Water's bent shape has important implications for its chemical properties. One of these properties is polarity. We need to talk about two types of polarity: bond polarity and molecular polarity. Water exhibits both kinds of polarity. First, the bonds between oxygen and hydrogen are polar because the electrons aren't evenly distributed between the two atoms.
As we see here, they're closer to the oxygen atom than to the hydrogen atom. A polar bond occurs when one atom in the bond is more electronegative than the other.
Electronegativity is the tendency of an atom in a bond to attract shared bonding electrons. The bonds between hydrogen and oxygen are polar because oxygen is more electronegative than hydrogen. Water also exhibits the second kind of polarity. Its bent shape plays an important role in its molecular polarity. Let's look again at the linear depiction of the water molecule. If the molecule were linear rather than bent, the electron distribution would be even, not uneven, so the molecule would NOT be polar.
Another way to think of this is that the "pull" of the electrons toward the oxygen from the bond on the left will be cancelled out by the "pull" of the electrons from the bond on the right. Without a net "pull" in any direction, the molecule won't be polar. We already know the electrons in the two bonds are shifted toward the oxygen atom. More importantly, the two unshared electron pairs on oxygen mean that one region of the molecule has more electron density than the rest of the molecule.
By definition the water molecule is polar, since there's an uneven distribution of electron density. We sometimes indicate the electron distribution by putting a partial positive charge, designated delta-plus, on the hydrogen atoms and a partial negative charge, designated delta-minus, on the oxygen. The polar structure of water has important consequences for the interactions that occur between water molecules in biological systems.
The most important interaction between water molecules is hydrogen bonding. Recall that a hydrogen bond is a weak to moderate attractive force between a hydrogen atom bonded to oxygen, nitrogen, or fluorine, and an oxygen, nitrogen or fluorine atom on another molecule. Hydrogen bonds are usually represented by dotted lines. A hydrogen atom, at the partially positive end of the molecule, interacts with the partially negative oxygen atom on another water molecule.
The polar bonds do not point in opposite directions, though, and this is why water is polar. Water is a polar molecule. The reason for this anomaly lies in the unusual properties of the water molecule H2O. Its oxygen atom O and the two hydrogen atoms H are asymmetrically arranged. This produces a dipole, a molecule with one negatively and one positively charged end. A water molecule is not linear because of the electron structure of the oxygen atoms in the water molecules. Its configuration is 1s2 2s2 2p4.
Because of this configuration oxygen has two electron pairs and two single valence electrons. In water, the oxygen atom has two lone pairs. These two lone pairs repel the hydrogen-oxygen bonded pairs so much that the molecule is at its lowest energy arrangement when the H-O-H bond angle is As a result, the water molecule can be classified as non-linear. It is 3 atoms total. This is tetrahedral electron pair geometry.
The 2 lone electron pairs exerts a little extra repulsion on the two bonding hydrogen atoms to create a slight compression to a o bond angle. The water molecule is bent molecular geometry because the lone electron pairs, although still exerting influence on the shape, are invisible when looking at molecular geometry.
The molecule is two dimensional and bent as opposed to the beryllium hydride case which was a linear or straight line molecular geometry because it did not have a lone electron pair. In this example, O 3 , the Lewis diagram shows O at the center with one lone electron pair and two other oxygen atoms attached. This shows trigonal planar for the electron pair geometry and and bent the molecular geometry.
The one lone electron pair exerts a little extra repulsion on the two bonding oxygen atoms to create a slight compression to a o bond angle from the ideal of o. Compare it to the BeH 2 which has 2 hydrogen atoms and no lone electron pairs. Ozone is a protective molecule by absorbing UV radiation when high in the stratosphere. However when close to the surface, ozone is produced as part of photochemical smog air pollution and is a powerful lung irritant.
Nitrogen Dioxide:. In this example, NO 2 , the Lewis diagram shows nitrogen at the center with one lone electron.
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