Problem 166 - Introductory Chemistry Atoms First

Question

Arrange in order of increasing ionic character: \(\mathrm{CsBr}, \mathrm{KBr}, \mathrm{PBr}_{3} \mathrm{MgBr}_{2}\)

Step-by-Step Solution

Answer

The order of increasing ionic character for the given compounds, based on electronegativity differences, is: \(PBr_3 < MgBr_2 < KBr < CsBr\).

Step 1: List the electronegativity values of the elements involved

Refer to a periodic table or electronegativity chart for the electronegativity values (Pauling scale) of the elements in question: Cesium (Cs): 0.79 Potassium (K): 0.82 Phosphorus (P): 2.19 Magnesium (Mg): 1.31 Bromine (Br): 2.96

Step 2: Calculate electronegativity differences for each compound

Calculate the absolute electronegativity differences for each bond in the given compounds: CsBr: |2.96 - 0.79| = 2.17 KBr: |2.96 - 0.82| = 2.14 PBr₃: |2.96 - 2.19| = 0.77 (P-Br bond) MgBr₂: |2.96 - 1.31| = 1.65

Step 3: Arrange compounds in increasing order of electronegativity difference

Arrange the compounds in order according to the electronegativity differences from step 2, in ascending order (lowest to highest): PBr₃ < MgBr₂ < KBr < CsBr Thus, the order of increasing ionic character is: PBr₃, MgBr₂, KBr, CsBr.

Key Concepts

Electronegativity

Electronegativity is a property of an atom in a molecule that indicates its ability to attract shared electrons in a chemical bond. The concept of electronegativity is central to understanding the nature of ionic and covalent bonds. It helps predict how electrons will distribute in compounds.
A high electronegativity means an atom strongly attracts electrons, pulling them closer. Conversely, a low electronegativity indicates a weaker attraction.

• Atoms with greater differences in electronegativity are more likely to form ionic bonds.
• If the difference is small, the bond is more covalent in character.
• Elements on the right side of the periodic table, especially nonmetals like fluorine and oxygen, often have high electronegativity values.

Pauling Scale

The Pauling Scale, developed by Linus Pauling, is a numerical scale that quantifies the electronegativity of elements. It is the most commonly used scale for this purpose. Each element is assigned a value, generally between 0.7 and 4.0.
The values are dimensionless but offer a relative measure of how strongly atoms attract bonding electrons.

• Fluorine is the most electronegative element with a value of about 4.0.
• Cesium, one of the least electronegative atoms, has a value of about 0.7.
• The differences in values indicate that if two bonded atoms have a large electronegativity difference, the bond tends to be ionic.

Ionic Bonds

Ionic bonds are a type of chemical bond formed through the electrostatic attraction between oppositely charged ions. This occurs when one atom transfers its electrons to another atom, typically happening between a metal and a non-metal.
Key Characteristics of Ionic Bonds:

• They typically form between elements with a large difference in electronegativity (usually more than 1.7 on the Pauling scale).
• These bonds result in the formation of a lattice structure at solid state, which is characteristic of ionic compounds.
• Compounds with ionic bonds generally have high melting and boiling points.
• Ionic bonds are also responsible for conducting electricity in molten or aqueous states.

Chemical Compounds

Chemical compounds are substances formed when two or more elements are chemically bonded together. They can be broadly classified into ionic and covalent compounds based on the nature of the bonds.
Understanding the **ionic character** in compounds is essential.

• Compounds with predominantly ionic bonds are called ionic compounds. They are typically formed between metals and non-metals.
• Covalent compounds have bonds formed by shared electrons and generally occur between non-metal atoms.
• The properties like solubility, electrical conductivity, and color vary depending on the type of bonding within the compound.
• Measurement of electronegativity helps us predict the type of chemical bonding in a compound.