Question

Consider the two ionic compounds \(\mathrm{NaCl}\) and \(\mathrm{CaO} .\) In which compound are the cation-anion attractive forces stronger? Explain your answer.

Short answer

The cation-anion attractive forces are stronger in CaO due to higher ionic charges.

Step-by-step solution

Identify the Ions

First, identify the ions in each compound. NaCl consists of Na⁺ and Cl⁻ ions, while CaO consists of Ca²⁺ and O²⁻ ions.

Understand Coulomb's Law

Coulomb's Law tells us that the force of attraction between two charged particles is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. The formula is: \[ F = k \frac{{|q_1 imes q_2|}}{{r^2}} \]where \( F \) is the force, \( k \) is Coulomb's constant, \( q_1 \) and \( q_2 \) are the charges, and \( r \) is the distance.

Compare the Charges

For NaCl, the charges are Na⁺ (\(+1\)) and Cl⁻ (\(-1\)), giving a product of charges \(|q_1 imes q_2| = 1\). For CaO, the charges are Ca²⁺ (\(+2\)) and O²⁻ (\(-2\)), giving a product of charges \(|q_1 imes q_2| = 4\). Since the product of charges is greater for CaO, it indicates stronger attractive forces.

Conclude the Strength of Forces

Since the product of the charges in CaO is larger than in NaCl, and assuming comparable ionic radii, the attractive forces between Ca²⁺ and O²⁻ in CaO are stronger according to Coulomb's Law.

Key concepts

Coulomb's Law

Coulomb's Law is a fundamental principle in understanding the forces at play in ionic compounds. It describes how two charged particles interact with each other as a result of their electric charge. Essentially, the force between them can be calculated using the equation: \[ F = k \frac{{|q_1 \times q_2|}}{{r^2}} \] Where:

• \( F \) is the force of attraction or repulsion between the particles.
• \( k \) is Coulomb's constant.
• \( q_1 \) and \( q_2 \) are the magnitudes of the electric charges.
• \( r \) is the distance between the centers of the two charges.

These relations tell us that the force increases with higher charges and decreases as the distance between them grows. This is particularly important in ionic compounds where ions of opposite charges attract.

Cation-Anion Interaction

Cation-anion interaction is a key aspect of ionic bonding. In an ionic compound, a cation (positively charged ion) and an anion (negatively charged ion) attract each other to form a stable structure. For example, in sodium chloride (\(\mathrm{NaCl}\)), a sodium ion (\(\mathrm{Na^+}\)) attracts a chloride ion (\(\mathrm{Cl^-}\)). Similarly, in calcium oxide (\(\mathrm{CaO}\)), a calcium ion (\(\mathrm{Ca^{2+}}\)) is strongly attracted to an oxide ion (\(\mathrm{O^{2-}}\)).

The strength of this interaction is dictated by the charge of the ions involved. In \(\mathrm{NaCl}\), the interaction involves single charges (\(\mathrm{Na^+}\) and \(\mathrm{Cl^-}\)). However, in \(\mathrm{CaO}\), the charges are doubled (\(\mathrm{Ca^{2+}}\) and \(\mathrm{O^{2-}}\)), enhancing the attraction. When considering cation-anion interactions, it's clear that greater charges can lead to stronger binding when other factors such as ionic size are similar.

Chemical Bonding

Chemical bonding describes the process by which atoms or molecules are held together in compounds. In ionic compounds, the type of chemical bonding present is ionic bonding. This occurs when complete transfer of electrons happens from a metal to a non-metal, resulting in the formation of ions. These oppositely charged ions then attract each other, forming a stable ionic compound.

Taking \(\mathrm{NaCl}\) and \(\mathrm{CaO}\) as examples, the bond formation in these compounds involves a transfer of electrons. Sodium transfers one electron to chlorine, creating \(\mathrm{Na^+}\) and \(\mathrm{Cl^-}\) ions. In \(\mathrm{CaO}\), calcium transfers two electrons to the oxygen atom, resulting in \(\mathrm{Ca^{2+}}\) and \(\mathrm{O^{2-}}\) ions. This electron transfer leads to strong electrostatic forces of attraction, anchoring the ions in place and establishing the ionic bond. Understanding these principles allows us to predict and compare the relative strengths and characteristics of different ionic compounds.