Question

Two elements \(X\) and \(Y\) combine to form a compound \(X Y\). Under what conditions the bond formed between them will be lonic? (a) If the difference in electronegativities of \(X\) and \(Y\) is \(1.7 .\) (b) If the difference in electronegativities of \(X\) and \(Y\) is more than \(1.7\). (c) If the difference in electronegativities of \(X\) and \(Y\) is less than \(1.7\). (d) If both \(X\) and \(Y\) are highly electronegative.

Short answer

The bond between X and Y will be ionic if the difference in electronegativities is greater than 1.7, so the correct answer is (b).

Step-by-step solution

Understanding Ionic Bonds

A bond is considered ionic when there is a complete transfer of electrons from one atom to another. This usually happens between a metal and a nonmetal. For an ionic bond to form, one atom must be able to donate electrons easily (low electronegativity) while the other must have a strong tendency to gain electrons (high electronegativity).

Electronegativity Difference Threshold

The electronegativity difference between two bonding atoms is a strong indicator of the type of bond that will form. A large difference in electronegativity typically leads to an ionic bond. This is commonly accepted to occur when the difference is greater than 1.7 according to the Pauling scale.

Analyzing Options for Ionic Bond Conditions

Checking each option: (a) A difference of 1.7 is right on the typical threshold for ionic bonds. (b) A difference greater than 1.7 strongly suggests an ionic bond. (c) A difference less than 1.7 tends to indicate a polar covalent bond rather than an ionic bond. (d) If both elements are highly electronegative, they are unlikely to form an ionic bond as neither will easily donate its electrons.

Key concepts

Electronegativity Difference

To grasp the notion of electronegativity difference, imagine two friends with differing appetites for chocolate. If one has a much more intense craving, they are more likely to end up with the chocolate bar. Similarly, in chemistry, atoms have varying appetites for electrons, known as electronegativity. The measure of an atom's tendency to attract and hold onto electrons when bonded with another atom is crucial in determining the type of bond that will form.

When we compare the electronegativity of two atoms, if the difference is significant - generally accepted as greater than 1.7 - the one with higher electronegativity will more aggressively pull electrons towards itself. This often results in the electron(s) being completely transferred, creating an ionic bond. If one atom is a champion electron attractor (nonmetal) and the other is more generous with its electrons (metal), imagine an intense tug-of-war where the stronger player wins outright, taking the electron for itself, which leads to the creation of ions and the establishment of an ionic bond.

Metal and Nonmetal Bonding

Diving into the realm of metal and nonmetal bonding, picture a dance between two partners with different styles. Metals, which are typically shiny, malleable elements, like to lead by giving away their outer electrons, while nonmetals, diverse in characteristics, prefer to follow by taking on additional electrons to fill their outer shell.

When these two types of elements come into bond, their contrasting electron behaviors set the stage for an ionic bond. Metals, with low electronegativity, easily lose electrons and become positively charged ions (cations). On the other hand, nonmetals, with higher electronegativity, readily gain those electrons to become negatively charged ions (anions). This opposite charge attraction is the dramatic finale of their dance, solidifying their bond into a stable, neutral compound. This is why when you pair a metal and a nonmetal, you often end up with an ionic compound, as their electron exchange leads to an undeniable attraction.

Pauling Scale

The Pauling Scale is like a leaderboard for atom competitiveness in attracting electrons. Developed by the renowned chemist Linus Pauling, this scale assigns a value to each element that reflects its electronegativity or electron-drawing power. The higher the value, the stronger the atom is in the electron tug-of-war.

It ranges from around 0.7, which is a lightweight contender like francium, to 4.0, a heavyweight champion like fluorine. By consulting this scale, chemists can predict the nature of the bond between two atoms. If the electronegativity difference according to the Pauling scale is above 1.7, it’s akin to a heavyweight versus a lightweight; the electron is almost certainly transferred, tipping the balance toward an ionic bond. This scale, and its 1.7 cutoff, is a powerful tool for predicting when an ionic bond will form, helping to classify compounds and understand their behaviors.