Question

Predict whether each of the following substances is likely to have a relatively high or low boiling point. (a) \(\mathrm{TlCl}_{3}\) (d) \(\mathrm{CaO}\) (b) \(\mathrm{CsCl}\) (e) \(\mathrm{O}_{2}\) (c) \(\mathrm{CO}_{2}\)

Short answer

The boiling point is likely to be highest for TlCl3, followed by CaO, then CsCl. It's likely to be lower for O2 and CO2, with O2 likely to have a lower boiling point than CO2 because O2 is a smaller molecule.

Step-by-step solution

Identifying the type of bond

First thing to do is to identify the type of bond in each substance. TlCl3 (thallium chloride) is an ionic compound. CaO (calcium oxide) is an ionic compound. CsCl (cesium chloride) is an ionic compound. O2 (oxygen) is a covalent molecule. CO2 (carbon dioxide) is a covalent molecule.

Predicting the boiling points of the substances

Based on the fact that covalent molecules generally have lower boiling points than ionic compounds because ionic compounds are held together by stronger electrostatic forces: TlCl3, CsCl, and CaO are likely to have relatively high boiling points because they are ionic compounds. O2 and CO2 are likely to have relatively low boiling points since they are covalent molecules.

Analyzing the ionic compounds

Among the ionic compounds, boiling point increases with charge and size of the ions in the compound. Therefore, TlCl3 is likely to have a highest boiling point, followed by CaO, and then CsCl.

Key concepts

Ionic Compounds

Ionic compounds consist of charged particles known as ions. These ions form when one atom donates an electron to another, creating positively charged cations and negatively charged anions. The resulting electrostatic attraction between these oppositely charged ions forms an ionic bond. This bond is typically very strong.

Some common properties of ionic compounds include:

• High melting and boiling points due to the strong attractions between ions.
• They are often soluble in water, allowing them to conduct electricity when dissolved.
• In solid form, ionic compounds do not conduct electricity.

For example, compounds like CaO (calcium oxide), TlCl_3 (thallium chloride), and CsCl (cesium chloride) have high boiling points. This occurs due to the intense electrostatic forces created by their ionic bonds.

Covalent Molecules

Covalent molecules form when two or more atoms share electrons to achieve a full outermost electron shell. Each shared pair of electrons creates a covalent bond. Covalent bonds can be single, double, or triple, depending on the number of shared electron pairs. The molecules formed usually have definite shapes and specific angles.

Key features of covalent molecules include:

• Lower melting and boiling points compared to ionic compounds, because the forces between molecules, known as van der Waals forces, are relatively weak.
• Poor conductivity for electricity, since there are no free ions or electrons.
• Diverse solubility; some dissolve well in water while others do not.

Examples of covalent molecules include O_2 (oxygen) and CO_2 (carbon dioxide), which both possess lower boiling points due to weaker intermolecular forces.

Electrostatic Forces

Electrostatic forces are the forces of attraction or repulsion between charged particles. In chemistry, these forces are integral to the formation of ionic bonds. When an ionic compound forms, the electrostatic attraction between the positively and negatively charged ions holds the compound together. This effect leads to high melting and boiling points.

Some key aspects of these forces include:

• Larger charges result in stronger forces, thus a higher boiling point.
• Distance between ions also influences the magnitude; closer ions create stronger forces.

In the context of ionic compounds such as TlCl_3 , CsCl , and CaO , the strength of these electrostatic forces greatly influences their physical properties.

Chemical Bonding Analysis

Chemical bonding analysis involves examining the types of bonds present in a substance to determine its properties, including boiling and melting points. To analyze chemical bonds, it's crucial to understand both ionic and covalent bonding and their effects on substances.

In this analysis, we see:

• TlCl_3 , CaO , and CsCl holding ionic bonds, resulting in high boiling points due to strong electrostatic attractions.
• O_2 and CO_2 containing covalent bonds, which generally result in lower boiling points because the covalent bonds within molecules do not necessarily contribute to intermolecular attractions.

The analysis helps predict physical properties by understanding the nature of the chemical bonds present.