Question

Identify the group number in the periodic table of \(\mathrm{X}\), a representative element, in each of the following ionic compounds: a. \(\mathrm{XCl}_{3}\) b. \(\mathrm{Al}_{2} \mathrm{X}_{3}\) c. \(\mathrm{XCO}_{3}\)

Short answer

a. Group 13, b. Group 16, c. Group 2.

Step-by-step solution

Analyze \(\text{XCl}_3\)

In \(\text{XCl}_3\), Chlorine (Cl) is in group 17 and typically forms a \(-1\) ion. Since there are 3 Chlorine atoms, the total negative charge is \(-3\). Therefore, element X must have a \(+3\) charge to balance this. Elements in groups 13 typically form \(+3\) ions, so X is in group 13.

Analyze \(\text{Al}_2 \text{X}_3\)

Aluminum (Al) is in group 13 and forms \(+3\) ions. There are 2 Aluminum atoms, contributing a total charge of \(+6\). Therefore, the 3 X atoms must contribute \(-6\) charge, making each X ion \(-2\). Elements in group 16 typically form \(-2\) ions, so X is in group 16.

Analyze \(\text{XCO}_3\)

The carbonate ion \(\text{CO}_3^{2-}\) carries a \(-2\) charge. Therefore, element X must have a \(+2\) charge to balance this. Elements in group 2 typically form \(+2\) ions, so X is in group 2.

Key concepts

Ionic Compounds

Ionic compounds are formed when atoms lose or gain electrons. This exchange of electrons results in the formation of positively charged ions (cations) and negatively charged ions (anions). These oppositely charged ions attract each other, creating a strong bond known as an ionic bond.
For example, in the compound \(XCl_3\), chlorine (Cl) usually forms a \(-1\) ion. If there are three chlorines, they total \(-3\) charge. To balance this, element X must contribute a \(+3\) charge.
Ionic compounds generally display specific properties, such as high melting and boiling points, and they often dissolve in water to form conductive solutions.

Representative Elements

Representative elements are found in groups 1, 2, and 13-18 of the periodic table. These elements are characterized by their valence electrons, which determine their chemical properties and reactivity. The group number of a representative element can often be identified by looking at the number of valence electrons it has.
For instance, in the case of \(Al_2X_3\), aluminum (Al) is a representative element in group 13, known to form \(+3\) ions. Elements in group 16 like sulfur (S) typically form \(-2\) ions, indicating our mystery element X in this compound belongs to group 16.
Another example is \(XCO_3\), where the carbonate ion \((CO_3^{2-})\) carries a \(-2\) charge. Hence, element X must be in group 2 to provide a \(+2\) charge to balance the compound.

Chemical Charges

Chemical charges are critical in understanding the composition and formation of ionic compounds. Atoms seek to achieve a stable electronic configuration similar to noble gases. This stability is reached most often by losing or gaining electrons and forming ions.
For example, in \(\text{XCl}_3\), chlorine (Cl) gains one electron to form a \(-1\) charge. With three chlorine atoms, they collectively contribute \(-3\) charge. Therefore, the element X must have a \(+3\) charge to balance it out.
Similarly, in the compound \(Al_2X_3\), aluminum (Al) loses three electrons to form \(+3\) charged ions. If there are two aluminum atoms contributing a \(+6\) charge, then X must provide \(-6\) charge, making each X ion \(-2\). This indicates X is an element from group 16, which typically forms \(-2\) ions.
Finally, in \(XCO_3\), the carbonate ion \((CO_3^{2-})\) has a \(-2\) charge, meaning that X must have a \(+2\) charge to keep the compound neutral. Thus, X would be a group 2 element.