What is Bond in Chemistry? Types of Bonds :-
Chemical compounds are formed by the joining of two or more atoms. Chemical bonds hold molecules together and create temporary connections that are essential to life. A stable compound occurs when the total energy of the combination has lower energy than the separated atoms. Almost 100 years ago, the American chemist Gilbert Lewis proposed that chemical bonds arise from the sharing of pairs of electrons between atoms.
There are three basic ways in which chemical combination occurs :
1. Ionic or Electrovalent bond.
2. Covalent bond
3. Coordinate bonds.
1. Ionic or Electrovalent Bond :
Ionic 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 compounds formed in this way.
Here the sodium atom (2,8,1 ) transfer its excess electrons to chlorine atom (2,8,7) and thus both attain a stable inert gas type electrons configuration. Sodium acquires the electrons configuration of neon (2,8) and becomes Positively charged. Chlorine acquires the electrons configuration of argon (2,8,8) and becomes negative charged. These oppositely charged ions are held togather by electrostatic force of attraction. This type of bond is commonly found in inorganic compounds.
.ionic or Electrovalent compounds are non volatile, soluble in water and possess high melting point their aqueous solution conduct electric current…
2. Covalent Bond :
Covalent bond are formed by mutual sharing of electrons. This Typs of bond unit two atoms, both of which are short of electrons. The two atoms contribute one electrons each and then share the resulting pair of electrons.. Hydrogen is the simplest compounds formed in the way.
Here the two electrons are shared and gIves to each hydrogen atoms the configuration of helium this types of bond is termed covalent bond and is indicated by a line. Covalent bond are commonly found in organic chemistry..
Covalent compounds are volatile, genrally insoluble in water but soluble in organic solvents they posses low melting and boiling points. The solution do not conduct electric current..
3. Co – Ordinate Bond :
Coordinate bonds is also formed by mutual sharing of electrons but in this case the two electrons that are shared comes from the same atoms. A coordinate bond unites two, one of which has a spare pair of electrons and the other is shorts os the pairs os electrons. The first atoms ( donor atoms ) contribute one pair ( lone pair ) of electrons and the second atom ( accsptor atom ) accept it. After the formation of the bond, the lone pair of electrons is held in common. The coordinate bond is represented by an arrow, Pointing away from the donor atom. An excellent illustrated of the coordinate bond is found in the boron hydride – ammonia complex..
Bond Lengths –
When two atoms bonded by a covalent, the distance between the centres of the two nuclei is called bond length.
Bond lengths are measured by X – ray crystallography and by microwave spectroscopy. The unit of bond lengths is angstrom ( 1 Å =10-8 cm ). For most bond the values are the 1 to 2 angstrom. Some typical bond length are given in table..
Bond Energies –
Bond energy or bond strength is defined as the amount of energy required to break a bond in a molecule..
Bond energies depend upon the type of bond as well as the structure environment in which the bond is situated. They are determined by quantitative measurement of head of chemical reaction ( calorimetry ) and by spectroscopy method. The units of bonds energy is kcal / mol. Some typical bond energies are given in table..