Question

Which of the following statements are true regarding an ionic bond between cobalt and sulfur in a CoS formula unit? (a) Cobalt and sulfide ions bond by electrostatic attraction. (b) Cobalt atoms gain electrons and sulfur atoms lose electrons. (c) The ionic radius of a cobalt ion is greater than its atomic radius. (d) Breaking an ionic bond between cobalt and sulfur requires energy.

Short answer

Statements (a) and (d) are true.

Step-by-step solution

Understanding Ionic Bonds

Ionic bonds form between metal and non-metal atoms. The metal loses electrons to become a cation, and the non-metal gains electrons to become an anion. Then, these oppositely charged ions attract each other due to electrostatic forces, forming an ionic bond.

Evaluating Statement (a)

The statement says cobalt and sulfide ions bond by electrostatic attraction. This is true because in ionic bonding, cations and anions are held together by electrostatic attraction, which is the defining characteristic of ionic bonds.

Evaluating Statement (b)

The statement claims cobalt atoms gain electrons and sulfur atoms lose electrons. For an ionic bond, the opposite is true: the metal cobalt loses electrons to form a cation, and the non-metal sulfur gains those electrons to form an anion. Therefore, this statement is false.

Evaluating Statement (c)

The statement suggests that the ionic radius of a cobalt ion is greater than its atomic radius. However, when cobalt loses electrons to form a cation, the removal of electrons results in a smaller electron cloud, making the ionic radius smaller than the atomic radius. Hence, this statement is false.

Evaluating Statement (d)

Breaking an ionic bond between cobalt and sulfur requires energy because the ions are held together by strong electrostatic forces, which need to be overcome for the bond to break. This statement is true.

Key concepts

Cation and Anion Formation

The formation of cations and anions is a key process in the development of ionic bonds. A cation is a positively charged ion, which forms when a metal atom, like cobalt, loses one or more electrons. The loss of electrons results in a positive charge because the number of protons (positive) exceeds the number of electrons (negative). On the other hand, an anion is a negatively charged ion, formed when a non-metal atom, such as sulfur, gains electrons. This gain of electrons results in a negative charge due to the excess of electrons over protons. The ability of different atoms to lose or gain electrons depends significantly on their position in the periodic table. Metals, usually found on the left side, are more likely to lose electrons, while non-metals, on the right, readily gain electrons to achieve a full outer shell, often reaching a stable electronic configuration similar to noble gases. Understanding the motivation and behavior behind atoms becoming cations or anions continues to be a foundational concept in chemistry, aiding us in understanding how bonds form and why certain elements interact the way they do.

Electrostatic Attraction

Electrostatic attraction is the force that glues together the cations and anions in an ionic bond. After cobalt forms a cation and sulfur an anion, their opposite charges create a powerful attraction. This attraction is due to the fundamental rule that oppositely charged particles attract each other. This principle not only helps pair cobalt ions with sulfide ions in a compound like CoS, but it is also the cornerstone of ionic bonding universally. The strength of this attraction largely depends on the charge and size of the ions. Generally, larger charge magnitudes result in stronger attractions, while smaller ionic sizes allow ions to get closer, intensifying the attraction. It's this electrostatic force that holds the ionic lattice together, giving ionic compounds their characteristic properties such as high melting and boiling points. This force is the reason why significant energy is needed to break these bonds, illustrating the stability and strength of ionic compounds.

Atomic and Ionic Radius

The concept of atomic and ionic radius is crucial in understanding how atoms change size when they become ions. The atomic radius is the distance from the nucleus to the outermost electrons in an atom. When an atom like cobalt becomes a cation by losing electrons, the decrease in electron repulsion leads to a smaller radius. This means the ionic radius of a cobalt ion is smaller than its atomic radius. This is true for all metals forming cations, as losing electrons diminishes the electron cloud around the nucleus, bringing the remaining electrons closer to the center. Conversely, when non-metals like sulfur form anions by gaining electrons, the increased repulsion among the extra electrons expands the electron cloud, increasing its ionic radius compared to its atomic radius. Understanding these changes in size helps us predict the behavior of ions in various environments, making the concepts of atomic and ionic radius essential for grasping more complex chemical interactions.