Question

Diagram and label the hydrogen bond between two molecules of hydrogen fluoride, HF.

Short answer

The hydrogen bond in hydrogen fluoride (HF) connects the hydrogen of one HF molecule to the fluorine of another via a dashed line and is characterized by partial charges on the atoms involved.

Step-by-step solution

Understanding Hydrogen Bonding

Hydrogen bonds are a type of weak chemical bond that occurs when a hydrogen atom is attracted to an electronegative atom, such as fluorine, oxygen, or nitrogen. In this case, we will examine the hydrogen bond between two hydrogen fluoride (HF) molecules.

Identifying Bond Components

Each HF molecule consists of a hydrogen atom (H) covalently bonded to a fluorine atom (F). Fluorine is highly electronegative and attracts the shared electron pair, making it partially negative (δ-) and leaving the hydrogen atom partially positive (δ+).

Drawing the HF Molecules

Start by drawing two HF molecules. Represent the first molecule as H-F and the second molecule as H-F. Add partial charges, δ- on the F atoms and δ+ on the H atoms to indicate their charge separations.

Positioning the Molecules Correctly

Align the two molecules such that the hydrogen atom of one HF molecule is near the fluorine atom of the second HF molecule. This setup is necessary for forming a hydrogen bond.

Drawing the Hydrogen Bond

Draw a dashed line between the hydrogen atom of the first HF molecule and the fluorine atom of the second HF molecule. This dashed line represents the hydrogen bond and is typically weaker than the covalent bonds within the molecules.

Labelling the Diagram

Label each part of the diagram clearly. Indicate which lines represent covalent bonds and which represent the hydrogen bond. Note the partial charges δ+ and δ- on the respective atoms to emphasize the polarization in the molecules.

Key concepts

Hydrogen Fluoride

Hydrogen fluoride (HF) is a chemical compound made up of hydrogen and fluorine atoms. In the HF molecule, the hydrogen atom and the fluorine atom are bonded together by a covalent bond, where they share a pair of electrons. HF is a unique compound because of the highly electronegative nature of fluorine. Electronegativity refers to an atom's ability to attract and hold onto electrons.
Fluorine is the most electronegative element, so in HF, it pulls the shared electrons closer to itself, leading to a separation of charge within the molecule. As a result, the fluorine atom carries a partial negative charge (denoted as δ-) and the hydrogen atom carries a partial positive charge (denoted as δ+). This charge separation means that HF molecules interact with each other through hydrogen bonding, where the positive hydrogen of one molecule is attracted to the negative fluorine of another molecule.

Partial Charges

Partial charges are essential in understanding how molecules like HF interact with each other. They arise when electrons in a covalent bond are not shared equally between the atoms. This inequality in electron sharing occurs because atoms in the bond have different electronegativities.

In the case of hydrogen fluoride, the fluorine atom is much more electronegative than the hydrogen atom. This means that the shared electrons in the covalent bond spend more time closer to the fluorine atom. As a result, this unequal sharing creates a dipole: a molecule with a positive and a negative pole. The hydrogen atom becomes partially positive, represented as δ+, while the fluorine atom becomes partially negative, represented as δ-.

• Partial charges play a significant role in intermolecular attractions.
• They lead to hydrogen bonding between molecules, which is crucial for determining the physical properties of substances like boiling and melting points.

Understanding partial charges helps in predicting how molecules behave and interact with other substances.

Covalent Bonds

Covalent bonds are a kind of chemical bond where two atoms share a pair of electrons. This type of bonding is a fundamental concept in chemistry, particularly when looking at molecular compounds like hydrogen fluoride. In HF, the hydrogen and fluorine share electrons to attain stability, resulting in a covalent bond.

The sharing of electrons between atoms allows them to fill their outer electron shell, satisfying the octet rule for most non-metals, essentially reaching a more stable, lower energy state. However, not all covalent bonds are equal. The difference in electronegativity between bonded atoms, like in HF, can cause a polar covalent bond.

• In polar covalent bonds, such as in HF, there is an unequal sharing of electrons.
• This creates a dipole with partial positive and negative charges at either end of the bond.
• Such polarization is what enables the formation of hydrogen bonds between molecules.

Comprehending covalent bonds provides a foundation for studying molecular interactions and properties, illustrating how atoms combine and affect each other's chemical behavior.