9 Class- Chemical Bonding and Reactions

Chemical Bonding and Reactions

Chemical Bonding

Molecule forms by the combination of two atoms of elements. The attraction force operate between atoms is known as Chemical Bonding. Now we learn step by step about chemical bonding and reactions.

Chemical bonds are formed due to presence of valence electrons in atoms. Valence electrons present in the outermost shell of atom. These are chemical bonding notes by ChemistryNotesInfo website.

Why chemical bonds are formed between atoms?

Chemical bonds are formed between atoms to achieve stable state, like inert or noble gases.

Atoms achieve stable state of nearest inert gas with complete octet in two ways:

  • By exchanging electron with any other atom.
  • By sharing electron with any other atom.

Types of Chemical Bonds or Chemical Bonding

  • Electrovalent Bond or Ionic bond
  • Covalent Bond

Electrovalent Bond is also known as Ionic Bond. Because compound formed is ionic in nature, and also having polarity. In electrovalent bond, one atom loose electron to form positive ion called cation. And another atom, which gain electron to form negative ion called anion. This type of bond is known as Electrovalent Bond or Ionic Bond.

Example: NaCl        

Na                    ——–>          Na+ +e        

Cl  +  e            ——–>         Cl-        

Na+  +  Cl-       ——–>          NaCl

Electrovalent Compound

The compounds which contain ionic or electrovalent bonds, are known as Electrovalent or Ionic Compounds. Mainly electrovalent compounds are formed, due to reaction between highly electropositive and highly electronegative atoms.

Characteristics of Electrovalent Compounds

1. Crystal Structure:

                              In solid state of electrovalent compounds. Anions and cations are arranged in regular manner called as crystal. In which anions surrounded by definite number of cations. And cations surrounded by definite number of anions.

2. Physical Nature:

       Ionic or electrovalent compounds are generally hard. And their hardness increases with increasing ionic charge and decreasing distance between ions.

3. Solubility:

Positive ion of ionic compound, attach with negative part of polar solvent. And negative ion of ionic compound, attach with positive part of polar solvent. So ionic or electrovalent compounds are soluble in polar solvents like water. But insoluble in non polar solvents like benzene, ether, alcohol.

4. Melting Point and Boiling Point:

Electrovalent or ionic compounds, have high melting and boiling points. Because they need large amount of energy to break strong ionic bonds.

5. Electrical Conductivity:

In molten and solution forms, electrovalent compounds conduct electricity. Because ions flows in molten and solution forms.

Covalent Compound

Covalent bonds are the bonds. Which are formed due to the, equal sharing of electrons between two atoms.  These chemistry notes are provided by Chemistry Notes Info Organization www.ChemistryNotesInfo.com . This type of bonds (i.e. covalent bonds) is formed in atoms. Which carry four or more than four electrons in their outermost shell.

Generally sharing of electrons happen in two ways –

  • Equal Sharing – Covalent Bond
  • One Side Sharing – Coordinate Bond

Covalent Compounds

Compound which are formed as a result of covalent bonding. And containing covalent bonds, are known as Covalent Compounds. Example: Hydrogen, Chlorine, Oxygen, Water, Ethanol etc.

Types of Covalent Bonds

Covalent Bonds are of three types which are as follows-

  • Single Covalent Bonds
  • Double Covalent Bonds
  • Triple Covalent Bonds

Single Covalent Bonds

These are bonds which are formed due to sharing of single pair of electrons between two atoms. These bonds are called single covalent bond. It is represented by single line (-). Example: Formation of H2 molecule, Formation of Cl2 molecule.

i. Formation of Hydrogen (H2) molecule:

In the outermost shell of hydrogen atom, it have single electron. Which it share with another hydrogen atom, to acquire inert configuration of helium. So single bond is formed between these two hydrogen atoms. And this single covalent bond is represented by single line (-)

ii. Formation of Chlorine Molecule (Cl2) :

In the outermost shell of chlorine atom, it have seven electrons. So chlorine share its one valence electron with another chlorine atom, to form chlorine molecule by single covalent bond.

Double Covalent Bonds

Bonds which are formed due to sharing of double pair of electrons between two atoms are called double covalent bond. It is represented by double line (=). Example: Formation of O2 molecule.

i. Formation of Oxygen (O2) molecule:

In the outermost shell of oxygen atom, it have six electrons. It share its two valence electrons with another oxygen atom to form oxygen molecule by double covalent bond.

