Problem 31 - Chemistry: The Central Science in SI Units, Global Edition

Question

(a) State whether or not the bonding in each substance is likely to be covalent: (i) glucose, (ii) nitrogen, (iii) aluminum hydroxide, (iv) ammonia, (v) neon. (b) A substance, XY, formed from two different elements, melts at \(350^{\circ} \mathrm{C}\). Is XY likely to be a covalent or an ionic substance?

Step-by-Step Solution

Answer

(a) (i) Covalent, (ii) Covalent, (iii) Not covalent (ionic), (iv) Covalent, (v) No bond (neon is a noble gas). (b) XY is more likely to have an ionic bond due to its \(350^{\circ} \mathrm{C}\) melting point.

Step 1: (a) Determine the type of bonding in each substance

In order to identify if the bonding in each substance is likely covalent, we can analyze the types of elements involved in the chemical. (i) Glucose (C6H12O6): Glucose consists of non-metal elements (carbon, hydrogen, and oxygen), and it is a molecular compound. Hence, its bond is covalent. (ii) Nitrogen (N2): Nitrogen is a diatomic molecule and consists of the same non-metal element (nitrogen). It forms a covalent bond with itself. (iii) Aluminum hydroxide (Al(OH)3): Aluminum hydroxide consists of a metal (aluminum) bonded to a polyatomic ion (hydroxide). This type of bond is ionic, so it is not covalent. (iv) Ammonia (NH3): Ammonia consists of non-metal elements (nitrogen and hydrogen) and is a molecular compound. Hence, the bond in ammonia is covalent. (v) Neon (Ne): Neon is a noble gas, and it has a full valence electron shell. Noble gases do not form bonds; therefore, there is no covalent bond in neon.

Step 2: (b) Determine the type of bonding in substance XY

Substance XY is formed from two different elements and has a melting point of \(350^{\circ} \mathrm{C}\). Based on this information, we can determine whether XY is likely a covalent or an ionic substance. Ionic substances typically have high melting points (above \(300^{\circ} \mathrm{C}\)). So, since the melting point of XY is \(350^{\circ} \mathrm{C}\), it is suggestive that XY might have an ionic bond. On the other hand, covalent substances usually have lower melting points (below \(300^{\circ} \mathrm{C}\)). However, some covalent substances may have melting points slightly above \(300^{\circ} \mathrm{C}\). Given the melting point of XY and considering the historical melting points of known ionic and covalent substances, it is more likely that XY has an ionic bond rather than a covalent bond.

Key Concepts

Ionic Bonding

Ionic bonding is a type of chemical bond where atoms transfer electrons to achieve a more stable electron configuration, mimicking the electron arrangement of noble gases. This type of bonding typically occurs between metals and non-metals. In ionic bonds, the metal loses electrons to become a positively charged ion, whereas the non-metal gains those electrons to become a negatively charged ion. The opposite charges then attract each other, forming a strong bond. Understanding ionic bonding can help explain why substances like sodium chloride (table salt) form crystal lattices and have high melting and boiling points. The attraction between ions is so strong that substantial energy is needed to separate them, hence the high melting and boiling points. Key Characteristics of Ionic Bonding

• Involves the transfer of electrons from metal to non-metal.
• Results in the formation of positive and negative ions.
• Creates strong attractions between oppositely charged ions.
• Substances are usually solid at room temperature and have high melting points.

Chemical Compounds

Chemical compounds are substances formed from the chemical bonding of two or more different elements. These compounds have unique properties that differ from the independent elements that form them. Chemical compounds can be classified based on the type of bonding present: ionic or covalent. Types of Chemical Compounds

• Ionic Compounds: Formed through ionic bonding, they usually consist of a metal and a non-metal. Ionic compounds are characteristically crystalline solids with high melting points.
• Covalent Compounds: Formed through covalent bonding, where atoms share electrons, typically between non-metals.

By understanding the different types of chemical compounds, students can better predict the properties and behaviors of various substances. This insight is particularly useful in fields like chemistry, materials science, and environmental science. Chemical compounds are the foundation of many natural and man-made processes, from the molecules making up our DNA to the materials used in modern technology.

Molecular Compounds

Molecular compounds are a type of chemical compound where atoms bond through covalent bonding, sharing electrons rather than transferring them. This type of bonding predominantly occurs between non-metal atoms. An example of a molecular compound that is common and vital to life is water ( H_2O ), formed by the sharing of electrons between hydrogen and oxygen atoms. Attributes of Molecular Compounds

• Typically have low melting and boiling points compared to ionic compounds.
• Can exist in different states: gases (like oxygen, O_2 ), liquids (like water), or solids (like glucose, C_6H_{12}O_6 ) at room temperature.
• Generally poor conductors of electricity due to the lack of free ions.

Molecular compounds are fundamental to understanding many biological processes and chemical reactions. They provide critical insight into how organic life forms and sustains itself, as well as how various synthetic substances are created and utilized in numerous industries. Understanding the bonds and interactions in molecular compounds is essential for fields ranging from healthcare to renewable energy.