Chemical Bonding Book Back Questions 9th Science Lesson 13
9th Science Lesson 13
13] Chemical Bonding
Book Back Questions with Answer and Do You Know Box Content
Do You Know?
The number of electrons lost from a metal atom is the valency of the metal and the number of electrons gained by a non-metal is the valency of the non-metal.
Note that dots are placed one to each side of the letter symbol until all four sides are occupied. Then the dots are written two to a side until all valence electrons are accounted for. The exact placement of the single dots is immaterial.
The number of electrons that an atom of an element loses or gains to form an electrovalent bond is called its Electrovalency.
Covalent bonds are of three types:
1. Single covalent bond represented by a line (-) between the two atoms. Eg. H – H
2. Double covalent bond represented by a double line (=) between the two atoms. Eg. O = O
3. Triple covalent bond represented by a triple line (=) between the two atoms. Eg. N = N
Polar solvents contain bonds between atoms with very different electro-negatives, such as oxygen and hydrogen. Ionic compounds are soluble in polar solvents. Ex: water, ethanol, acetic acid, ammonia.
Non polar solvents contain bonds between atoms with similar electro negativities, such as carbon and hydrogen. Covalent compounds are soluble in non-polar solvents. Ex: acetone, benzene, toluene, turpentine.
Electro-negativity is the tendency of an atom in a molecule to attract towards itself the shared pair of electrons.
Choose the best answers:
1. Number of valence electrons in carbon is
(a) 2
(b) 4
(c) 3
(d) 5
2. Sodium having atomic number 11, is ready to ____________ electron/electrons to attain the nearest noble gas electronic configuration.
(a) Gain one
(b) Gain two
(c) Lose one
(d) Lose two
3. The element that would form anion by gaining electrons in a chemical reaction is _______________
(a) Potassium
(b) Calcium
(c) Fluorine
(d) Iron
4. Bond formed between a metal and non-metal atom is usually ____________
(a) Ionic bond
(b) Covalent bond
(c) Coordinate bond
5. ______________ compounds have high melting and boiling points.
(a) Covalent
(b) Coordinate
(c) Ionic
6. Covalent bond is formed by ______________
(a) Transfer of electrons
(b) Sharing of electrons
(c) Sharing a pair of electrons
7. Oxidising agents are also called as _______________ because they remove electrons from other substance.
(a) Electron donors
(b) Electron acceptors
8. Elements with stable electronic configurations have eight electrons in their valence shell. They are __________
(a) Halogens
(b) Metals
(c) Noble gases
(d) Non metals
9. The property which is characteristics of an Ionic compound is that
(a) It often exists as gas at room temperature
(b) It is hard and brittle
(c) It undergoes molecular reaction
(d) It has low melting point
10. Identify the following reactions as oxidation or reduction
(a) Na 🡪 Na+ + e–
(b) Fe3+ + 2 e– 🡪 Fe+
11. Identify the compounds as Ionic/Covalent/Coordinate based on the given characteristics:
(a) Soluble in non polar solvents
(b) Undergoes faster/instantaneous reactions
(c) Non conductors of electricity
(d) Solids at room temperature
Answers:
Choose the best answers:
1. 4 2. Lose one 3. Fluorine 4. Ionic bond 5. ionic 6. sharing of electrons
7. electron acceptors 8. noble gases 9. it is hard and brittle. 10. Na → Na+ + e–
11. a) Covalent compounds b) Ionic compounds c) Covalent compounds d) Ionic compounds