have open chain  structure are called""OPEN CHAIN COMPOUNDS"". aliphatic compounds or alicyclic compounds. it has two type:

A)   STRAIGHT CHAIN COMPOUNDS.

these compounds have no branch in their structure but may contain single (---),double (==) or triple (= --) bond.

EXAMPLE.
 

 

B)  BRANCH CHAIN.

 these compounds have one or more than one branch in their.

EXAMPLE.

A1)  ISO COMPOUNDS.

     those compounds which have a methylgroup (CH3------) attached to the 2nd last carbon atom of continuous chain.

EXAMPLE.

B2)   NEO COMPOUNDS.

 those compounds which have two methyl (CH3------) group attached to the 2nd last carbon atom of the continuous chain.

EXAMPLE.

2) CLOSE CHAIN COMPOUNDS.

those organic compounds which have cycle or ring in their structure are called "" CLOSE CHAIN ORGANIC COMPOUNDS"".(in these compounds 1st and last carbon atoms are connected with each other.)

EXAMPLE.

There are two types of close chain compounds.
1) HOMOCYCLINC COMPOUNDS.
2) HETROCYCLIC COMPOUNDS.
 
1) HOMOCYCLINC COMPOUNDS.

those compounds in which ring/cycle is made of carbon atom only are called "" HOMOCYCLINC COMPOUNDS   or  CARBOCYCLIC COMPOUNDS"".
EXAMPLE.

there are two types of HOMOCYCLINC COMPOUNDS.
           A) ALICYCLIC COMPOUNDS (Non Benzonide)
          B)  AROMATIC COMPOUNDS.(Benzonide)

 A) ALICYCLIC COMPOUNDS (Non Benzonide)

 the homocyclic compounds having no benzene ring in their structure are called alicyclic compounds.(Ring contain three or more carbon  atomes and resembling aliphatic compounds.)

EXAMPLE.

 B) AROMATIC COMPOUNDS.(Benzonide)
the homocyclic compounds containing at least one or more""BENZENE"" ring in their structure are called  "" AROMATIC COMPOUNDS  or  BENZONIDE COMPOUNDS.""the aromatic compounds have quite a different behaviour from the open chain comounds. all the aromatic compounds have special smell(Aroma).

EXAMPLE.




2) HETROCYCLIC COMPOUNDS.
the cyclic compounds in which ring consiste of atome of more than one kind are called ""HETROCYCLIC COMPOUNDS"" or HETROCYCLES"".

EXAMPLE

SOURCES OF ORGANIC COMPOUNDS.

All organic compounds aat one time came from plants or animals.many of our  most importants substance  are still derived from these sources directly or indirectly.

1) PLANTS AND ANIMALS

     Many organic compounds are obtained directly from plant and animals sources by suitable. method of isllation.a few familiar EXAMPLE are carbohydrates (cellulose, sugar, and starches.) proteins (silk, wool, casein, and food proteins) fats and oils(cottonsed soybean oils lard, butter) alkaloids (quinine ,morphine, strychnine) hormones, vitamins,perfumes, flavours and resins.

2) NATURAL GAS AND PETROLEUM.

             Natural gas and petroleum are now the major sourcse of organic compounds .they are used as fuels  and also, throughsynthetic organic reaction.for the production of hundreds of useful organic substances such as solvents,synthetic rubber,explosive,and plastic.

3)  COAL

           Coal is another major sources of organic compounds.it yield coke and coal-tar on pyrolysis or destructive distillation.more then 200                    organic compounds have been directly isolated from coal-tar. these coal-tar products from the starting materialsfor the manufacture of thousands of useful aromatic compounds,including pefumes,drugs,dyes, photographic developers,and other.

4)  SYNTHESIS.

      Simple organic compunds derived from petroleum or coal have been converted into thousands of useful materials by synthetic mthod.many EXAMPLE might be cited of syntgetic organic compounds replacing those obtained from natural sources,such as dyes, rubber, fibres, plastic ,drugs, vitamins.in many  cases the synthetic materials are superior to the natural compounds replaced.for example ,synthetic dyes are superior to those of natural origin.in other cases the synthetic materials are entirely unknown in nature and fill the requirements not satisfied are entirely other sources.EXAMPLE.are ether .glycol, aspirin, and sulpher drugs.synthetic organicchemistry touches almost every phase of life.

Defination Of FLAMMABLE, COMBUSTIBLE, ISOMERISM,POLYMERISATION,SOLUBILITY,SOLUTE,SOLVENT,CONDUCTER.

1)     FLAMMABLE

The compounds, that catch fire at once,are called or know as'' FLAMMABLE ''

2)    COMBUSTIBLE

The compounds,that burn, are called ''COMBUSTIBLE''

3)     ISOMERISM

The phenomenon in which compounds have same molecular formula but different from each other in physical or chemical properties.

4)    POLYMERISATION

The reaction in which small molecular are combined together to form a big molecule is called ''''POLYMERISATION'''.

5)    SOLUBILITY

The amounte of one substance (solute) that could dissolve in another substance  (solvent) to from a saturated
solution under condition of temerature and pressure.

6)    SOLUTE

A substance that is dissolved in a solvent to from a solution.

7)   SOLVENT

A liquid capable of dissloved other materials(solid , liquid , gas) to from of solution,

8)   CONDUCTER

A substance that CONDUCTER electricity, haet, sound etc through it.

Difference Between Organic and Inorganic Compounds:

Organic and inorganic posses different compostion. nature, structure, and properties.the different between
 organic and inorganic compounds are illustrated from the following statement.

1.} ORGANIC COMPOUNDS.

1..)carbon is basic element of an organic compounds..

e.g .acetic acid (CH3COOH). CH4 (Methane).CCL4 (Carbon tetrachloride.). RNH2.

2..) organic compounds mostly consist of carbon, hydrogen, halogen, and phosphorus.

3..)organic compounds are mostly covalent in nature.

4..)organic compounds  have low solubility in water.

5..)organic compounds sharply soluble in an organic solvent.

6..)organic compounds have low melting and boiling points.

7..) orgain compounds are flammable and combustibe.

8..)organic compounds have a property of isomerism and polymerism.

9..)some organic compounds volatil..e g  Banzane Ether etc.

10..)the reation of oeganic compounds are usually slow.

11.) they  are usually non conductor of electicity.

12.) organic compounds are studied as hydrocarbon and derivative of hydrocarbons. Example : ROH, RX,RNH2,RCHO etc

2.} INORGANIC COMPOUNDS.

1..) carbon is not basic  elements of inorganic compounds.

e.g .NACL(Sodium chloride)..CO2 (Carbon dioxide)..H20 (water)  HCL (Hydrochloric acid)....H2SO4 (Sulfuric acid)

2..) inorganic compounds consist of all the elements known.

3..)inorganic compounds are mostly inonic in nature.

4..) inorganic compounds are heighly soluble in water.

5..) inorganic compounds are not soluble in organic compounds or solvents.

6..)  inorganic compoundshave heigh melting and boiling points.

7..)  inorganic compounds are not flammable and combustible.

8..)  inorganic compounds have no property of isoerism and polymerism.

9..) inorganic compounds are non-volatile.

10.) the reation of inorganic compounds are fast.

11.) they are mostly conucter of electricity.

12.) inorganic compounds are studied as a acid, base and salt.Example  ...H2SO4....NAOH.....NA2CO3...etc