Triple Covalent Bonds

Bonds which are formed due to sharing of triple pair of electrons between two atoms are called triple covalent bond. It is represented by triple lines. Example: Formation of N2 molecule.

i. Formation of Nitrogen (N2) molecule:

In the outermost shell of nitrogen atom, it have five electrons. It share its three valence electrons with another nitrogen atom to form nitrogen molecule by triple covalent bond.

Characteristics of covalent compounds

1. Crystal Structure:

The Crystal structure of covalent compounds is formed from atoms or molecules.

Also Crystal of covalent compounds are divided in three parts as –

  • These are crystals of covalent compounds whose molecule are very small and these molecules are held together by vander waals forces. Example: Sulphur, Iodine.
  • These are crystals of covalent compounds whose molecule are very large due to combination of every atom with other atom by covalent bonds. Example:  Diamond, Silica.
  • These are crystals of covalent compounds whose have separate layers. Example: Graphite.

2. Physical Nature:

Due to weaker force of attraction between the molecules of the covalent compounds, maximum covalent compounds are gases or liquids. But some covalent compounds exist as solid like Urea, Sugar, Glucose, and Naphthalene.

3. Solubility:

Covalent compounds are not soluble in polar solvents like water. But Covalent compounds are soluble in non-polar solvent like alcohol, ether, carbon tetra chloride.

4. Melting Point and Boiling Point ( MP and BP) :

Melting and boiling points of covalent compounds are very low. Because very less energy is required to overcome the weak force of attraction between the neutral molecules in the covalent compound. But Diamond and Graphite are exception because they have very high melting and boiling points.

5. Conductivity:

Covalent compounds do not have ions so they do not conduct electricity but some polar covalent compounds conduct very less electricity.

Polar Covalent Bond

In the covalent compound if one is more electronegative than other atom. Then shared pair of electrons is attracted towards more electronegative atom. So it acquire or obtain some partial negative charge, which is represented by delta negative (d-). And other atom acquire some partial positive charge, which is represented by delta positive (d+). Therefore polar bond forms. Which is known as Polar covalent bond.

Example : Hydrogen Chloride Molecule. In HCl molecule, Chlorine is more electronegative than Hydrogen so chlorine acquires partial negative charge and hydrogen acquire partial positive charge.

Characteristics of Polar Covalent Compounds

  • Polar covalent compounds are approximately 80% covalent and 20% ionic so they so characteristics of both covalent and ionic (or electrovalent) compounds.
  • In solution forms, polar covalent compounds are good conductor of electricity. Example: HCl
  • As compared to pure non-polar covalent compounds and electrovalent compounds, the melting point and boiling point of polar covalent compound are higher.

Chemical Reactions

Chemical Reaction is the reaction in which two or more than two substances react to form a new substance is known as Chemical Reaction. The substances which react may be ion or compound of element.

Reaction: Reactant reacts with each other to give product.                Reactant   ——–>  Product

Example of general chemical reactions from daily life is rusting of iron, formation of curd from milk etc.

Chemical Formula

Chemical Formula is simple representation of any compound by writing together the numbers and symbols of constituting elements forming that compound. Example: H2O, CaCl2, AlCl3, Ca(OH)2

Chemical Formula for Ionic Compounds

As we know Ionic compound formed as a result of electron transfer between metal and non-metal atoms. When we have to write chemical formula for ionic compound then write metal atom symbol on left hand side and non-metal atom symbol on right hand side. Metal atom name remain same but ‘ide’ or ‘ate’ suffix is added to non-metal atom name.

Ionic compound formed by one metal atom and non-metal atoms.

Metal Atom

Non-Metal Atom

Name of Compound

Chemical Formula  of Compound

Name and Symbol

No.

Name and Symbol

No.

Calcium (Ca)

1

Oxygen (O)

1

Calcium Oxide

CaO

Magnesium (Mg)

1

Chlorine (Cl)

2

Magnesium Chloride

MgCl2

Aluminium (Al)

1

Chlorine (Cl)

3

Aluminium Chloride

AlCl3

Chemical Formula for Covalent Compounds

As we know covalent compound formed as a result of electron sharing and contains non-metal atoms. When we have to write chemical formula for covalent compound then relatively less electronegative non-metal atom symbol is written on left hand side and other witch is more electronegative is written  on right hand side. Name of non-metal atom which is written on left hand side is remain same but ‘ide’ suffix is added to non-metal atom name which is written on right hand side. 

