Characteristics of Hydrogen Bonds and Examples

Hydrogen bonds are the attraction between two atoms that have participated in other chemical bonds. One atom is hydrogen, while the other can be an electronegative atom, such as oxygen, chlorine, or fluorine. Hydrogen bonds can be formed between atoms in a molecule or between two separate molecules. Hydrogen bonds are weaker than ionic bonds or covalent bonds , but stronger than van der Waals forces. This is also one of the characteristics or characteristics of hydrogen bonds.

Hydrogen bonds play an important role in biochemistry and produce many unique properties of water. Examples of hydrogen bonds such as hydrogen bonds in water, hydrogen bonds in polymers , hydrogen bonds in ammonia, and others.

table of contents

  • Hydrogen Bonding
    • Characteristics of Hydrogen Bonding
      • Requirements or conditions for hydrogen bonding
      • Effects of Hydrogen Bonding on Elements
      • Properties of hydrogen bonds
      • Compounds that have hydrogen bonds have high melting and boiling points
      • Hydrogen bond strength
      • Hydrogen bond type
    • Example of a Hydrogen Bond
      • Hydrogen bonding in Hydrogen fluoride
      • Hydrogen Bonding in Water
      • Hydrogen Bonding in Ammonia
      • Hydrogen Bonding in Alcohol
      • Hydrogen Bonding in Polymers
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Hydrogen Bonding

Hydrogen bonding (often abbreviated as H -ond) is an electrostatic attraction between hydrogen atoms (H) that are covalently attached to more electronegative atoms or groups, especially the second line element nitrogen (N), oxygen (O), or fluorine (F) – hydrogen bond donor (Dn) – and other electronegative atoms that carry a pair of free electrons – the hydrogen bond acceptor (Ac).

Such interaction systems are generally denoted by Dn-H ··· Ac, where solid lines show full covalent bonds, and broken lines show hydrogen bonds. The use of three centralized points for hydrogen bonds is specifically recommended by IUPAC.

There is general agreement that there are actually minor covalent components for hydrogen bonds, especially for moderate to strong hydrogen bonds (> 5 kcal / mol), although the importance of covalence in hydrogen bonds is debatable. At the other end of the scale, there is no clear boundary between weak hydrogen bonds and van der Waals interactions (eg, dipoles).

Understanding Hydrogen Bonding

Hydrogen bonds are a type of interesting (dipole-dipole) interaction between electronegative atoms and hydrogen atoms that are bound to other electronegative atoms. This bond always involves the hydrogen atom. Hydrogen bonds can occur between molecules or in parts of one single molecule.

Hydrogen bonds tend to be stronger than van der Waals forces, but weaker than covalent or ionic bonds. This is about 1/20 (5%) of the strength of the covalent bonds formed between OH. However, even this weak bond is strong enough to withstand slight temperature fluctuations.

Understanding Hydrogen Bonding According to Experts

The definition of hydrogen bonds according to experts, among others:

Chemistry Libre Texts

Hydrogen bonding is a type of weak force that forms a special type of dipole-dipole attraction that occurs when a hydrogen atom is attached to a very electronegative atom around another electronegative atom with a free electron pair. These bonds are generally stronger than ordinary dipoles and dispersion forces, but weaker than actual covalent and ionic bonds.

Encyclopedia Britannica

Hydrogen bonds are interactions involving hydrogen atoms that are located between a pair of other atoms which have a high affinity for electrons; such bonds are weaker than ionic bonds or covalent bonds but stronger than van der Waals forces. Hydrogen bonds can exist between atoms in different molecules or in the same molecule.

Sciencing

Hydrogen bonding is a term in the sense of chemical bonds for intermolecular forces caused by strong attraction between parts of molecules with little charge. That happens when a molecule contains an atom which, because of its size, gives a greater pull to the covalent bonds in the molecule.

This results in divided electrons orbiting more than the atom they bind to. This unequal portion of electrons causes the molecule to have positive parts and corresponding negative parts.

Characteristics of Hydrogen Bonding

The following are the characteristics or characteristics of hydrogen bonds, including:

Requirements or conditions for hydrogen bonding

In a molecule, when a hydrogen atom is associated with a very electronegative atom, it attracts more electron pairs so that the end of the molecule becomes slightly negative while the other end becomes slightly positive.

The negative end of one molecule attracts the other positive end and as a result, a weak bond is formed between them. This bond is called a hydrogen bond. As a result of hydrogen bonds, hydrogen atoms connect two electronegative atoms together, one by covalent bonds and the other by hydrogen bonds.

