Chemical Bond and Types of bonds ionic bond or elctrovalent bond

CHEMICAL BONDING 

Definition: The attractive force present between the atoms that holds the atoms together as a molecule is known as “Chemical Bond”
·      1) Why do atoms combine to form a molecule?
·      2) Why do atoms combine in a fixed ratio?
·      3) How can the properties of compounds be understood in term of attractive forces?

CAUSE OF CHEMICAL COMBINATION

·      Tendency to acquire inert gas electronic configuration (ns2np6). Atoms of elements acquire eight electrons in their valence shell by involving in chemical combination is known as “Octet rule”
·      Tendency to acquire minimum energy
1) The atoms are unstable and possess high energy
2) During bond formation energy is released.
This energy is known as bond energy.
3) Bond formation between atoms leads to stability with lesser energy.

OCTET RULE

·      Noble gas elements, except He(1s2), contain 8 electrons in the valence shell. The stability of these elements is due to its octet configuration.
·      Other than Noble gas elements contain less than 8 electrons in the valence shell.
·      Elements try to get octet configuration by means of bond formation
·      Atoms try to get 8 electrons in valence shell either by transfer or sharing of electrons.

TYPES OF BONDS

·      The type of bond formed between atoms depends on the nature of elements. The chemical bonds are
1)Ionic bond or electrovalent bond
2)Covalent bond
3)Metallic bond
4)Hydrogen bond
5)Vanderwaal’s forces 

IONIC BOND OR ELECTROVALENT BOND 

Definition: The electrostatic force of attraction between oppositely charged ions formed by the transfer of electrons is called as “Ionic Bond”. Example: Na+cl-
·      Ionic bond is formed between the atoms of
a) if electro negativity difference is more than 1.73.
b) between a metal with low ionization energy and a non-metal with high electro negativity.
·      Ionic bond formation is explained in 3 steps
i) formation of cation (from metal atom)
ii) formation of anion (from non-metallic atom) and
iii) association of oppositely charged ions due to electrostatic attractive force.

Example: Sodium chloride (NaCl) formation:
·      Sodium metal combines with chlorine gas to form crystalline solid sodium chloride explained in 3 steps .
Electron configuration of sodium is 1s2 2s2 2p6 3s1
(i)It readily loses valency electron and gets the nearest noble gas configuration (2s2 2p6)
·      Positive sodium ion is formed



(ii) Electron configuration of chlorine is 1s2 2s2 2p6 3s2 3p5
·      It gains one electron from sodium to get nearest noble gas configuration (3s2 3p6)
·      Negative chloride ion is formed


  (iii) The oppositely charged Na+ and Cl- ions are held together by electrostatic force of attraction,the ionic bond is formed









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