Question

What kind of bonding (ionic or covalent) would you predict for the products resulting from the following combinations of elements? (a) \(\mathrm{Na}+\mathrm{I}_{2}\) (b) \(\mathrm{C}+\mathrm{S}_{8}\) (c) \(\mathrm{Mg}+\mathrm{Br}_{2}\) (d) \(\mathrm{P}_{4}+\mathrm{Cl}_{2}\)

Short answer

(a) Ionic, (b) Covalent, (c) Ionic, (d) Covalent.

Step-by-step solution

Determine the Type of Elements Involved

To predict the type of bonding, first identify whether the elements are metals or non-metals. Metals tend to lose electrons and form cations, while non-metals tend to gain electrons and form anions. In this exercise, we have:- (a) Sodium (Na) is a metal, Iodine (\[\mathrm{I}_2\]) is a non-metal.- (b) Carbon (C) and Sulfur (\[\mathrm{S}_8\]) are both non-metals.- (c) Magnesium (Mg) is a metal, Bromine (\[\mathrm{Br}_2\]) is a non-metal.- (d) Phosphorus (\[\mathrm{P}_4\]) and Chlorine (\[\mathrm{Cl}_2\]) are non-metals.

Determine Potential Bonding Based on Element Types

- (a) The combination of a metal (Na) and a non-metal (\[\mathrm{I}_2\]) typically forms ionic bonds.- (b) The combination of non-metals (C and \[\mathrm{S}_8\]) typically forms covalent bonds.- (c) The combination of a metal (Mg) and a non-metal (\[\mathrm{Br}_2\]) typically forms ionic bonds.- (d) The combination of non-metals (\[\mathrm{P}_4\] and \[\mathrm{Cl}_2\]) typically forms covalent bonds.

Confirm the Bond Type for Each Combination

Now confirm the bond type prediction:- (a) \[\mathrm{Na} + \mathrm{I}_2 \rightarrow \mathrm{2NaI}\], forming \[\mathrm{Na^+}\] and \[\mathrm{I^-}\], indicates ionic bonding.- (b) Multiple covalent bonds form between \[\mathrm{C}\] and \[\mathrm{S}_8\], such as in carbon disulfide \[\mathrm{CS}_2\].- (c) \[\mathrm{Mg} + \mathrm{Br}_2 \rightarrow \mathrm{MgBr_2}\] indicates ionic bonding, forming \[\mathrm{Mg^{2+}}\] and \[\mathrm{Br^-}\].- (d) The molecule \[\mathrm{PCl_3}\] is formed as a result of covalent bonds between \[\mathrm{P}_4\] and \[\mathrm{Cl}_2\].

Key concepts

Ionic Bonding

Ionic bonding occurs when a metal and a non-metal come together, creating a bond through the transfer of electrons.

• The metal, which has a tendency to lose electrons, becomes a positively charged ion known as a cation.
• The non-metal, which tends to gain electrons, becomes a negatively charged ion referred to as an anion.

The resulting electrostatic attraction between the oppositely charged ions forms a strong ionic bond.
In the context of chemical reactions, this type of bonding is typically observed when elements from the far left of the periodic table (such as alkali metals) react with elements from the far right (except noble gases).
For example, in the combination of sodium (\(\mathrm{Na}\)) and iodine (\(\mathrm{I}_2\)), sodium easily loses an electron to form \(\mathrm{Na^+}\) and iodine gains that electron to form \(\mathrm{I^-}\), resulting in the formation of sodium iodide (\(\mathrm{NaI}\)). Ionic compounds are typically solid at room temperature and have high melting and boiling points due to the strong attractions between ions.

Covalent Bonding

Covalent bonding is the sharing of electrons between two or more non-metals. This type of bonding allows each atom in a molecule to attain the electron configuration of a noble gas, thereby achieving stability.
Unlike ionic bonds, covalent bonds are formed through mutual sharing rather than transferring electrons. When atoms share electrons, the resulting pairs are called shared electron pairs or bonding pairs.
In the case of carbon (\(\mathrm{C}\)) and sulfur (\(\mathrm{S}_8\)), they form covalent bonds as they both are non-metals. For example, the compound carbon disulfide (\(\mathrm{CS}_2\)) is formed when carbon shares electrons with sulfur atoms, resulting in multiple covalent bonds. Covalent compounds usually exist in different physical states at room temperature and can have various melting and boiling points depending on the strength and number of bonds.

Metal and Non-Metal Interactions

Metal and non-metal interactions are key to understanding the formation of ionic compounds. When these two types of elements interact, different properties are exhibited that are distinct from either pure metals or non-metals.

• Metals, like magnesium (\(\mathrm{Mg}\)), typically have low ionization energies, which means they can lose electrons easily.
• Non-metals, such as bromine (\(\mathrm{Br}_2\)), have high electron affinities, so they readily gain electrons.

In this case, when magnesium and bromine react, magnesium loses two electrons to form \(\mathrm{Mg^{2+}}\), and each bromine atom gains one electron to form \(\mathrm{Br^-}\). This transfer leads to the formation of magnesium bromide (\(\mathrm{MgBr_2}\)), an ionic compound with a stable, lattice structure. Such interactions explain why ionic compounds are often robust and have high conductivity when dissolved in water, as the ions become free to move and carry electric current.

Periodic Table Trends

Periodic table trends help predict the type of bonding that is likely to occur between elements. Elements are arranged in an order that reflects recurring patterns or trends:

• Ionic bonds tend to form between elements on opposite sides of the periodic table. Metals are typically on the left, and non-metals are on the right.
• Covalent bonds are more common among elements with similar electronegativities, typically those located closer to each other on the right side.

Understanding the position of an element on the periodic table provides insight into its properties and its preferred type of bonding. For example, phosphorus (\(\mathrm{P}_4\)) and chlorine (\(\mathrm{Cl}_2\)) are both non-metals positioned towards the right of the periodic table. As a result, they form covalent bonds, as seen in phosphorus trichloride (\(\mathrm{PCl_3}\)). By recognizing these periodic trends, one can predict and understand bonding behavior in various chemical reactions more effectively.