9th Science Guide Unit 13 Chemical bonding

9th Std Science Lesson 13 Chemical bonding – English Medium Guide

9th Science Book Back Answers Unit 13. 9th Science Lesson 13 Universe Book Back Answers. 9th Standard Science Samacheer kalvi Guide Book Back Answers download PDF Tamil Medium and English Medium book in answers. 9th All Subject Guide. Class 9 Science Questions and Answers. Class 1 to 12 All Subject Guide.  

9th Science Guide Unit 13 Chemical bonding

I. Choose the correct answer:

1. Number of valence electrons in carbon is

1. 2
2. 4
3. 3
4. 5

Ans : 4

2. Sodium having atomic number 11, ready to ___________________ electron/electrons to attain the nearest Noble gas electronic configuration.

1. gain one
2. gain two
3. lose one
4. lose two

Ans : lose one

3. Atoms having 1,2 or 3 electrons in its valence shell will readily form ________

1. cation
2. anion

Ans : cation

4. The element that would form anion by gaining electrons in a chemical reaction is _______________

1. a) Potassium
2. b) Calcium
3. c) Fluorine
4. d) Iron

Ans : Fluorine

5. Bond formed between a metal and non metal atom is usually __________

1. ionic bond
2. covalent bond
3. coordinate bond

Ans : ionic bond

6. ______________ compounds have high melting and boiling points.

1. Covalent
2. Coordinate
3. Ionic

Ans : Ionic

7. Covalent bond is formed by __________

1. transfer of electrons
2. sharing of electrons
3. sharing a pair of electrons

Ans : sharing of electrons

8. Oxidising agents are also called as ___________ because they remove electrons form other substances.

1. electron donors
2. electron acceptors

Ans : electron acceptors

9. Elements with stable electronic configurations have eight electrons in their valence shell. They are ___

1. Halogens
2. Metals
3. Noble gases
4. non metals

Ans : Noble gases

II. Answer in brief

1. How do atoms attain Noble gas electronic configuration.

Atoms can combine either by transfer of valence electrons from one atom to another or by sharing of valence electrons in order to achieve the stable outer shell of eight electrons

2. CCl4 is insoluble in water but NaCl is soluble in water. Give reason.

CCl4 is a Covalent compound but NaCl is a Ionic Compound.

Water is a polar solvent so NaCl is soluble in water.

CCl4 is soluble in non polar solvent.

3. Explain Octet rule with an example.

The octet rule is a chemical rule of thumb that reflects observation that atom of maingroup elements tend to combine in such a way that each atom has eight electrons in its valance shell, giving it the same electron configuration as a noble gas.

4. Write a note on different types on bonds?

• Ionic bonds
• Covalent bonds
• Co-Ordinate Covalent bond.

5. Find the odd one out.

1. H₂, Cl₂, NaCl, O₂, N₂

NaCl

1. H₂O₂, MnO₄–, LiAlH4, Cr₂O₂^2–

LiAlH4

6. Correct the wrong statements.

1. Ionic compounds dissolve in non polar solvents

Ionic compounds dissolve in polar solvents

1. Covalent compounds conduct electricity in molten or solution state.

Covalent compounds do not conduct electricity in molten or solution state.

7. Complete the table give below.

Element	Atomic number	Electron distribution	Valence electrons	Lewis dot structure
Lithium	3	2,1	1
Boron	5	2,3	3
Oxygen	8	2,6	6

 

8. Draw the electron distribution diagram for the formation of Carbon di oxide (CO2) molecule.

9. Fill in the following table according to the type of bonds formed in the given molecule.

CaCl₂, H₂O, CaO, CO, KBr, HCl, CCl₄, HF, CO₂, Al₂Cl₆

 

Ionic bond	Covalent bond	Coordinate covalent bond
CaCl2	H2O, CCl4	CO
CaO, KBr	HF, CO2	…………
HCl	Al2Cl6	………….

