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An unknown element, X, reacts with chlorine to form an ionic compound whose empirical...

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An unknown element, X, reacts with chlorine to form an ionic compound whose empirical formula is XCL_2. If the X has 18 electrons, identify the element. Show complete step by step solution to explain the process and answer.

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Posted (Answer #1)

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If element "X" has 18 electrons after the reaction has taken place, and the compound XCl2 represents a compound with an ionic bond, then the element is most likely calcium.  Calcium has an atomic number of 20, and is located on the periodic table of elements to the far left in group 2.  The elements in group 2 have 2 electrons in their outer electron orbital that they are willing to donate in chemical reactions with nonmetals.  Chlorine is in group 7A (or group 17, depending on which version of the periodic table you are using), which is also the halogen group.  The elements in this group have room for one electron in their outer electron shell.  So it would take two chlorine atoms to accept the two electrons available for ionic donation by calcium to form the compound calcium chloride, CaCl2.  Calcium 2 donated electrons, plus the 18 electrons mentioned in the problem, would equal 20.  The number of electrons is also equal to the number of protons in the nucleus, since there is a one to one ratio of protons to electrons.  So calcium should be the correct pick for element "X".


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Now Ionic compound/ bond is formed between metal and a non-metal, the bond is formed by losing and gaining of electron.

here the metal will lose electron forming cation (positive ions)and the non-metal will gain electron(forming negative ions)


Since X is a metal so it will loose electron. and it has 18 electron while forming the compound XCl2. Now 

2 Cl  + 2e =====> Cl-

a Cl atom can accept only one electron so 2 Cl menas 2 electron. These two electron are gained from X. So X has already lost 2 electron.

X  ===? X(2+)  +  2e


So the total number of electron in X would be (18+2) that is 20. 

so the element would be Calcium as calcium has 20 electron

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