OCTET RULE- During a chemical reaction the atoms tend to adjust their electronic arrangement in such a way that they achieve 8 e - in their outermost electron . This is called octet rule .
CHEMICAL BOND- the chemical force which keeps the atoms in any molecule together is called a chemical bond .
IONIC BOND- The columbic force of attraction which holds the appositively charged ions together is called an ionic bond . An ionic bond is formed by the complete transfer of one or more electrons from the atom of a metal to an atom of non- metal .
LATTICE ENTHALPY- The molar enthalpy change accompanying the complete separation of the constituent particles that compose of the solids ( such as ions for ionic solid , molecules for molecular solids ) under standard conditions is called lattice enthalpy ( ∆lH o ). The lattice enthalpy is a positive quantity .
ELECTRO VALENCY : The number of electrons lost or gain by an atom of an element is called as electrovalency .
The element which give up electrons to form positive ions are said to have positive valency , while the elements which accept electrons to form negative ions are said to have negative valency .
FORMATION OF AN IONIC BOND : It is favoured by , ( i ) the low ionisation enthalpy of a metallic element which forms the cations , ( ii ) High electron gain enthalpy of non- metallic element which forms the anions , ( iii ) Large lattice enthalpy i . e ; the smaller size and the higher charge of the atoms .
COVALENCY : The number of electrons which an atom contributes towards mutual sharing during the formation of a chemical bond called its covalency in that compound .
SINGLE COVALENT BOND : A covalent bond formed by the mutual sharing of one pair of electrons is called a single covalent bond , or simply a single bond . A single covalent bond is represented by a small line ( − ) between the two atoms .
DOUBLE COVALENT BOND : A covalent bond formed by the mutual sharing of two pair of electrons is called a double covalent bond , or simply a double bond . A double covalent bond is represented by two small horizontal lines (=) between the two atoms . E . g . O = O , O = C = O etc .