Question

The correct order of increasing ionic character is: (a) \(\mathrm{BeCl}_{2}<\mathrm{MgCl}_{2}<\mathrm{BaCl}_{2}<\mathrm{CaCl}_{2}\) (b) \(\mathrm{BeCl}_{2}<\mathrm{MgCl}_{2}<\mathrm{CaCl}_{2}<\mathrm{BaCl}_{2}\) (c) \(\mathrm{BaCl}_{2}<\mathrm{CaCl}_{2}<\mathrm{MgCl}_{2}<\mathrm{BeCl}_{2}\) (d) \(\mathrm{BeCl}_{2}<\mathrm{BaCl}_{2}<\mathrm{MgCl}_{2}<\mathrm{CaCl}_{2}\)

Short answer

(b) \( \mathrm{BeCl}_{2}<\mathrm{MgCl}_{2}<\mathrm{CaCl}_{2}<\mathrm{BaCl}_{2} \) is the correct order of increasing ionic character.

Step-by-step solution

Understand Ionic Character

Ionic character refers to the extent to which a compound exhibits ionic bonding versus covalent bonding. Higher ionic character means a compound is more ionic.

Consider the Metal Position in the Periodic Table

Ionic character generally increases with the size of the metal cation because larger cations are less able to polarize the anion. Elements lower in the group in the periodic table will typically have greater ionic character.

Compare Metal Cations in the Options

The metals in question, Beryllium (Be), Magnesium (Mg), Calcium (Ca), and Barium (Ba) belong to Group 2 (alkaline earth metals) in the periodic table. Their order, based on increasing ionic character due to increase in size and decrease in polarization power, is Be, Mg, Ca, Ba.

Match with Given Options

The correct order from lowest to highest ionic character should reflect Be having the least and Ba having the most. Option (b) \( \mathrm{BeCl}_{2}<\mathrm{MgCl}_{2}<\mathrm{CaCl}_{2}<\mathrm{BaCl}_{2} \) matches this order.

Key concepts

Alkaline Earth Metals

The alkaline earth metals are a group of elements found in Group 2 of the periodic table. They include Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra). These metals have two electrons in their outer shell, making them quite reactive, though not as reactive as alkali metals.

Here are a few important things to know about alkaline earth metals:

• They have a shiny, silvery-white appearance and are good conductors of electricity.
• These metals are typically found in compounds rather than in their pure form in nature.
• They readily form ionic bonds, especially with halogens, by losing their two outer electrons to form cations with a 2+ charge.

Understanding the positioning of these elements in the periodic table is crucial when predicting their chemical behavior, especially their ability to form ionic bonds.

Ionic Bonding

Ionic bonding occurs when atoms transfer electrons to achieve a full outer shell of electrons, resulting in the formation of ions. Metals such as alkaline earth metals tend to lose electrons to become positively charged cations, while non-metals tend to gain electrons to become negatively charged anions.

### Key Characteristics of Ionic Bonding

• Ions are held together by strong electrostatic forces of attraction between oppositely charged ions.
• This type of bonding typically results in the formation of crystalline solids, like salts, which are brittle and have high melting and boiling points.
• Ionic compounds conduct electricity when melted or dissolved in water because the ions are free to move.

Alkaline earth metals readily form ionic bonds because they can easily lose their two valence electrons, creating stable cations that pair well with anions like chloride (Cl⁻).

Periodic Table Trends

The periodic table organizes elements based on their atomic number, electron configurations, and recurring chemical properties. Understanding these trends helps predict the behavior of elements, such as ionic character as seen with alkaline earth metals.

### Key Trends Related to Ionic Character

• **Atomic Size:** As you move down a group in the periodic table, atomic size increases. Larger atoms have more electron shells, which affects their chemical interactions.
• **Ionization Energy:** Generally decreases down a group, meaning it's easier for atoms to lose electrons and form cations.
• **Ionic Character:** As you move down Group 2 (alkaline earth metals), ionic character generally increases. This happens because larger atoms are less effective at polarizing anions, thereby forming more ionic and less covalent bonds.

These trends are useful for predicting how an element might react, especially in forming compounds with other elements. For alkaline earth metals, the increasing ionic character from Be to Ba explains why option (b) BeCl₂ < MgCl₂ < CaCl₂ < BaCl₂ was correct.