Question

Sketch a microscopic picture of water and distinguish between intramolecular bonds and intermolecular forces.Which correspond to the bonds we draw in Lewis structures?

Short answer

In a water molecule, the intramolecular bonds are the covalent bonds between the oxygen atom and each hydrogen atom, formed by the sharing of electron pairs. Intermolecular forces in water include hydrogen bonding (strong attraction between hydrogen and oxygen atoms in neighboring molecules) and dipole-dipole interactions (electrostatic interactions between polar molecules). The bonds drawn in Lewis structures are intramolecular bonds, such as the covalent bonds in the water molecule. Intermolecular forces are not typically shown in Lewis structures.

Step-by-step solution

Draw a water molecule (H2O) with its Lewis structure

Begin by drawing a single water molecule. The molecule has one oxygen atom and two hydrogen atoms. In the Lewis structure, we represent this as O with two single bonds to two H atoms. Place two lone pairs of electrons on the oxygen atom as well. Oxygen (O) ↖ ↑ ↗ H H

Explain the intramolecular bond in water (H2O)

Intramolecular bonds are the bonds that occur within a molecule. In the case of water, the intramolecular bond is the covalent bond between the oxygen atom and each hydrogen atom. Covalent bonds are formed when atoms share pairs of electrons. In water, oxygen shares a pair of electrons with each hydrogen atom, forming a single covalent bond with each one.

Explain the intermolecular forces in water

Intermolecular forces are the forces between different molecules. In water, there are two main types of intermolecular forces: hydrogen bonding and dipole-dipole interactions. 1. Hydrogen bonding: This is a strong attraction between a hydrogen atom that is connected to a highly electronegative atom (like oxygen) and another electronegative atom (also oxygen in this case) from a neighboring molecule. In water, the hydrogen atom of one water molecule is attracted to the oxygen atom of a neighboring molecule, forming a hydrogen bond. 2. Dipole-dipole interactions: These are electrostatic interactions between polar molecules, where one end of the molecule has a partial positive charge and the other end has a partial negative charge. In water, the oxygen atom has a partial negative charge, and the hydrogen atoms have partial positive charges. These charges create an attraction between neighboring water molecules.

Identify the correspondence with Lewis structures

The bonds that we draw in Lewis structures are intramolecular bonds. In the case of water, the Lewis structure shows the covalent bonds between the oxygen atom and the hydrogen atoms within the molecule. Intermolecular forces, like hydrogen bonding and dipole-dipole interactions, are not typically shown in Lewis structures.

Key concepts

Intramolecular Bonds

Intramolecular bonds are the forces that hold together the atoms within a molecule. They are the reason why molecules stay intact and are the foundation of molecular structure. In water (\(\text{H}_2\text{O}\)), these bonds are covalent bonds, which occur when oxygen and hydrogen atoms share electrons. Such sharing of electrons occurs in a way that becomes mutually beneficial, allowing for the chemical stability of the molecule.
Intramolecular bonds are crucial because they determine the chemical properties of a substance. These bonds involve the allocation of electrons between atoms, resulting in a stable electronic arrangement. Moreover, the strength of intramolecular bonds dictates how much energy is required to break them, impacting the substance's boiling and melting points. In summary, understanding intramolecular bonds gives insight into the very fabric of chemical compounds, influencing how they react with other substances and retain their structure.
Covalent bonds are a specific type of intramolecular bond found in many compounds, including water.

Covalent Bonds

Covalent bonds form when two atoms share one or more pairs of electrons. This can be thought of as a "give-and-take" interaction where both atoms benefit from shared access to electrons. In the case of water, a covalent bond exists between the oxygen atom and each of the two hydrogen atoms . This is represented through shared electron pairs, ensuring each hydrogen obtains access to the oxygen's higher electronegative pull.

• Covalent bonds can be either polar or nonpolar.
  In polar covalent bonds like in water, the electron pair is not shared equally, leading to partial charges.
• Nonpolar covalent bonds involve equal sharing of electrons.

Water’s covalent bonds demonstrate polarity. Here, the oxygen atom is more electronegative than hydrogen, pulling the shared electrons closer and creating a slight charge difference in the molecule. This unequal sharing results in the molecule being polar, which is why water exhibits unique properties such as high surface tension and solvent capability. Covalent bonds represent the basic building blocks in molecular chemistry, key for understanding how different atoms connect to form stable frameworks.

Lewis Structures

Lewis structures are diagrams that show the bonds between atoms within a molecule and any lone pairs of electrons that may exist. They are instrumental in visualizing and predicting the behavior of molecules in chemical reactions. For water, the Lewis structure clearly represents the two covalent bonds between oxygen and hydrogen. These structures use dots to symbolize electrons, with lines representing the sharing of electrons (bonds).
Creating a Lewis structure involves:

• Identifying the valence electrons available for bonding for each element.
• Arranging the electrons to depict bonds, ensuring atoms achieve a filled outer electron shell.
• Minimizing electron pair repulsions to stabilize the molecule’s geometry.

Water’s Lewis structure effectively illustrates the two single covalent bonds and the lone pairs on the oxygen atom. It provides a fundamental visual representation of how the molecule is constructed. Understanding Lewis structures simplifies the process of predicting molecular shapes, bond formation, and reactivity patterns, which are essential skills in the field of chemistry.