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Question:  Potassium chloride is an electrovalent compound, while hydrogen chloride is a covalent compound. But, both conduct electricity in their aqueous solutions. Explain. Solution: A solution conducts electricity due to the presence of charged ions. Potassium chloride is an electrovalent compound so it contains ions and can conduct electricity. Hydrogen chloride is a covalent compound but it is polar in nature so it ionises in its aqueous solution and since ions are present in the solution, it can conduct electricity.

  Question: Taking MgCl 2 as an example of electrovalent bond, CCl 4 as a covalent bond, give a difference between electrovalent and covalent bonds. Solution: Electrovalent bond as in MgCl 2 Covalent bond as in CCl 4 It involves complete transfer of electrons. It involves sharing of electrons.

  Question: Elements X, Y and Z have atomic numbers 6, 9 and 12 respectively. State the type of bond between Y and Z and give its molecular formula. Solution: Electrovalent bond will be formed between Y and Z and its molecular formula will be ZY 2 . Explanation: Write the electronic configuration of the three elements.  X with atomic number 6- 2, 4 Y with atomic number 9- 2, 7 Z with atomic number 12- 2, 8, 2 Y will gain one electron, so its valency is 1 and Z will lose 2 electrons so its valency is 2. The atom which loses electrons is written first as in NaCl, MgCl 2   , so here Z will be written first. Applying criss-cross method,  Z     Y 2      1 1 will go to Z and 2 will go to Y So, the formula will be  ZY 2 .

  Question: Elements X, Y and Z have atomic numbers 6, 9 and 12 respectively. Which one:  (i) forms an anion  (ii) forms a cation Solution: (i)                       Y (ii)                     Z Explanation: Write the electronic configuration of the elements given. X (Atomic number-6) - 2,4 Y (Atomic number- 9) - 2,7 Z (Atomic number- 12) - 2, 8, 2 X can gain 4 electrons or lose 4 electrons. Y will accept 1 electron to have 8 electrons in its valence shell. Z will lose 2 electrons to attain octet(8 electrons) in the last shell. (i) Anion means negative ion. Since Y will gain electrons, it will become negatively charged and form an anion. (ii) Cation means positive ion. Since Z will lose electrons, it will become positively charged and form a cation.

 Question: If electrons are getting added to an element Y; then   (a) Is Y getting oxidised or reduced?  (b) what charge will Y migrate to during the process of electrolysis? Solution: (a) Y is getting reduced. (b) Y will migrate to positive charge during the process of electrolysis. Explanation: Loss of electrons is oxidation. Gain of electrons is reduction. (a) Since Y is gaining electrons, it is getting reduced. (b) Since Y is gaining electrons, it will become negatively charged. Opposite charges attract, so negatively charged Y will migrate to positive charge. 

  Question: Match the atomic numbers 4, 8, 10, 15 and 19 with each of the following: (a)          Element which can form trivalent ion (b)          An element with 4 shells. (c)           Element with 6 valence electrons. (d)          Element which does not form ion. Solution : (a)          15 (b)          19 (c)           8 (d)          10 Explanation: First, write their electronic configuration 4- 2, 2 8- 2, 6 10- 2, 8 15- 2, 8, 5 19- 2, 8, 8, 1 (a) Trivalent ion means it will have charge 3, which means that it will gain or lose 3 electrons. Element with atomic number 15 has 5 electrons in its valence shell, so it will gain 3 electrons to hav...

  Question: An element A has 1 electron in its first shell. It combines with element B having 7 electrons in its third shell. What type of bond is formed? Solution: Covalent bond Explanation: A has 1 electron in its first shell and so it needs 1 electron to attain the electronic configuration of Helium (2). B has 7 electrons in its third shell and so it needs 1 electron to have 8 electrons in its last shell. Since both of them need electrons, they will share electrons and so covalent bond will be formed.