(b) A substance, XY, formed from two different elements, melts at −33 °C. Is XY likely to be a covalent or an ionic substance?

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insert step 1> Identify the characteristics of covalent and ionic substances.

insert step 2> Consider the melting point of the substance XY, which is -33 °C.

insert step 3> Compare the melting point of XY with typical melting points of covalent and ionic substances.

insert step 4> Recall that ionic compounds generally have high melting points due to strong electrostatic forces between ions.

insert step 5> Conclude that a low melting point, like -33 °C, suggests that XY is likely a covalent substance, as covalent compounds typically have lower melting points.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Covalent vs. Ionic Bonds

Covalent bonds form when two nonmetals share electrons, resulting in molecules with lower melting and boiling points. In contrast, ionic bonds occur between metals and nonmetals, where electrons are transferred, creating charged ions that attract each other, typically resulting in higher melting points.

Melting Point as an Indicator

The melting point of a substance can provide insight into its bonding type. Generally, substances with ionic bonds have higher melting points due to the strong electrostatic forces between ions, while covalent compounds often have lower melting points due to weaker intermolecular forces.

Properties of Molecular Compounds

Molecular compounds, which are often formed by covalent bonds, tend to have distinct properties such as lower melting points, volatility, and poor electrical conductivity in solid form. The melting point of −33 °C suggests that XY is likely a molecular compound, indicating it is more likely to be covalent.

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(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.

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(a) Based on the lattice energies of MgCl2 and SrCl2 given in Table 8.1, what is the range of values that you would expect for the lattice energy of CaCl2?

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Textbook Question

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