Class 9th Chemistry Chapter 4 Notes

Important Notes of Class 9th Chemistry Chapter 4 Notes Urdu Medium written by Honorable Sir M. Shahid Suib. These notes are very helpful in the preparation of Structure of Molecules Class 9 Notes for students of the Class 9th Chemistry Chapter 4 Notes Urdu Medium and these are according to the paper patterns of all Punjab boards.

Summary and Contents:
Topics which are discussed in the notes are given below:
  • Here are the detailed Ch 4 Chemistry Class 9 Notes to help you prepare for your exams.
  • Complete Exercise MCQs of Chapter No.4 Structure of Molecules in Urdu Medium.
  • Complete Exercise Short Questions with Answers of Chapter No.4 Structure of Molecules in Urdu Medium.
  • WHY DO ATOMS FORM CHEMICAL BONDS? It is a universal rule that everything in this world tends to become more stable. Atoms achieve stability by attaining electronic configuration of noble gases (He, Ne or Ar, etc) i.e. ns np. Having 2 or 8 electrons in the valence shell is sign of stability. Attaining two electrons in the valence shell is called duplet rule while attaining eight electrons in the valence shell is called octet rule.
  • The noble gases do have 2 or 8 electrons in their valence shells. It means all the noble gases have their valence shells completely filled. Their atoms do not have vacant space in their valence shell to accommodate extra electrons. Therefore, noble gases do not gain, lose or share electrons. That is why they are non-reactive.
  • CHEMICAL BOND: A chemical bond is defined as a force of attraction between atoms that holds them together in a substance. In other words, during bond formation there is some force which holds the atoms together.
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  • This attaining of 8 electrons configuration in the outermost shell either by sharing, by losing or by gaining electrons, is called octet rule. This octet rule only symbolizes that noble gas electronic configuration should be attained by atoms when they combine or react. 
  • TYPES OF CHEMICAL BOND: The valence electrons, which are involved in chemical bonding, are termed as bonding electrons. They usually reside in the incomplete or partially filled outermost shell of an atom. Depending upon the way how these valence electrons are involved in bonding, they result in following four types of chemical bonds:
  • Ionic Bond, Covalent Bond, Dative Covalent or Coordinate Covalent Bond, Metallic Bond and Ionic Bond:
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  • The elements of Group-1 and Group-2 being metals have the tendency to lose their valence electrons forming positively charged ions. Whereas non-metals of Group- 15 to Group-17 have the tendency to gain or accept electrons. They are electronegative elements with high electron affinities. If atoms belonging to these two different groups, metals and non-metals, are allowed to react, chemical bond is formed. This type of chemical bond, which is formed due to complete transfer of electron from one atom to another atom, is called ionic bond.
  • Covalent Bond: The elements of Group-13 to Group-17 when allowed to react with each other, they form a chemical bond by mutual sharing of their valence shell electrons. This type of bond, which is formed due to mutual sharing of electrons, is called a covalent bond.
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  • Types of covalent bonds: As described above, the covalent bond is formed by mutual sharing of electrons between two atoms. The electrons that pair up to form a chemical bond are called 'bond pair' electrons. Depending upon the number of bond pairs, covalent bond is classified into following three types:
  • Single Covalent bond: When one electron is contributed by each bonded atom, one bond pair is formed and it forms a single covalent bond. 
  • Polar and Non-polar Covalent Bond: If a covalent bond is formed between two similar atoms (homo-atoms), the shared pair of electrons is attracted by both the atoms equally. Such type of bond is called non-polar covalent bond. 
  • These bonds are formed by equal sharing of electron pair between the two bonding atoms. This type of bond is called a pure covalent bond. For example, bond formation in H2, and CI2.
  • Metallic Bond: The metallic bond is defined as a bond formed between metal atoms (positively charged ions) due to mobile or free electrons. The different properties shown by metals such as high melting and boiling points, good conductions of heat and electricity, hard and heavy nature, suggest existence of different type of chemical bond between atoms of metals.
  • Important MCQs and Questions of Structure of Molecules:

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