Tuesday, 16 July 2019

9th class Chemistry Notes Chapter 4 - MCQs,Questions and Practicals pdf

Matric 9th Chemistry Notes Chapter 4 - MCQs,Questions and Practicals
Here are the Matric 9th Chemistry Notes Chapter 4 Structure of Molecules - MCQs,Questions and Practicals. It Includes short questions, Long question and Practical Questions pdf download or view online
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What is duplet rule?
 Ans. Duplet Rule: "Attaining 2 electrons in the Valence shell is called duplet rule Example: Helium (He) has two electrons in its valence shell. Its electronic configuration s 1s. Thus, obeys duplet rule.
(i) What is meant by a chemical force /chemical bond? Give its types.
 Ans. Chemical Forces/Chemical Bond:The forces responsible for bonding the atoms together in a molecule are called chemical forces c chemical bonds."
 Types of Chemical Bonds: There are four main types of chemical bonds. These are as following: 
(1) Ionic Bond 
(2) Covalent Bond
 (3) Coordinate/Dative Covalent Bond 
(4) Metallic Bond
 (iv) When does a chemical bond is formed between two atoms and when it does not?
 Ans. When two approaching atoms come closer, the attractive as well as repulsive forces become operative. The formation of chemical bond is a result of net attractive forces which dominate. The energy of that system is lowered and molecule is formed. Otherwise if repulsive forces become dorninate no chemical bond will be formed. In that case there will be increase in the energy of the system due to creation of repulsive forces
(vi) Give two/four properties of ionic compounds.
 Ans. Properties of Ionic Compounds: 
(1) ionic compounds are mostly crystalline solids
 (2) Ionic compounds in solid state havo negligible electrical conductance but they are good conductors in solution and in the molten form. It is due to presence of free lans in them.
 (3) Ionic compounds have high melting and boiling points. For example, sodium chloride has melting point 800 C and a boiling point 1413 C As ionic compounds are made up of positive and negative ions, there exist strong electrostatic forces of attraction between oppositely charged fons. So, a great amount of energy is required to break these forces They dissolve easily in polar solvents like water. Water has high dielectric constant that weakens the attraction between two bonded ons.
 Examples:
 NaCi, KCI, Nal, etc.
(v) How we can predict whether a chemical bond will be ionic or covalent in nature?
 (1) f the difference of electronegativities between two bonded atoms of different elements is more than 1.7, then the bond b/w the bonded atoms will be predominantly ionic bond.
 (2) If the difference of electronegativities between two atoms of different elements is less than 1.7, then the bond between two bonded atoms will be predominantly covalent.
 (ii) Give two/four properties of metals.
 Ans. Metals:
 Properties of Metals:
 Metals have common property of conducting heat and electricity. It gives them prime role in many technologies. Major properties shown by the metals are as following:
1) They show metallic luster.
2) They are usually malleable. Malleability is the property by virtue of which a metal can be drawn into sheets.
(3) Metals are ductile. Ductility is the property by virtue of which a metal can be drawn into wires
(4) They have usually high melting and Boiling points.
(5) Being greater in size, they have low ionization energies and form cations (M) very easily.
6) They are good conductors of heat and electricity in solid and liquid states due to mobile electrons.
 (iii) Differentiate between malleability and ductility of metals?
Ans. Malleability: "Malleability is the properties by virtue of which a metal can be drawn into sheets Ductility: Ductility is the property by virtue of which a metal can be drawn into wires.
 (v) Why does ice float on water?
 Ans. The important phenomenon of floating of ice over water is because of hydrogen bonding.
 The density of ice at 0°C (0.917g cm) is less than that of liquid water at 0°C (1.00g cm). In the quid state, water molecules move randomly. However, when water freezes, the molecules arrange themselves in an ordered form, that gives them open structure. This process expands the molecules, that result in ice being less dense as compared to water That is why ice float on water.
 (vi) What do you mean by induced dipole?
 Ans. 
Induced Dipole: A dipole which is produced artificially due to electrons distortion in a molecule by the other nearby dipole is called an induced dipole
 (OR)
 "A molecule in which polarity is created due to other polar molecule is called induced dipole 
Explanation: The positive end of the polar molecule attracts the mobile electron of the nearby non-polar molecule, and both molecules become dipoles. These forces are called dipole induced dipole forces.
 (viii) What is epoxy adhesive? Give its uses.
 Ans. Epoxy: Epoxy is a polymer that is formed from two different chemicals. These are referred as resin and the hardener. Epoxy adhesives are called structural adhesives.
 Uses of Epoxy Adhesive: Epoxy are high performance adhesives. They are used in the construction of aircraft, automobiles, bicycles, boats, golf clubs, where high strength bonds are required

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