Molecular nitrogen consists of two nitrogen atoms triple bonded to each other and, as with all molecules, the sharing of these three pairs of electrons between the two nitrogen atoms allows for the filling of their outer electron shells, making the molecule more stable than the individual nitrogen atoms.
This strong triple bond makes it difficult for living systems to break apart this nitrogen in order to use it as constituents of proteins and DNA. The formation of water molecules provides an example of covalent bonding. The hydrogen and oxygen atoms that combine to form water molecules are bound together by covalent bonds.
The electron from the hydrogen splits its time between the incomplete outer shell of the hydrogen atoms and the incomplete outer shell of the oxygen atoms.
To completely fill the outer shell of oxygen, which has six electrons in its outer shell but which would be more stable with eight, two electrons one from each hydrogen atom are needed: hence the well-known formula H 2 O.
The electrons are shared between the two elements to fill the outer shell of each, making both elements more stable. There are two types of covalent bonds: polar and nonpolar. In a polar covalent bond , shown in Figure 1, the electrons are unequally shared by the atoms and are attracted more to one nucleus than the other.
This partial charge is an important property of water and accounts for many of its characteristics. Water is a polar molecule, with the hydrogen atoms acquiring a partial positive charge and the oxygen a partial negative charge. Thus oxygen has a higher electronegativity than hydrogen and the shared electrons spend more time in the vicinity of the oxygen nucleus than they do near the nucleus of the hydrogen atoms, giving the atoms of oxygen and hydrogen slightly negative and positive charges, respectively.
Another way of stating this is that the probability of finding a shared electron near an oxygen nucleus is more likely than finding it near a hydrogen nucleus. Hydrogen bonds, which are discussed in detail below, are weak bonds between slightly positively charged hydrogen atoms to slightly negatively charged atoms in other molecules. Other covalently bonded molecules, like hydrogen fluoride gas HF , do not share electrons equally.
The fluorine atom acts as a slightly stronger puppy that pulls a bit harder on the shared electrons see Fig. Even though the electrons in hydrogen fluoride are shared, the fluorine side of a water molecule pulls harder on the negatively charged shared electrons and becomes negatively charged. The hydrogen atom has a slightly positively charge because it cannot hold as tightly to the negative electron bones.
Covalent molecules with this type of uneven charge distribution are polar. Molecules with polar covalent bonds have a positive and negative side. In this analogy, each puppy represents an atom and each bone represents an electron. Water H2O , like hydrogen fluoride HF , is a polar covalent molecule.
When you look at a diagram of water see Fig. The unequal sharing of electrons between the atoms and the unsymmetrical shape of the molecule means that a water molecule has two poles - a positive charge on the hydrogen pole side and a negative charge on the oxygen pole side. We say that the water molecule is electrically polar. Each diagram shows the unsymmetrical shape of the water molecule.
In part c , the polar covalent bonds are shown as electron dots shared by the oxygen and hydrogen atoms. In part d , the diagram shows the relative size of the atoms, and the bonds are represented by the touching of the atoms. The polar covalent bonding of hydrogen and oxygen in water results in interesting behavior, suc. Water is attracted by positive and by negative electrostatic forces because the liquid polar covalent water molecules are able to move around so they can orient themselves in the presence of an electrostatic force.
Although we cannot see the individual molecules, we can infer from our observations that in the presence of a negative charge, water molecules turn so that their positive hydrogen poles face a negatively charged object. The same would be true in the presence of a positively charged object; the water molecules turn so that the negative oxygen poles face the positive object.
See Fig. The difference in the two runs depends on the nature of the hydrogen bonds. If they were purely electrostatic, with no sigma bonds being shared, then both orientations have identical results. However, the results were different, thus confirming the quantum mechanical result that electrons in the hydrogen bonds are shared with the neighbouring molecules. The experimental confirmation of the nature of the hydrogen bond in water will lead to a better understanding of the water's mysterious properties, many of which are not completely understood even today.
For instance, water is one of the few liquids that expand on freezing. The hydrogen bond is present in many biological molecules. Maybe one day, we will understand why and how life originated on our planet from more information obtained about the nature of the hydrogen bond Physical Review Letters , January We are a voice to you; you have been a support to us.
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