Question

Formaldehyde has the formula \(\mathrm{CH}_{2} \mathrm{O},\) where \(\mathrm{C}\) is the central atom. The molecules in a sample of formaldehyde are attracted to each other by a combination of a. dipole-dipole forces and ionic forces. b. hydrogen bonding and dipole-dipole forces. c. ionic forces and hydrogen bonding. d. London dispersion forces and hydrogen bonding. e. dipole-dipole forces and London dispersion forces.

Short answer

In formaldehyde \(\mathrm{CH}_2\mathrm{O}\), ionic forces and hydrogen bonding are not present. However, the molecule's polar nature results in the presence of dipole-dipole forces, and the inherently occurring London dispersion forces are also present. Therefore, the correct answer is (e) dipole-dipole forces and London dispersion forces.

Step-by-step solution

Formaldehyde has the chemical formula \(\mathrm{CH}_2\mathrm{O}\). The molecule is a trigonal planar structure, with the less electronegative carbon atom as the central atom. Carbon forms a double bond with the oxygen atom and single bonds to the two hydrogen atoms. #2. Evaluate possibility of ionic forces #

Ionic forces are typically observed in ionic compounds, which consist of positively and negatively charged ions. Formaldehyde is a covalent compound, and there are no charged ions present, indicating that there are no ionic forces. #3. Evaluate the possibility of hydrogen bonding#

Hydrogen bonding is a specific type of intermolecular force that exists when a hydrogen atom is bonded to a highly electronegative atom like fluorine, oxygen, or nitrogen. In formaldehyde, hydrogen atoms are bonded to a carbon atom, which is less electronegative than oxygen and nitrogen. Thus, hydrogen bonding is not present in formaldehyde. #4. Evaluate the possibility of dipole-dipole forces#

Dipole-dipole forces occur between polar molecules, due to the electrostatic attraction between the partially positive and partially negative charged atoms within the molecules. In formaldehyde, the uneven distribution of electron density results in a polar molecule with a partial positive charge on the carbon and hydrogen atoms and a partial negative charge on the oxygen atom. This leads to the presence of dipole-dipole forces between the formaldehyde molecules. #5. Evaluate the possibility of London dispersion forces#

London dispersion forces, or induced dipole forces, are weak intermolecular forces that are present in all molecules, whether they are polar or nonpolar. These forces arise due to temporally induced dipoles in the electron distributions of the interacting atoms or molecules. London dispersion forces will therefore be present in formaldehyde as well. #Conclusion#

Based on the above analysis, formaldehyde exhibits dipole-dipole forces and London dispersion forces. The correct answer is (e) dipole-dipole forces and London dispersion forces.

Key concepts

Dipole-Dipole Forces

Dipole-dipole forces occur in polar molecules. These forces arise due to the electrostatic attraction between the positive and negative ends of the dipoles. In a polar molecule like formaldehyde,

• Oxygen, being more electronegative, pulls electron density towards itself, creating a partial negative charge.
• Conversely, the carbon and hydrogen atoms have a partial positive charge.

This difference in charge allows molecules to attract each other, forming dipole-dipole interactions. These interactions are critical in many chemical processes and can heavily influence a substance's boiling and melting points.
By understanding dipole-dipole forces, we can predict the behavior of polar molecules under various conditions, making it easier to grasp why substances mix or repel each other.

London Dispersion Forces

London dispersion forces, also known as induced dipole forces, are present in all molecules. They are the weakest intermolecular forces and occur due to temporary dipoles created when electrons move around a nucleus.

• These forces increase with the number of electrons in a molecule or atom.
• Even nonpolar molecules experience dispersion forces.

In formaldehyde, London dispersion forces occur alongside dipole-dipole forces, providing secondary interactions between the molecules.
Despite being weak, these forces become significant in larger molecules and contribute to the overall stability and physical properties of the substance.

Formaldehyde Structure

The chemical structure of formaldehyde is \(\mathrm{CH}_2\mathrm{O},\)with carbon as the central atom, forming a trigonal planar shape.

• The carbon atom forms two single bonds with hydrogen atoms and one double bond with the oxygen atom.
• This geometry allows for an efficient distribution of electron density.

The structure's polarity is due to the presence of the highly electronegative oxygen, which creates a dipole moment. This causes formaldehyde to have unique physical and chemical properties.
Recognizing this structure helps in understanding its reactivity and interaction with other molecules.

Hydrogen Bonding

Hydrogen bonding is a special type of intermolecular force, notably strong and prevalent when hydrogen is bonded to nitrogen, oxygen, or fluorine.

• This bond creates a very polar situation, as these elements have high electronegativity.
• Hydrogen bonds can significantly impact the boiling and melting points of compounds.

In formaldehyde, hydrogen is bonded to carbon, not to the more electronegative oxygen, eliminating the possibility of hydrogen bonding within this molecule.
Understanding what qualifies as hydrogen bonding is crucial in predicting a substance's physical behaviors.

Covalent Compounds

Covalent compounds are formed by the sharing of electrons between non-metal atoms.

• Unlike ionic compounds, they do not contain charged ions but neutral molecules.
• This sharing of electrons allows for various bond strengths and types.

Formaldehyde is a perfect example, where electrons are shared among carbon, hydrogen, and oxygen atoms, resulting in a stable structure.
The nature of covalent bonding leads to specific properties, such as lower melting and boiling points compared to ionic compounds.
Understanding covalent compounds is essential for grasping how different molecules behave and interact in a chemical context.