10th Class Science Metals and Non-metals Question Bank 10th CBSE Science Metals and Non-metals

  • question_answer     (i) Write the electron-dot structures for sodium, oxygen and magnesium. (ii) Show the formation of Na2O and MgO by the transfer of electrons. What are the ions present in these compounds?

    Answer:

                        (i)

    Metal Symbol Atomic number Electronic configuration K, L, M, N No. of outermost electrons Electron dot structures
    Sodium Na 11 2, 8, 1 1 Na.
    Oxygen O 8 2, 6 6
    Magnesium Mg 12 2, 8, 2 2
      (ii) Formation of Na2O: The atomic number of sodium is 11 and it has only one valence electron. Hence, electronic configuration of 11Na is 2, 8, 1. The atomic number of oxygen is 8 and it has 6 electrons in its valence shell. Hence, electronic configuration of 8O is 2, 6. Sodium has a tendency to lose the valence electron and oxygen has a tendency to gain the electron lost by sodium. Since, sodium can lose only one electron of the valence shell and oxygen atom needs two electrons to complete its octet in the valence shell, two atoms of sodium combine with one atom of oxygen. By losing valence electron, sodium is changed into Na+ and by gaining two electrons lost by two sodium atoms, oxygen atom is changed into an oxide anion, O2-. In this process, both the atoms, sodium and oxygen, obtain the stable electronic configuration of the noble gas neon. The oppositely charged sodium ion, Na+ and oxide ion, O2- are now held together by electrostatic force of attraction or by ionic or electrovalent bond. Na2O is, therefore, an ionic or electrovalent compound. Formation of MgO: The atomic number of magnesium =12 Its electronic configuration is K, L, M.                         2, 8,  2 It has two electrons in its outermost shell. So, the magnesium atom donates its 2 valence electrons and forms a stable magnesium ion, Mg2+ to attain the electronic arrangement of neon atom. Mg ® Mg2+ + 2e- 2, 8, 2       2, 8 The atomic number of oxygen = 8 Electronic configuration = K, L                                 2,   6 It has 6 electrons in its valence shell. Therefore, it requires 2 more electrons to attain the stable electronic arrangement of neon gas. Thus, oxygen accepts 2 electrons donated by magnesium atom and forms a stable oxide ion, O2-   O + 2e- ® O2-  2, 6                  2, 8 The oppositely charged magnesium ions, Mg2+, and oxide ions, O2- are held together by a strong force of electrostatic attraction to form magnesium oxide compound Mg 2 +O2- or  MgO.                 MgO is an ionic compound. (iii) The ions present in Na2O are sodium ions (2Na+) and oxide ion O2-. The ions present in MgO are magnesium ion (Mg 2 +) and oxide ion O2- .


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