Question

Which ionic compound is expected to form from combining the following pairs of elements? (a) barium and fluorine, (b) cesium and chlorine, (c) lithium and nitrogen, (d) aluminum and oxygen.

Short answer

The ionic compounds formed from the given pairs of elements are: (a) \(BaF_2\), (b) \(CsCl\), (c) \(Li_3N\), and (d) \(Al_2O_3\).

Step-by-step solution

(a) Barium and Fluorine

Step 1: Identify charges of ions - Barium (Ba) is in group 2 of the periodic table, so it forms a \(+2\) ion: \(Ba^{2+}\). - Fluorine (F) is in group 17 (group 7 in terms of valence electrons), so it forms a \(-1\) ion: \(F^-\). Step 2: Combine ions to form a neutral compound - As the charge of Ba is \(+2\) and the charge of F is \(-1\), we need to combine them in a way that results in a neutral compound, i.e., 1 Ba ion and 2 F ions: \(BaF_2\).

(b) Cesium and Chlorine

Step 1: Identify charges of ions - Cesium (Cs) is in group 1 of the periodic table, so it forms a \(+1\) ion: \(Cs^+\). - Chlorine (Cl) is in group 17 (group 7 in terms of valence electrons), so it forms a \(-1\) ion: \(Cl^-\). Step 2: Combine ions to form a neutral compound - As the charge of Cs is \(+1\) and the charge of Cl is \(-1\), we need to combine them in a way that results in a neutral compound, i.e., 1 Cs ion and 1 Cl ion: \(CsCl\).

(c) Lithium and Nitrogen

Step 1: Identify charges of ions - Lithium (Li) is in group 1 of the periodic table, so it forms a \(+1\) ion: \(Li^+\). - Nitrogen (N) is in group 15 (group 5 in terms of valence electrons), so it forms a \(-3\) ion: \(N^{3-}\). Step 2: Combine ions to form a neutral compound - As the charge of Li is \(+1\) and the charge of N is \(-3\), we need to combine them in a way that results in a neutral compound, i.e., 3 Li ions and 1 N ion: \(Li_3N\).

(d) Aluminum and Oxygen

Step 1: Identify charges of ions - Aluminum (Al) is in group 13 (group 3 in terms of valence electrons), so it forms a \(+3\) ion: \(Al^{3+}\). - Oxygen (O) is in group 16 (group 6 in terms of valence electrons), so it forms a \(-2\) ion: \(O^{2-}\). Step 2: Combine ions to form a neutral compound - As the charge of Al is \(+3\) and the charge of O is \(-2\), we need to combine them in a way that results in a neutral compound, i.e., 2 Al ions and 3 O ions: \(Al_2O_3\).

Key concepts

Chemical Bonding

Chemical bonding is the process by which atoms combine together to form compounds. It's like a glue that holds the atoms together. One of the primary types of chemical bonds is the ionic bond. In ionic bonding, atoms transfer electrons to achieve stability. This usually happens between metals and non-metals. Metals tend to lose electrons and become positively charged ions, while non-metals tend to gain electrons and become negatively charged ions.

In the context of our exercise, barium and fluorine combine through ionic bonding. Barium, a metal, loses two electrons, and fluorine, a non-metal, gains one electron per atom. As a result, they form the ionic compound barium fluoride, or \(BaF_2\).

Ionic compounds are typically formed between elements that are far apart from each other on the periodic table, indicating a high difference in electronegativity.

Ionic Charges

Understanding the charges on ions is crucial to predicting the formulas of ionic compounds. Each element can form ions by gaining or losing electrons, leading to an electric charge. The charge of an ion is denoted by a superscript: for example, \(Na^+\) means a sodium ion has lost one electron.

In our examples, cesium forms a positively charged ion \(Cs^+\) by losing one electron, and chlorine forms a negatively charged ion \(Cl^-\) by gaining one electron. Combining them produces \(CsCl\), which is a compound with no net electric charge.

When forming ionic compounds, the total positive and negative charges must balance out. This is the basis for determining the ratios in which ions combine.

Neutral Compounds

A compound is neutral when the total positive charge equals the total negative charge. To form a neutral ionic compound, you determine how many of each type of ion is needed to balance out the charges.

In our example with lithium and nitrogen, lithium forms a \(+1\) charged ion \(Li^+\), and nitrogen forms a \(-3\) charged ion \(N^{3-}\). It takes three \(Li^+\) ions to balance the charge of one \(N^{3-}\) ion, resulting in the compound \(Li_3N\).

This balancing of charges ensures that the ionic compound does not have any leftover charge, aligning with the principle of electroneutrality. Each positive charge needs a matching negative charge, which leads to a stable ionic compound.

Periodic Table Groups

The periodic table helps us predict the charge of ions based on an element's group. Groups are the vertical columns on the periodic table, and elements within the same group often exhibit similar chemical behaviors.

For example:

• Elements in Group 1, like cesium and lithium, typically form \(+1\) ions.
• Elements in Group 2, such as barium, form \(+2\) ions.
• Elements in Group 13, like aluminum, form \(+3\) ions.
• Elements in Group 15, like nitrogen, form \(-3\) ions.
• Group 16 elements, such as oxygen, form \(-2\) ions.
• Group 17 elements, such as fluorine and chlorine, form \(-1\) ions.

Identifying these charges enables the prediction and formulation of ionic compounds accurately. Understanding periodic table trends makes it easier to deduce how elements will interact with each other in terms of ion formation.