Covalent compound formed by two non-metal atoms.

Low Electronegative Non-Metal Atom

High Electronegative Non-Metal Atom

Chemical Name of Compound

Chemical Formula  of Compound

Name and Symbol

No.

Name and Symbol

No.

Carbon (C)

1

Oxygen (O)

1

Carbon Mono Oxide

CO

Carbon (C)

1

Oxygen (O)

2

Carbon Di Oxide

CO2

Phosphorus (P)

1

Chlorine (Cl)

3

Phosphorus Tri Chloride

PCl3

Phosphorus (P)

1

Chlorine (Cl)

5

Phosphorus Penta Chloride

PCl5

Nitrogen (N)

2

Oxygen (O)

5

Nitrogen Penta Oxide

N2O5

Formation of Compound

We get chemical formula of molecule by writing valence of 1st atom in front of 2nd atom and valence of 2nd atom in front of 1statom.

Example: valence of carbon is 4 and oxygen is 2. Write 4 in front of O and 2 in front of C in subscripts as shown below. C2O4 as we see, both valences are multiple of two, so divide it by two to get CO2 formula. Similarly,           

Na++ CO3-2   —> Na2CO3          

Al+3 + SO4-2  —>  Al2(SO4)3          

Mg+2+ N-3    —> Mg3N2

Simple Chemical Reaction

Chemical reaction is represented by chemical equation in brief by taking help of symbol and formula of participating substances in reaction.

General Rule for writing Simple Chemical Reaction

  • Reactant are written on left hand side and if more than one reactant are present than write plus (+) sign between them.
  • Product are written on left hand side and if more than one product are present than write plus (+) sign between them.
  • Arrow sign is placed between reactants and products.
    • Example: Zn + H2SO4 ( Reactants) —–> ZnSO4 + H2 (Products)
  • To get more information from the reaction write temperature, pressure, catalyst name above or below arrow sign.
  • On the right side of the gaseous substances  sign and on the left side of heavy substances which precipitate  sign is placed.
  • Reactions which absorb heat are known as endothermic reactions and (+Q) heat sign is added on reactant side.
  • Reactions which produce heat are known as exothermic reactions and (+Q) heat sign is added on product side.
  • (Aq) is written for aqueous solution substances.

Balancing of Chemical Reactions

For balancing of chemical reaction the no. of atom on reactant side should be equal to no. of atom on product side, so that total mass of reactant is equal to total mass of product. You read these 9 class notes at www.ChemistryNotesInfo.com of ‘Chemistry Notes Info’ organization website.

H2 + O2   —–>  H2O   (Imbalance Equation)

2H2 + O2 —–>   2H2O   (Balance Equation)

Types of Chemical Reactions

Types of Chemical Reaction
Types of Chemical Reaction
  • Addition Reaction
  • Decomposition Reaction
  • Substitution Reaction
  • Oxidation and Reduction Reaction

1. Addition Reaction

Reactions in which two or more than two substances reacts together to produce a new compound is known as Addition Reaction.

Example:- 2Mg + O2 ——> 2MgO

2. Decomposition Reaction

Reactions in which one compound get break into two or more than two simple compounds by breaking of chemical bonds, these chemical bonds get broken by heat, light or electricity.

Example:- CaCO3 ——> CaO + CO2

3. Substitution Reaction

Reactions in which one element replaces another element to form a new compound is known as Substitution Reaction.

Example:- CuSO4 (Aq) + Zn (s) —–> ZnSO4 (Aq) + Cu (s)

4. Oxidation and Reduction Reaction

Oxidation and reduction reaction are described below on these two basis- Oxidation and Reduction Reaction based on oxygen and hydrogen-

  • Removal of hydrogen and addition of oxygen is known as oxidation reaction.
  • Removal of oxygen and addition of hydrogen is known as reduction reaction.

Oxidation and Reduction Reaction based on electron transfer-

  • Oxidation reactions are the reactions in which atom or ion looses electrons.
  • Reduction reactions are the reactions in which atom or ion gains electrons.

Oxidation and Reduction reactions occurs simultaneously because electron removed from one atom or radical is added to another atom or radical.

Learn more about class 9 science at below links

Chemical Bonding and Reactions
Chemical Bonding and Reactions

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