Requirements or conditions for forming hydrogen bonds are:

  1. Molecules must contain highly electronegative atoms connected to hydrogen atoms. The higher the electronegativity, the more polarization of the molecule.
  2. The size of the electronegative atom must be small. The smaller the size, the greater the electrostatic attraction.

Effects of Hydrogen Bonding on Elements

Hydrogen bonds have several effects on the elements, including:

  1. Association: Carboxylic acid molecules exist as dimers due to hydrogen bonds. The molecular mass of the compound was found to be double that calculated from the simple formula. 
  1. Dissociation: In aqueous solution, HF ( Hydrogen fluoride ) dissociates and gives difluoride ions, not fluoride ions. This is due to the hydrogen bonding to HF. HCl, HBr, HI molecules do not form hydrogen bonds. This explains the absence of compounds such as KHCl2, KHBr2, KHI2.

Properties of hydrogen bonds

  1. Solubility: Lower alcohols dissolve in water due to hydrogen bonds that can occur between water molecules and alcohol.
  2. Volatility: Because compounds that involve hydrogen bonds between different molecules have a higher boiling point, so they are less volatile.
  3. Viscosity and surface tension: Substances containing hydrogen bonds exist as related molecules. So their flow becomes relatively difficult. They have higher viscosity and high surface tension.
  4. Lower ice density than water: In the case of solid ice, hydrogen bonds give rise to the structure of water molecules like a cage. In fact, each water molecule is connected tetrahedral with four water molecules.

The molecules are not tightly packed because they are in a liquid state. When the ice melts, this structure collapses and the molecules come closer together. So for the same mass of water, the volume decreases and the density increases. Therefore, ice has a lower density than water at 273 K. That’s why ice floats.

Compounds that have hydrogen bonds have high melting and boiling points

Compounds that have hydrogen bonds show abnormal melting and high boiling points. The high melting and boiling points of compounds containing hydrogen bonds are due to the fact that extra energy is needed to break these bonds.

  1. The high boiling point of hydrogen fluoride between halogen acids is due to hydrogen bonds.
  2. H2O is a liquid while H2S, H2Se and H2Te are all gases at ordinary temperatures. In water, hydrogen bonds cause interconnections in water molecules that produce more boiling points than in other compounds.
  3. Ammonia has a higher boiling point than PH3 because there is a hydrogen bond in NH3 but not PH3.
  4. Ethanol has a higher boiling point than diethyl ether because there is a hydrogen bond in ethanol.

Hydrogen bond strength

Hydrogen bonds have weak strength.

  1. Weak bond strength

Hydrogen bonds are weak bonds. The strength of hydrogen bonds is between the weak van der Waals strength and strong covalent bonds. The energy of dissociation of hydrogen bonds depends on the pull of the pair of electrons distributed and hence on the electronegativity of the atom.

Hydrogen bond type

There are two types of H bonds, and are classified as follows:

  1. Intermolecular Hydrogen Bonding

When hydrogen bonds occur between different molecules of the same or different compounds, it is called hydrogen bonds between molecules. For example – hydrogen bonds in water, alcohol, ammonia and others.

  1. Intramolecular Hydrogen Bonding

The hydrogen bonds that occur within the molecule itself are called intramolecular hydrogen bonds. This occurs in compounds containing two groups so that one group contains hydrogen atoms connected to electronegative atoms and the other group contains highly electronegative atoms associated with lower electronegative atoms than other groups.

A bond is formed between hydrogen atoms from one group and atoms that are more electronegative than another group.

Example of a Hydrogen Bond

Here are some examples of hydrogen bonds, including:

  1. Hydrogen bonding in Hydrogen fluoride

Fluorine has the highest electronegativity value, so it always forms the strongest hydrogen bond.

  1. Hydrogen Bonding in Water

Water molecules contain highly electronegative oxygen atoms that are connected with hydrogen atoms. Oxygen atoms attract more electron pairs together and the ends of these molecules become negative while hydrogen atoms become positive.

  1. Hydrogen Bonding in Ammonia

It contains a very electronegative nitrogen atom which is connected to a hydrogen atom.

  1. Hydrogen Bonding in Alcohol

Alcohol is a type of organic molecule that contains the -OH group. Usually, if there are molecules containing hydrogen atoms connected to oxygen or nitrogen directly, hydrogen bonds are easily formed.

  1. Hydrogen Bonding in Polymers

Hydrogen bonding is an important factor in determining the structure and 3D properties obtained by synthetic and natural proteins. Hydrogen bonds also play an important role in determining the structure of cellulose as well as the properties of polymer derivatives such as cotton or flax.

That was a series of explanations and full review to all readers related to the characteristics of hydrogen bonds and their examples in everyday life. Hopefully, through this material can provide insight and increase knowledge for all readers.

 

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