10. Choose the correct answer form the choices given below.

Te property which is characteristics of an Ionic compound is that

1. it ofen exists as gas at room temperature
2. it is hard and brittle
3. it undergoes molecular reactions
4. it has low melting point

Ans : it is hard and brittle

11. Identify the following reactions as oxidation or reduction

1. Na → Na⁺ + e^–

Ans : Oxidation reactions

1. Fe³+ + 2e^– → Fe⁺

Ans : Reduction reactions

12. Identify the compounds as Ionic/Covalent/Coordinate based on the given characteristics.

1. Soluble in non polar solvents –

Ans : Covalent bond

1. undergoes faster/instantaneous reactions –

Ans : Ionic bond

1. Non conductors of electricity –

Ans : Covalent bond

1. Solids at room temperature –

Ans : Co-ordinate Covalent bond

13. Considering MgCl2 as ionic compound and CH4 as covalent compound give any two diferences between these two compounds.

Ionic Bond	Covalent Bond
1. Transfer of electron	Sharing of electron
2. It is solid at room Temperature	It is gas, liqiud and softness at room Temperature

14. Why are Noble gases inert in nature?

All noble gases have incomplete valance shell, and tends to stable electronic configuration. so Noble gas inert in nature.

9th Science Guide Unit 13 Chemical bonding

III. Answer in detail

1. List down the diferences between Ionic and Covalent compounds.

Ionic Compounds	Covalent Compounds
Formed by the transfer of electrons from a metal to a non-metal atom	Formed by sharing of electrons between non metal atoms
Strong electrostatic force of attraction between cations and anions	Mutual sharing of electrons and so weak force of attraction between atoms
Solids at room temperature	Gases, liquids and soft solids
Conducts electricity in molten state or in solutions	Non-conductors of electricity
Have high melting and boiling points	Have low melting and boiling points
Soluble in polar solvents	Soluble in non-polar solvents
Hard and brittle	Soft and waxy
Undergo ionic reaction which are fast and instantaneous	Undergo molecular reactions which are slow

2. Give an example for each of the following statements.

1. a compound in which two Covalent bonds are formed

O²  O = O

1. a compound in which one ionic bond is formed

HCl

1. a compound in which two Covalent and one Coordinate bonds are formed

CO

1. a compound in which three covalent bonds are formed

N = N

1. a compound in which Coordinate bond is formed

NH⁴+

3. Identify the incorrect statement and correct them.

1. Like covalent compounds, Coordinate compounds also contain charged particles (ions), so they are good conductors of electricity.

Like covalent compounds, Coordinate compounds also contain charged particles (ions), so they are bad conductors of electricity.

1. Ionic bond is a weak bond when compared to Hydrogen bond

Ionic bond is a strong bond when compared to Hydrogen bond.

1. Ionic or electrovalent bonds are formed by mutual sharing of electrons between atoms.

Ionic or electrovalent bonds are formed by mutual transfer of electrons between atoms.

1. Loss of electrons is called Oxidation and Gain of electron is called Reduction.
2. Loss of electrons is called Oxidation and Gain of electron is called Reduction. (statement Correct)
3. Te electrons which are not involved in bonding are called valence electrons.

The electrons which are not involved in bonding are called lone pair electrons.

4. Discuss in brief about the properties of Coordinate covalent compounds.

Characteristics of coordinate covalent compounds

Te compounds containing coordinate covalent bonds are called coordinate compounds.

1. Physical state

These compounds exist as gases, liquids or solids.

1. Electrical conductivity

Like covalent compounds, coordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.

1. Melting point

These compounds have melting and boiling points higher than those of purely covalent compounds but lower than those of purely Ionic compounds.

1. Solubility

Insoluble in polar solvents like water but are soluble in non-polar solvents like benzene, CCl4, and toluene.

 

1. Reactions

Coordinate covalent compounds undergo molecular reactions which are slow.

5. Find the oxidation number of the elements in the following compounds.

1. C in CO2

x + 2(-2)	= 0
x – 4	= 0
x	= 4
C = + 4

1. Mn in MnSO⁴

x + 1(6) + 4(-2)	= 0
x + 6 – 8	= 0
x – 2	= 0
x	= 2
Mn = + 2

1. N in HNO₃

1(1) + x + 3(-2)	= 0
1 + x + 6	= 0
x – 5	= 0
x	= 5
N = + 5