How many hydrogen bonds can a water molecule form?

Water (H2O) is one of the most important molecules on Earth. It is vital for all known forms of life and plays a critical role in many chemical and physical processes. A key property of water is its ability to form hydrogen bonds. But how many hydrogen bonds can a single water molecule form? This article provides a deep dive into the hydrogen bonding capabilities of water.

Quick Answer

A single water molecule can form a maximum of four hydrogen bonds – two as a hydrogen bond donor and two as a hydrogen bond acceptor. This capability allows water to form extensive hydrogen bonding networks in liquid and solid states.

What is a Hydrogen Bond?

A hydrogen bond is an attractive force between a hydrogen atom bonded to a highly electronegative atom and another nearby highly electronegative atom. The hydrogen atom serves as a “bridge” between the two electronegative atoms.

In water, the electronegative oxygen atom has a partial negative charge while the hydrogen atoms have a partial positive charge. This charge difference allows the hydrogen atoms to be electrostatically attracted to the oxygen atoms of nearby water molecules.

Hydrogen bonds are weaker than covalent and ionic bonds. But collectively, hydrogen bonds have a major influence on the properties of water and other compounds.

Hydrogen Bond Donors and Acceptors

In the context of hydrogen bonding, molecules can act as hydrogen bond “donors” and/or “acceptors”.

A hydrogen bond donor contains a hydrogen atom that is covalently bonded to an electronegative atom like oxygen, nitrogen, or fluorine. This hydrogen atom has a partial positive charge and can form a hydrogen bond by electrostatically attracting a nearby electronegative atom.

A hydrogen bond acceptor contains an electronegative atom with a lone pair of electrons. This lone pair has a partial negative charge and can attract a partially positively charged hydrogen atom on another molecule, forming a hydrogen bond.

Water as a Hydrogen Bond Donor and Acceptor

A single water molecule contains two hydrogen atoms bonded to an oxygen atom. The oxygen atom has two lone pairs of electrons.

This configuration allows a water molecule to act as both a hydrogen bond donor through its hydrogen atoms AND a hydrogen bond acceptor through its lone pairs. This dual capability enables extensive hydrogen bonding between water molecules.

Water as a Hydrogen Bond Donor

As a hydrogen bond donor, a water molecule can form two hydrogen bonds through its two O-H covalent bonds. The hydrogen atoms have partial positive charges and can electrostatically interact with lone pairs on nearby water molecules.

Water as a Hydrogen Bond Acceptor

As a hydrogen bond acceptor, a water molecule can form two hydrogen bonds by using its two lone pairs. The lone pairs have partial negative charges and can attract the partially positively charged hydrogens on nearby water molecules.

How Many Hydrogen Bonds Can a Single Water Molecule Form?

By combining its dual hydrogen bonding capabilities, a single water molecule can form a maximum of four hydrogen bonds at any given time – two as a hydrogen bond donor through its hydrogen atoms, and two as a hydrogen bond acceptor through its lone pairs.

Bond Type # Bonds
As hydrogen bond donor 2
As hydrogen bond acceptor 2
Total bonds 4

This four-hydrogen bond arrangement allows water to form tetrahedral coordination with four neighboring water molecules. The extensive hydrogen bonding network profoundly impacts the unique properties of liquid water and ice.

Hydrogen Bonding in Liquid Water

In liquid water, the water molecules are constantly moving and colliding. The hydrogen bonding pattern is continuously breaking and reforming.

At any instant, an average water molecule in the liquid forms 2.4 hydrogen bonds with surrounding molecules. Some molecules may form the maximum 4 bonds, while others have fewer or even no bonds at a given moment.

The continuous making and breaking of hydrogen bonds contributes to water’s ability to flow as a liquid at relatively high temperatures. It also allows water to retain heat and dissolve other substances well.

Hydrogen Bonding in Ice

In ice, the average water molecule forms about 3.4 hydrogen bonds with its neighbors. This more extensive hydrogen bonding network rigidly locks the molecules into a crystalline structure.

This solid framework is why ice is less dense than liquid water and has such a high melting point compared to other molecules of similar size. The hydrogen bonds have to be broken for ice to become liquid.

Other Interesting Facts About Water’s Hydrogen Bonds

Here are a few other fascinating facts about hydrogen bonding in water:

– Hydrogen bond strength in water is estimated to be 5–10 kcal/mol. This is less than 5% the strength of an average O-H covalent bond.

– Water has one of the highest known hydrogen bonding abilities of any molecule. Only hydrogen fluoride has higher measured hydrogen bond strengths.

– The number of nearest neighbors for a water molecule in ice is 4. In liquid water, the number of nearest neighbors is reduced to about 3.4.

– High temperatures and pressures can break hydrogen bonds and enable water molecules to get closer than normal. This allows liquid water to become denser than ice.

– Water can form both intermolecular hydrogen bonds with other water molecules and intramolecular bonds between the hydrogen and oxygen within the same molecule. Intramolecular bonding makes isolated water molecules more stable.


A single water molecule has the potential to form a maximum of four hydrogen bonds – two using its hydrogen atoms and two using its lone electron pairs. This versatile hydrogen bonding enables water to form dynamic, three-dimensional networks with itself in liquid and solid states. Hydrogen bonding explains many of the emergent properties of water that are critical to sustaining life on Earth. Ongoing research continues to reveal new insights into how hydrogen bonding allows water molecules interact in complex ways.

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