Question Video: Connecting the Group Number with the Subscript in an Ionic Formula Chemistry

Consider the equation: 2X + 3Cl₂ ⟶ X₂Cl₆. Which of the following groups could X be in? [A] Group 17 [B] Group 2 [C] Group 13 [D] Group 5

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Video Transcript

Consider the equation below: Two X plus three Cl2 react to form X2Cl6. Which of the following groups could X be in? (A) Group 17, (B) group two, (C) group 13, (D) group five.

Groups are the columns on the periodic table. Each group in the periodic table has a different valence. The valence tells us how many electrons are lost or gained by an atom when it reacts. If we can determine the valence of the mystery element X, we’ll be able to determine what group X is in.

The element chlorine is located in group 17 of the periodic table. Chlorine tends to gain one electron when it reacts. This forms the chloride ion, which has a charge of one minus. In the product of this reaction, there are six chloride ions. The six chlorine atoms that reacted each gained one electron. So there’s a total negative charge of six minus in the compound. However, all compounds are neutral, so they have an overall charge of zero. So the two X atoms must contribute a total of six positive charges.

If there is a total charge of six plus when there’s two X atoms, then each X atom must have a charge of three plus. So atoms of X tend to lose three electrons to form ions with a charge of three plus. We can see that elements in group 13 of the periodic table tend to lose three electrons. So which of the following groups could X be in? The answer is (C), group 13.

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