PROPERTIES OF MATTER 



29 



niok'dilar Iokcs oI aiLiaction binding the subuniLs together. These 

 forces are beHe\etl to be electrical in character and arise from the 

 iinsymmetrical structure of the individual molecule. The three atoms 

 of water do not lie along a line. Rather they form an angle of 105° 

 with the oxygen atom at the point of the angle. In addition to this 

 effect, oxygen is relatively more electronegative than hydrogen; that is, 

 the electrons of the bond between hydrogen and oxygen are displaced 

 slightly toward the latter. In turn this shift causes a slight imbalance 

 in the electrical charge on the molecule. Thus the oxygen is slightly 

 negative and the hydrogen atoms relatively positive. Such separation 

 causes the molecule to act like a miniature magnet, and, like magnets, 

 molecules of this type attract each other and associate as suggested for 

 water. In Figure 2-3 signifies a very small positive charge, © a 

 small negative charge of twice the size, and the dotted lines suggest 

 the interactions leading to aggregation. These attractions, termed 

 hydrogen bonding, are weak compared to the ordinary bonds between 

 hydrogen and oxygen and break and re-form rapidly and continuously 

 in the liquid. 



The slight separation of charges characteristic of certain molecules 

 is called a dipole, and these molecules are said to be polar. Whenever 

 dipoles exist they attract one another even though the molecules 



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FIGURE 2-3. A schematic representation of tlie striictare of water. IMesumahlv the 

 lattice is three dimensional instead of two as dra^vn and may extend to an luiknown 

 degree in any direction. 



