Chemical Bonding

What is a Chemical Bond?

A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electrostatic force of attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction.

Ionic bond: Ionic bond is one in which one or more electrons from one atom are removed and attached to another atom, resulting in positive and negative ions which attract each other.

Example of Ionic Bond- Formation of NaCl i.e Common Salt or Sodium Chloride

Condition of Ionic Bond

•    Ionization energy of metal should be low
•    Electron affinity of non metal should be high.

Properties of Ionic Compounds

State - Due to strong forces of attraction, all the ionic compounds are exist in solid state.
Thermal Stability -   Ionic compounds have high melting points and boiling points.

Conductance - They are strong electrolytes.In solid state they do not conduct electricity.But in molten state and in   aqueous solution they conduct electricity.

Solubility - Generally ionic compounds are soluble in water and in many polar solvents. Ionic compounds are insoluble in the organic compounds.

Hardness- They are very hard.

Reactivity - Generally ionic compounds are very reactive.

Non-Molecular Form- Ionic compounds do not exist in the forms of molecules. Their formula only indicates the number of atoms present in the compound.

Covalent Bond- A covalent bond is the chemical bond that involves the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding. For many molecules, the sharing of electrons allows each atom to attain the equivalent of a full outer shell, corresponding to a stable electronic configuration.

Example of Covalent Bond- Formation of a molecule of Methane, Chemical Formula CH4

Properties of Covalent Compounds

Molecular Form - Covalent compound exists as a separate molecules because they are formed by neutral atoms (they are electrically neutral) and the forces of attraction between these molecules is small.
State- Due to weak intermolecular forces, generally covalent molecules or covalent compounds are liquids and gases. However, some covalent substances are solids like iodine.

•    Liquid (H2O, HCl, Br2)
•    Gas (CO2, H2, Cl2,NH3)

Volatility- They are volatile.
Melting Point, Boiling Point (Thermal Stability) - Generally they have low M.P and B.P.
Solubility In Water- Covalent compounds are generally insoluble in water.
Solubility In The Organic Compounds- Covalent compounds are non-electrolyte because they do not conduct electricity.
Electrical Conductivity- Non-polar covalent compounds do not conduct electricity.
And polar covalent compounds conduct small amount of electricity.

Coordinate Bond also Called Dative Bond - The type of chemical bond in which one atom provides shared pair of electron for bond formation is called "Coordinate Covalent Bond".

Symbol: Dative bond is represented by an arrow (®), pointing from donor atom to the acceptor.

Examples -

Sigma Bond - In chemistry, sigma bonds (σ bonds) are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbital.

Pi Bond- In chemistry, pi bonds (π bonds) are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital. These orbital shares a nodal plane which passes through both of the involved nuclei.

Bond Energy - Bond energy (E) is the measure of bond strength in a chemical bond. It is the heat required to break one Mole (unit) of molecules into their individual atoms. For example, the carbon-hydrogen bond energy in methane E(C–H) is the enthalpy change involved with breaking up one molecule of methane into a carbon atom and 4 hydrogen radicals divided by 4.

Hydrogen Bond - A form of association between an electronegative atom and a hydrogen atom attached to a second, relatively electronegative atom. It is best considered as an electrostatic interaction, heightened by the small size of hydrogen, which permits proximity of the interacting dipoles or charges. Both electronegative atoms are usually (but not necessarily) from the first row of the Periodic Table, i.e. N, O or F. Hydrogen bonds may be inter-molecular or intramolecular. With a few exceptions, usually involving fluorine, the associated energies are less than 20 - 25 kJ mol −1 (5 - 6 kcal mol −1). This definition of Hydrogen is according to IUPAC Gold Book.

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