Question

Which oxide is more basic, \(\mathrm{MgO}\) or \(\mathrm{BaO}\) ? Why?

Short answer

BaO is more basic than MgO due to its greater ionic character.

Step-by-step solution

Understanding the Basicity of Oxides

Basicity of oxides refers to how easily an oxide can accept protons. In the context of metal oxides, those that are more ionic tend to be more basic.

Group Trend in the Periodic Table

Magnesium (Mg) and Barium (Ba) are both elements in Group 2 of the periodic table, also known as the alkaline earth metals. As you move down the group from Mg to Ba, the size of the atoms increases.

Ionic Character

As the atomic size increases, the ionic character of the oxides also increases due to the decreased attraction between the metal cation and the oxide anion. Hence, the metal oxides of heavier elements are more basic.

Comparing MgO and BaO

Considering the aforementioned points, \(\mathrm{BaO}\) (Barium Oxide) is more basic than \(\mathrm{MgO}\) (Magnesium Oxide) because Barium is further down the group than Magnesium, resulting in a larger ion and more ionic oxide.

Key concepts

Ionic Character

Ionic character can influence the properties of oxides, especially regarding their basicity. In a compound, ionic character relates to the extent of charge separation between its constituent ions. This property is pivotal in determining how strongly the ions interact with each other. When discussing metal oxides, particularly those formed by alkaline earth metals, understanding ionic character becomes crucial.

As you move down a group in the periodic table, the size of the metal cations increases. This results in a decrease in the effective nuclear charge experienced by the outermost electrons. Consequently, there is less attraction between the positive metal cation and the negative oxide anion, which enhances the ionic nature of the bond. A greater ionic character means that the ions are more likely to dissociate in solution, thus increasing the oxide's basicity. For example,

• Magnesium Oxide (\( \mathrm{MgO} \)) is less ionic due to stronger attraction between smaller ions.
• Barium Oxide (\( \mathrm{BaO} \)) is more ionic, resulting in higher basicity.

Alkaline Earth Metals

Alkaline earth metals belong to Group 2 in the periodic table and include magnesium, calcium, strontium, barium, and radium. These metals are characterized by having two electrons in their outermost energy level. This electron configuration lends itself to forming divalent cations with a charge of +2.

These elements are typically shiny and, similar to alkali metals in Group 1, they are highly reactive. However, their reactivity is not as intense as that of their Group 1 neighbors. When it comes to oxides, alkaline earth metals form compounds that are fundamentally basic due to the donation of electrons that results in oxide anions (\( \mathrm{O}^{2-} \)).

• As you move down the group from magnesium to barium, the basicity of their oxides increases.
• The increasing basicity is due to enhanced ionic character and a greater tendency to donate electrons.

These properties and trends help understand why barium oxide (\( \mathrm{BaO} \)) is more basic than magnesium oxide (\( \mathrm{MgO} \)).

Periodic Table Trends

Trends in the periodic table offer a systematic method to predict the behavior of elements based on their position. One essential trend that impacts the properties of elements and their compounds is how atomic and ionic sizes change.

As you move down a group in the periodic table, the size of both the atoms and ions increases. This is due to the addition of more electron shells. Additionally, there is a concurrent decrease in effective nuclear charge felt by the outer electrons, making these larger atoms less tightly held.

• This increase in size down a group, such as in alkaline earth metals, leads to a higher ionic character in their oxides.
• The increased ionic character results in more basic oxides.

Understanding such periodic trends is key to explaining why, for example, barium oxide is more basic than magnesium oxide. As students of chemistry, recognizing these trends helps simplify complex concepts of reactivity and affinity in chemical compounds.