Question

What are intermolecular forces and how are they different from covalent bonds?

Short answer

Intermolecular forces are weaker forces between molecules, while covalent bonds are strong bonds within molecules involving shared electrons.

Step-by-step solution

Understanding Intermolecular Forces

Intermolecular forces are forces of attraction or repulsion between molecules or ions. They are responsible for many physical properties of substances, such as boiling points, melting points, and solubilities.

Types of Intermolecular Forces

There are three main types of intermolecular forces: Van der Waals forces (including London dispersion forces), dipole-dipole interactions, and hydrogen bonds. Each type varies in strength and specific conditions under which they occur.

Definition of Covalent Bonds

Covalent bonds are a type of chemical bond where pairs of electrons are shared between atoms. These bonds result in the formation of molecules.

Comparing Intermolecular Forces to Covalent Bonds

Intermolecular forces are generally much weaker than covalent bonds. While covalent bonds involve the sharing of electrons between atoms within a molecule, intermolecular forces describe how different molecules attract or repel each other.

Physical Properties

Intermolecular forces affect physical properties such as boiling and melting points, whereas covalent bonds determine the chemical structure and identity of the molecule.

Key concepts

Van der Waals Forces

Van der Waals forces are a type of intermolecular force that includes London dispersion forces, dipole-dipole interactions, and dipole-induced dipole interactions. These forces are usually weak and temporary, but they play an important role in the behavior of molecules, especially non-polar ones.

• **London Dispersion Forces:** These are the weakest of the Van der Waals forces. They arise due to temporary fluctuations in electron distribution within molecules, creating temporary dipoles. London dispersion forces are present in all molecules, whether polar or non-polar.

• **Dipole-Dipole Interactions:** These occur between molecules that have permanent dipoles. A positive end of one polar molecule is attracted to the negative end of another polar molecule.

• **Dipole-Induced Dipole Interactions:** These happen when a polar molecule induces a dipole in a non-polar molecule.

Van der Waals forces are responsible for the condensation of gases into liquids and the solidity of molecular structures at low temperatures.

Covalent Bonds

Covalent bonds are strong, lasting bonds where two atoms share pairs of electrons. These bonds form between non-metal atoms with similar electronegativities. The sharing of electrons allows each atom to attain the electron configuration of a noble gas, achieving stability.

Covalent bonds are directional, meaning the atoms follow specific paths in space to overlap with each other and share electrons.
For example,
\(\text{H}_2\text{O}\)
\(\text{H}_2\text{O}_2\text{C}\)
\(\text{CH}_4\text{H}\text{C}\)
Each keeps its individual electrons, forming a molecule which is neutral overall.

Covalent bonds can be:
• **Single Bonds:** Involve one pair of shared electrons.
• **Double Bonds:** Involve two pairs of shared electrons.
• **Triple Bonds:** Involve three pairs of shared electrons.

These bonds define the structure and reactivity of a molecule.
Covalent bonds determine the chemical identity of the compounds and are generally stronger than intermolecular forces, which influence the physical properties of substances.

Hydrogen Bonds

Hydrogen bonds are a special type of strong dipole-dipole interaction that involve a hydrogen atom bonded to a highly electronegative atom like nitrogen, oxygen, or fluorine.

When these atoms covalently bond to hydrogen, they attract the shared electrons more strongly, giving the hydrogen a partial positive charge
(\(\text{\text{δ}}^{+}\)\text{\(\text{H}_2\text{O}_2\text{C}\)\(C-H\)} (Conversely, the electronegative atom) and the electronegative atom (\(\))\(δ^{-}\))

The result is hydrogen bonds are responsible for many unique properties of water, including its high boiling point relative to its molecular weight.

Hydrogen bonds also stabilize DNA through the pairing of nitrogenous bases and help proteins maintain their structure.

Although stronger than Van der Waals forces, hydrogen bonds are weaker than covalent bonds.
Hydrogen bonding is significant in biological systems and is key to the structure and function of macromolecules.