Water forms what kind of bonds

Notice that the hydrogen bond shown by the dashed green line is somewhat longer than the covalent O—H bond. It is also much weaker , about 23 kJ mol —1 compared to the O—H covalent bond strength of kJ mol —1. Forty-one anomalies of water" — some of them rather esoteric. Water has long been known to exhibit many physical properties that distinguish it from other small molecules of comparable mass.

Although chemists refer to these as the "anomalous" properties of water, they are by no means mysterious; all are entirely predictable consequences of the way the size and nuclear charge of the oxygen atom conspire to distort the electronic charge clouds of the atoms of other elements when these are chemically bonded to the oxygen. The most apparent peculiarity of water is its very high boiling point for such a light molecule. As you can see from this diagram, extrapolation of the boiling points of the various Group 16 hydrogen compounds to H 2 O suggests that this substance should be a gas under normal conditions.

Compared to most other liquids, water also has a high surface tension. Have you ever watched an insect walk across the surface of a pond? The water strider takes advantage of the fact that the water surface acts like an elastic film that resists deformation when a small weight is placed on it.

If you are careful, you can also "float" a small paper clip or steel staple on the surface of water in a cup. This is all due to the surface tension of the water. A molecule within the bulk of a liquid experiences attractions to neighboring molecules in all directions, but since these average out to zero, there is no net force on the molecule.

For a molecule that finds itself at the surface, the situation is quite different; it experiences forces only sideways and downward, and this is what creates the stretched-membrane effect.

The distinction between molecules located at the surface and those deep inside is especially prominent in H 2 O, owing to the strong hydrogen-bonding forces. The difference between the forces experienced by a molecule at the surface and one in the bulk liquid gives rise to the liquid's surface tension. This drawing highlights two H 2 O molecules, one at the surface, and the other in the bulk of the liquid. As a consequence, a molecule at the surface will tend to be drawn into the bulk of the liquid.

But since there must always be some surface, the overall effect is to minimize the surface area of a liquid. The geometric shape that has the smallest ratio of surface area to volume is the sphere , so very small quantities of liquids tend to form spherical drops. As the drops get bigger, their weight deforms them into the typical tear shape.

The most energetically favorable configuration of H 2 O molecules is one in which each molecule is hydrogen-bonded to four neighboring molecules. Owing to the thermal motions described above, this ideal is never achieved in the liquid, but when water freezes to ice, the molecules settle into exactly this kind of an arrangement in the ice crystal. This arrangement requires that the molecules be somewhat farther apart then would otherwise be the case; as a consequence, ice, in which hydrogen bonding is at its maximum, has a more open structure, and thus a lower density than water.

Here are three-dimensional views of a typical local structure of water left and ice right. Notice the greater openness of the ice structure which is necessary to ensure the strongest degree of hydrogen bonding in a uniform, extended crystal lattice.

The more crowded and jumbled arrangement in liquid water can be sustained only by the greater amount of thermal energy available above the freezing point. When ice melts, the more vigorous thermal motion disrupts much of the hydrogen-bonded structure, allowing the molecules to pack more closely. Water is thus one of the very few substances whose solid form has a lower density than the liquid at the freezing point.

Localized clusters of hydrogen bonds still remain, however; these are continually breaking and reforming as the thermal motions jiggle and shove the individual molecules. As the temperature of the water is raised above freezing, the extent and lifetimes of these clusters diminish, so the density of the water increases. At higher temperatures, another effect, common to all substances, begins to dominate: as the temperature increases, so does the amplitude of thermal motions.

This more vigorous jostling causes the average distance between the molecules to increase, reducing the density of the liquid; this is ordinary thermal expansion.

Because the two competing effects hydrogen bonding at low temperatures and thermal expansion at higher temperatures both lead to a decrease in density, it follows that there must be some temperature at which the density of water passes through a maximum.

The nature of liquid water and how the H 2 O molecules within it are organized and interact are questions that have attracted the interest of chemists for many years. Billions of years ago, it offered an excellent solvent and a truly comfortable environment encouraging growth of all the primitive life forms -- a process that continues to this day. However, scientists had very little idea how hydrogen and oxygen came together and then stayed united to form water h 2 o till researchers, from Lucent Technologies Bell Labs, usa , Steacle Institute for Molecular Sciences in Ottawa, Canada, and the European Synchrotron Radiation Facility esrf in Grenoble, France, discovered water's enduring secret.

Their experimental confirmation of a very controversial quantum mechanics prediction will have a profound impact not only on our understanding of the nature of the water, but other organic molecules like the Deoxyribose Nucleic Acid dna too. The conventional picture of the water molecule comprises two kinds of dissimilar bonds holding the atoms of hydrogen and oxygen firmly.

The hydrogen and oxygen atoms share an electron each, thus forming what is known as a covalent or a sigma bond.

However, the sharing is not equal and the oxygen atoms attract the electron pair with much greater force, leaving the hydrogen nucleus with a net positive charge.

It is this feature that makes water such an excellent solvent. In a molecule of water, the negatively-charged electron cloud of neighbouring oxygen atom attracts the hydrogen atoms. As a result, weak hydrogen bonds are formed where no electrons are shared. This conventional picture was later modified by Nobel Prize winning chemist Linus Pauling in the s.

Using the-then newly developed quantum mechanics machinery, Pauling proved that the conventional picture was wrong. We call this climbing tendency of water capillarity also called capillary action. You saw capillarity in Activity 2 when you placed glass tubing in water. Capillarity starts when the water molecules nearest the wall of the tube are attracted to the tube more strongly than to other water molecules. The water molecules nearest the glass wall of the tube rise up the side adhesion , dragging other water molecules with them cohesion.

Water level in the tube rises until the downward force of gravity becomes equal to than the adhesion and cohesion of water. In a narrow tube, the molecules at the edges have fewer other water molecules to drag up the tube than in a large tube. Therefore, water can rise higher in a narrow tube than in a wider tube see Fig. Capillarity happens naturally in soils, fabric, and wherever there are small spaces that liquids can move through.

Further Investigations. Activity: Cohesion and Adhesion. Special Features:. Representative Image:. Further Investigations: What is an Invertebrate? Question Set: What is a Mammal? Further Investigations: What is a Mammal? Share and Connect. We invite you to share your thoughts, ask for help or read what other educators have to say by joining our community. Partner Organizations. Professional Development. Covalent bonds occur when two atoms—in this case oxygen and hydrogen—share electrons with each other.

Because oxygen and hydrogen attract the shared electrons unequally, each end of the V-shaped H 2 O molecule adopts a slightly different charge.