The Shape of a Water Molecule

We begin with the Lewis electron dot structures for hydrogen and oxygen atoms. These structures are the following H- and O. Because hydrogen atoms have only one electron, they can form only one chemical bond. Because oxygen atoms have two unpaired electrons, they tend to form two chemical bonds. 

Putting two hydrogen atoms together with one oxygen atom suggests a structure like the following  

If water molecules were linear, water would be nonpolar, and life on Earth would not exist. 

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Water s unique properties are due to the combination of the shape of a water molecule and the ability of water to form multiple hydrogen bonds. 

T, F Because of the bent shape of a water molecule, the dipole... 

The bent shape of a water molecule results in dipoles that do not cancel each other out. The molecule has a net polarity, with the oxygen end being partially negative and the hydrogen ends being partially positive. Refer to Table C-1 in Appendix C for a key to atom color conventions. 

Molecules of compounds are composed of more than one kind of atom. A water molecule consists of two atoms of hydrogen and one atom of oxygen. A molecule of methane consists of one carbon atom and four hydrogen atoms. The shapes of a few molecules are shown in Figure 2-4. 

The shape of a H2O molecule, as determined by VSEPR, is bent because the central oxygen atom has lone pairs of electrons, as shown in Figure 8.23a. Because the polar H—O bonds are asymmetric in a water molecule, the molecule has a definite positive end and a definite negative end. Thus, it is polar. 

Water ammonia and methane share the common feature of an approximately tetra hedral arrangement of four electron pairs Because we describe the shape of a molecule according to the positions of its atoms rather than the disposition of its electron pairs however water is said to be bent and ammonia is trigonal pyramidal... 

Surface tension is the tendency of liquids to reduce their exposed surface to the smallest possible area. A single drop of water - such as a rain drop - tries to take on the shape of a sphere. We attribute this phenomenon to the attractive forces acting between the molecules of the liquid. The molecules within the liquid bulk are attracted equally from all directions, but those near the outer surface of the droplet experience unequal attractions, which cause them to draw in toward the centre of the droplet - a phenomenon experienced as a tension. 

A molecule is considered to be polar, or to have a molecular polarity, when the molecule has an overall imbalance of charge. That is, the molecule has a region with a partial positive charge, and a region with a partial negative charge. Surprisingly, not all molecules with polar bonds are polar molecules. For example, a carbon dioxide molecule has two polar C=0 bonds, but it is not a polar molecule. On the other hand, a water molecule has two polar O—H bonds, and it is a polar molecule. How do you predict whether or not a molecule that contains polar bonds has an overall molecular polarity To determine molecular polarity, you must consider the shape of the molecule and the bond dipoles within the molecule. 

It is common observation that a liquid takes the shape of a container that surrounds or contains it. However, it is also found that, in many cases, there are other subtle properties that arise at the interface of liquids. The most common behavior is bubble and foam formation. Another phenomena is that, when a glass capillary tube is dipped in water, the fluid rises to a given height. It is observed that the narrower the tube, the higher the water rises. The role of liquids and liquid surfaces is important in many everyday natural processes (e.g., oceans, lakes, rivers, raindrops, etc.). Therefore, in these systems, one will expect the surface forces to be important, considering that the oceans cover some 75% of the surface of the earth. Accordingly, there is a need to study surface tension and its effect on surface phenomena in these different systems. This means that the structures of molecules in the bulk phase need to be considered in comparison to those at the surface. 

Each hydrogen atom of a water molecule shares an electron pair with the central oxygen atom. The geometry of the molecule is dictated by the shapes of the outer electron orbitals of the oxygen atom, which are similar to the sp3 bonding orbitals of carbon (see Fig. 

The choice of the cell shape is based on the objective of the study. In studies of water and solution phenomena, a square cell is appropriate because the water molecule is quadravalent to hydrogen bonding to other water molecules or solutes. A water molecule donates two hydrogens and two lone-pair electrons in forming the tetrahedral structure that characterizes the liquid state. The four faces of a square cell thus correspond to the bonding opportunities of a water molecule. 

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