Question

Two atoms \(X\) and \(Y\) are non-polar and electrically symmetrical. What type of intermolecular forces of attraction can be developed between them? (a) Dipole-induced dipole forces (b) London forces or dispersion forces (c) Dipole-dipole forces (d) No forces of any kind.

Short answer

The type of intermolecular forces of attraction that can develop between two non-polar and electrically symmetrical atoms are (b) London forces or dispersion forces.

Step-by-step solution

Identify the Type of Atoms

Understand that both atoms X and Y are described as non-polar and electrically symmetrical, meaning the electric charges are distributed so that there is no overall polarity in the molecule.

Understand Intermolecular Forces

Recall the different types of intermolecular forces: dipole-dipole for polar molecules, dipole-induced dipole for interactions between polar and non-polar, London dispersion forces for non-polar molecules, and hydrogen bonding for certain molecules with hydrogen.

Choose the Correct Intermolecular Force

Since X and Y are non-polar and symmetrical, dipole-dipole and dipole-induced dipole forces are not possible. Hydrogen bonding is not applicable here as this type of force is not listed among the options and typically requires polar molecules with hydrogen atoms bound to electronegative elements. Thus, the only viable type of intermolecular force for non-polar atoms is the London dispersion forces.

Key concepts

London Dispersion Forces

When considering non-polar atoms or molecules, like our atoms X and Y, London dispersion forces come into play. These forces are a type of van der Waals force and the weakest form of intermolecular attraction. They arise due to the momentary fluctuations in electron density within an electron cloud.

Even though electrons are distributed evenly in non-polar molecules, the movement of electrons can result in a temporary dipole. The unequal electron distribution at any moment in one molecule can induce a similar temporary dipole in adjacent molecules. This fleeting attraction between temporary dipoles is what we call London dispersion forces.

Significance in Non-Polar Atoms

For non-polar atoms such as X and Y, London dispersion forces are significant as they represent the only type of intermolecular force that can exist between them. Despite being weak individually, cumulatively they help explain the existence of states of matter and phase changes for non-polar substances. In large molecules with more electrons, these forces can become quite substantial.

Non-Polar Molecules

A molecule is considered non-polar when it has a uniform distribution of electrical charge. This means there is no region of the molecule that holds a greater negative or positive charge. Non-polarity typically occurs in molecules where the constituent atoms have similar electronegativities, or in molecules with symmetrical shapes that allow for an even distribution of charge.

Understanding Polarity

Understanding the concept of non-polar molecules is easier when compared to polar molecules, which have a distinct separation of charge resulting in a positive and a negative pole. Non-polar molecules, such as the hydrocarbons or diatomic molecules like H2, N2, and O2, have a lack of significant poles and therefore do not exhibit strong intermolecular forces such as dipole-dipole or hydrogen bonding.

Electrical Symmetry

Electrical symmetry refers to the balanced distribution of electrical charge across a molecule. In our case, atoms X and Y have symmetrical charge distributions, meaning that the charges are spread out evenly and there's no concentration of negative or positive charge in any particular area of the molecule.

Implications of Electrical Symmetry

Being electrically symmetrical generally means that the molecule is non-polar, as is the case with our atoms X and Y. This symmetry results in the inability of the molecule to have a permanent dipole moment, which in turn affects the strength and type of intermolecular forces that the molecule can participate in. It limits the molecule to only engage in London dispersion forces with other molecules, as there's no permanent dipole to facilitate other types of intermolecular attractions.