Question

The increasing order of ionic character of CsF, LiI, \(\mathrm{NaBr}\) and \(\mathrm{KCl}\) is: (a) \(\mathrm{CaF}<\mathrm{KCl}<\mathrm{NaBr}<\mathrm{LiI}\) (b) \(\mathrm{NaBr}<\mathrm{KCl}<\mathrm{LiI}<\mathrm{CsF}\) (c) \(\mathrm{LiI}<\mathrm{KCl}<\mathrm{CsF}<\mathrm{NaBr}\) (d) \(\mathrm{LiI}<\mathrm{NaBr}<\mathrm{KCl}<\mathrm{CsF}\)

Short answer

The correct order is (d) LiI < NaBr < KCl < CsF.

Step-by-step solution

Understanding Ionic Character

The ionic character of a compound refers to the degree to which an electron is transferred from one atom to another, forming a charged ion. In general, ionic character is influenced by the differences in electronegativity between the metal and non-metal atoms. The greater the difference, the more ionic the bond.

Analyzing the Compounds

The compounds in question are CsF, LiI, NaBr, and KCl. We need to identify the electronegativity difference between each metal and the respective halogen. Typically, fluorine is the most electronegative and iodine the least, while cesium is less electronegative than lithium.

Electronegativity Differences

1. CsF: Cesium (Cs) with Fluorine (F) has the highest electronegativity difference. 2. LiI: Lithium (Li) with Iodine (I) has the lowest electronegativity difference. 3. KCl: Potassium (K) with Chlorine (Cl) and NaBr: Sodium (Na) with Bromine (Br) have moderate electronegativity differences, with KCl generally higher than NaBr.

Arranging the Compounds by Ionic Character

Based on the electronegativity differences, the order from least to most ionic character is determined: 1. LiI (least ionic due to smallest difference) 2. NaBr 3. KCl 4. CsF (most ionic due to highest difference)

Identifying the Correct Option

The correct order identified is: LiI < NaBr < KCl < CsF. This corresponds to option (d).

Key concepts

Electronegativity Differences

Electronegativity refers to the ability of an atom to attract shared electrons in a chemical bond. When we talk about electronegativity differences, we're discussing how much more one atom attracts electrons compared to the other in a bond.

• If two atoms have a large electronegativity difference, the bond between them is likely to be more ionic. This means electrons are transferred rather than shared, leading to the formation of ions.
• A smaller difference implies a more covalent bond, where atoms share electrons more equally.

One of the key factors in determining the ionic character of a bond is precisely this electronegativity difference. For students looking to understand ionic versus covalent bonds, focusing on these differences helps in predicting the nature of the compound.

CsF

Cesium fluoride (CsF) represents a strong ionic bond due to the significant electronegativity difference between cesium (Cs) and fluorine (F).

• Fluorine is the most electronegative element, making it very effective at pulling electrons towards itself.
• Conversely, cesium is one of the least electronegative metals, allowing it to easily give up its electron.
• This stark difference makes CsF one of the most ionic compounds in terms of its character.

Understanding the properties of CsF helps in studies involving ionic conductivity and solubility. It's a textbook example of a compound with high ionic character due to the prominent electronegativity disparity.

LiI

Lithium iodide (LiI) exhibits lower ionic character. This is primarily because iodine (I) is much less electronegative than fluorine, while lithium (Li) does not have as low an electronegativity as cesium.

• The electronegativity difference in LiI is less pronounced, leading to a more covalent character of this bond.
• LiI tends to dissolve slightly differently compared to other ionic compounds due to its polarizability, stemming from a partial overlap of electronic clouds.
• This reduced ionic nature affects its uses and behaviors, particularly in its role as a mild reducing agent.

When comparing ionic characters, LiI often sits at the lower end of the scale, with its bond exhibiting notable covalent character.

NaBr

Sodium bromide (NaBr) finds itself in between the extremes of ionic versus covalent character. This compound results from the bond between sodium (Na) and bromine (Br).

• While sodium is a metal prone to losing an electron, bromine is less electronegative than chlorine but more than iodine, thus offering a moderate electronegativity difference.
• This means NaBr forms a stable ionic bond, but not as 'ionic' as the likes of CsF.
• NaBr is commonly used in photography and medicine, exploited for its moderate ionic nature and solubility.

When considering bonds in a periodic table context, NaBr serves as a middle-ground example. Its placement provides insight into chemical bonding and aids in educational discussions about ionic character characteristics.