Q16 of 216 Page 473

i. In the formation of compound between two atoms A and B, A loses two electrons and B grains one electron.

A. What is the nature of bond between A and B?


B. Suggest the formula of the compound formed between A and B.


ii. On similar lines explain the formation of MgCl2 molecule.


iii. Common salt conducts electricity only in the molten state. Why?


iv. Why is melting point of NaCl high?

i. A) The nature of bond between A and B will be ionic, as transfer of electrons is taking place forming an ionic compound.


(Ionic bond is a bond formed between two dissimilar atoms that have a large electronegativity value difference in between them. One atom loses electrons while another atom gains electrons to acquire a stable electronic configuration. )


B) The formula of the compound formed between A and B is AB2. (A loses electrons while B gains one electron)


ii) Magnesium chloride or MgCl2 is an ionic compound. Ionic compounds are formed due to the electrostatic force of attraction between oppositely charged ions. Magnesium chloride is made of Mg2+ and Cl- ions. One atom of magnesium has 12 electrons so when it loses two electrons, the number of electron sin the outermost shell is 8 electrons. Similarly, an atom of chlorine has 17 electrons so when it gains one electron, the number of electrons in the outermost shell now is 8. (Magnesium forms cation with charge +2 while Chlorine forms anion with charge -1) So therefore two chlorine anions form an ionic bond with one magnesium cation to form MgCl2.


iii) Common salt conducts electricity only in the molten state because for conduction of electricity, charged ions must be present in free state so that they can move about freely conducting the electricity. In ionic compounds like common salt or sodium chloride, the ions are not free but are ionic bonded in a crystal lattice hence cannot conduct electricity. However when they are in a molten state, ionic compounds (here NaCl) dissociates into Na+ and Cl-, these ions have mobility and are charge carriers and therefore common salt in the molten state can conduct electricity.


iv) Sodium combines with chlorine forming sodium chloride by ionic bond. This leads to a crystal lattice with a regular arrangement of ions held by strong forces. There is a strong electrostatic attractions between the positive and negative ions hence a lot of energy is required to overcome them hence the melting point is high.


More from this chapter

All 216 →
14

Three 2Ω resistors A, B and C are connected as shown in figure. Each of them dissipates energy and can with stand a maximum power of 18 W without melting. Find the maximum current that can flow through the three resistors.


OR


Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 2Ω in series with a combination of two resistors (4Ωeach) in parallel and a voltmeter across the parallel combination. Will the potential difference across the 2Ωresistor be same as that across the parallel combination of 4Ω resistors? Give reason.

 15

The given magnet is divided into three parts A, B and C.


Name the parts where the strength of the magnetic field is:


i. maximum


ii. minimum


How will density of magnetic field lines differs at these parts?

 17

Elements forming ionic compounds attain noble gas configuration by either gaining or losing electrons from their outermost shells. Give reason to explain why carbon cannot attain noble gas configuration in this manner to form its compounds. Name the type of bonds formed in ionic compounds and in the compounds formed by carbon. Also give reason why carbon compounds are generally poor conductors of electricity.

OR


i. State the meaning of functional group in a carbon compound. Write the functional group present in (a) ethanol and (b) ethanoic acid and also draw their structures.


ii. Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an additional reaction to occur write the chemical equation giving the name of the reactant and the product of such a reaction.

 18

i. Name the part of brain which controls

A. voluntary action,


B. involuntary action.


ii. What is the significance of the peripheral nervous system? Name the components of this nervous system and distinguish between the origin of the two.


iii. A. Identify the glands that secrete


• Insulin


• Thyroxin


B. Explain with an example how the timing and amount of hormone secreted are regulated in human body.