Question

Alkaline earth metals are involved in two key diagonal relationships in the periodic table. (a) Give the two pairs of elements in these diagonal relationships. (b) For each pair, cite two similarities that demonstrate the relationship. (c) Why are the members of each pair so similar in behavior?

Short answer

The pairs are Be-Al and Mg-Li. Similarities: Be and Al form covalent compounds and exhibit amphoteric behavior; Mg and Li react with water and form similar ionic compounds. They are similar due to size and charge density.

Step-by-step solution

- Identify the Diagonal Relationships

Diagonal relationships occur between elements that are diagonally adjacent in the periodic tableand belong to adjacent groups. The key pairs involving alkaline earth metals are:1. Beryllium (Be) and Aluminum (Al)2. Magnesium (Mg) and Lithium (Li)

- Similarities for Beryllium and Aluminum

1. Both Be and Al form covalent compounds and have a tendency to form complexes with ligands.2. Both exhibit amphoteric behavior, meaning they can act as both acids and bases in reactions.

- Similarities for Magnesium and Lithium

1. Both Mg and Li react with water to form hydroxides, releasing hydrogen gas.2. Both form ionic compounds with similar lattice structures, such as MgCl2 and LiCl.

- Explanation for Similar Behavior

The members of each pair exhibit similar behavior due to their similar sizes and charge density,which influence their chemical reactivity and the types of bonds they form. Despite being in different groups,their diagonal positioning minimizes the overall difference in periodic properties.

Key concepts

alkaline earth metals

Alkaline earth metals are elements in Group 2 of the periodic table. They include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). These metals are highly reactive, though not as reactive as their Group 1 counterparts. They share common characteristics such as having two valence electrons, which they readily lose to form divalent cations (e.g., Be²⁺, Mg²⁺). These metals are typically shiny and are good conductors of electricity. Alkaline earth metals form various compounds, notably oxides and hydroxides, which feature prominently in many chemical reactions.

periodic table trends

Periodic table trends help us understand the properties and behavior of elements based on their position in the table. Key trends include:

• Atomic radius: Increases down a group and decreases across a period.
• Electronegativity: Decreases down a group and increases across a period.
• Ionization energy: Decreases down a group and increases across a period.

These trends explain why elements exhibit certain characteristics. Diagonal relationships occur when elements in different groups (but adjacent periods) show similar properties due to balanced effects of these trends. For example, beryllium (Be) in Group 2 and aluminum (Al) in Group 13 exhibit similar behaviors due to these trends.

chemical reactivity

Chemical reactivity refers to the tendency of a substance to engage in chemical reactions. Alkaline earth metals are quite reactive. Their reactivity generally increases down the group; for example, magnesium (Mg) reacts less vigorously with water than calcium (Ca). Reactivity depends on the ease with which an element can lose or gain electrons, forming ionic or covalent bonds. Diagonal relationships in the periodic table can also influence chemical reactivity. Beryllium (Be) and aluminum (Al) both have a tendency to form covalent rather than ionic compounds due to their similar atomic sizes and charge densities.

covalent compounds

Covalent compounds are chemical compounds where atoms are bonded by sharing pairs of electrons. Unlike ionic compounds, which are formed through the transfer of electrons, covalent compounds generally occur between nonmetals. However, due to the diagonal relationships in the periodic table, some metals like beryllium (Be) and aluminum (Al) also form covalent compounds. These elements tend to form complexes with ligands, meaning they can bind with other molecules or ions. Beryllium chloride (BeCl₂) and boron trichloride (BCl₃) are examples of covalent compounds formed by elements showing diagonal relationships.

amphoteric behavior

Amphoteric behavior refers to the ability of a substance to act as both an acid and a base. This behavior is observed in some elements and their compounds. For instance, beryllium (Be) and aluminum (Al), which are in a diagonal relationship, both demonstrate amphoteric behavior. They can react with acids to form salts and release hydrogen, and with bases to form complex ions. Beryllium oxide (BeO) and aluminum oxide (Al₂O₃) are classic examples of amphoteric oxides. This dual behavior is advantageous in various chemical processes, enabling these substances to participate in a wide range of reactions.