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Chemical combination , Types of bonds

From Online Sciences - February 2, 2018

The most stable atoms are those of noble gases such as helium , neon , argon ..etc , Because their outermost energy level is completely filled with electrons , so , the atoms of these electrons do not undergo any chemical reaction ( at normal conditions ) with other elements or with each , their molecules are monoatomic .

Chemical reaction concept

All of the other elements are reactive to some extent , They undergo chemical reactions to complete their outermost shell by accepting , losing or sharing a number of electrons to acquire an identical electron configuration as that of the nearest noble gas .

As the results of this change in the number of electrons in outermost shells of atoms , bonds are formed between atoms or bonds are broken to form new bonds , this is called a chemical reaction , Chemical reaction is the breaking of bonds between atoms of the reactants molecules to form new bonds between atoms of the products molecules .

Application on the chemical reaction concept : The mixture of iron filings with sulphur powder is not considered a chemical compound , because there is no chemical reaction occurs between them , If this mixture is heated to a high temperature , a chemical reaction occurs ( formation of chemical bond ) between iron & sulphur producing the compound iron ( II ) sulphide .

Lewis electron-dot symbols

The valence electrons have an important role in the nature of the formed bond , So , the scientist Lewis had set a simple way to represent the valence electrons by using dots :

Application : Dot-representation of the valence electrons of the oxygen atom 8O

The electron configuration of oxygen atom : 1s , 2s , 2p4 , At the first , the valence electrons are distributed singularly on the four sides of the symbol , then pairing takes till completing the configuration .

The scientist Lewis had differentiated between the lone pair & bond pair of electrons , Lone pair is the electron pair which is found in one of the outer orbitals and does not share in bond formation , Bond pair is the electron pair which is responsible for the bond formation .

Types of bonds

Bonds are divided into Chemical bonds ( Ionic bond , Covalent bond , Coordinate bond ) and Physical bonds ( Hydrogen bond , Metallic bond ) .

Chemical bonds

Ionic bond

This bond is usually formed between the elements of the two terminals of the periodic table which are :

Metals : They are characterized by their large atomic volumes and their low ionization energies , Therefore , Their atoms tend to lose the electrons of the outermost shell and change into cations ( positive ion ) with an identical electron structure to the nearest noble gas precedes them in the periodic table .

Nonmetals : They are characterized by their small atomic volumes and their high electron affinities , Therefore , Their atoms tend to gain electrons ( those lost by metal atoms ) and change into anions ( negative ion ) with an identical electron structure to the nearest noble gas follows them in the periodic table .

Consequently , an electrostatic attraction occurs between the positive cations and the negative anions which is known as the ionic bond , The ionic bond has no materialistic existence .

The ionic bonding and electronegativity

The properties of compounds differ according to the difference in electronegativity between their elements , The difference in electronegativity between the bonded elements play a role in the characteristics of the ionic bond , whereas the horizontal distance between the bonded elementsin the periodic tableincreases , the difference in electronegativity increases , then the strength of ionic bond increases .

In general , when the difference in electronegativity is more than 1.7 then the formed compound is ionic , The ionic bond is the chemical bond which is formed between metals and nonmetals , the difference in electronegativity between them is more than 1.7 .

Molten sodium chloride conducts electricity more than molten magnesium chloride , because the ionic bond in NaCl is stronger than that of MgCl2 , where the difference is electronegativity between sodium and chlorine is greater than that between magnesium and chlorine atoms .

Although chlorine is a nonmetal and aluminum is a metal , aluminum chloride shows the properties of the covalent compounds , Because the difference in electronegativity between aluminum and chlorine atoms is less than 1.7 .

Covalent bond

Classification of covalent bond
Pure covalent bond
Non-polar covalent bond
Polar covalent bond
Application : The polar covalent bond in the hydrogen chloride molecule HCl

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