Chapter 5: Periodic Classifications of Elements

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Periodic Classifications of Elements


Element X forms a chloride with the formula XCl2, which is solid with a high melting point. X would most likely to be in the same group of the periodic table as:

(a) Na

(b) Mg

(c) Al

(d) Si


The metal chloride contains metal cation and chloride anion. The chloride anion has -1 charge because chlorine needs one electron to complete its octet. XCl2 contains a metal ion that has +2 charge.

The atomic number of sodium is 11 and its electronic configuration is (2,8,1). This means that sodium loses one electron to complete its octet and hence, it has +1 charge. Similarly, magnesium has +2 charge because it loses two electrons to complete its octet.

The atomic number of aluminium and silicon is 13 and 14 respectively. So, the charge of aluminium is +3 while that of silicon is +4. This means that X will belong to the same group in which the magnesium belongs.

Therefore, the correct answer is (b) Mg.

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