Compounds and Chemical Bonds

Many of us have a bottle in our medicine cabinet containing a mild disinfectant consisting of hydrogen peroxide and water. The liquid is about 3% hydrogen peroxide, H2O2, and about 97% water. Classify each of the following as a pure substance or a mixture. If it is a pure substance, is it an element or a compound  

Let s first consider the compound hydrogen chloride, HCl. When HCl is dissolved in water, the resulting mixtiu e is called hydrochloric acid. Not only is this mixture a very common laboratory agent, hut it is also used in food processing and to treat the water in swimming pools. 

When the electrons of a covalent bond are shared unequally, the bond is called a polar covalent bond. Due to the unequal sharing of the electrons in the bond, a polar covalent bond has one atom with a partial positive charge, 5+, and one atom with a partial negative charge, 5-. 

Electrons shift toward the chlorine atom, forming partial plus and minus charges. 

In contrast to sodium, chlorine readily gains an extra electron forming an anion, Cl. Again, there is a noticeable difference between the ion and the atom of chlorine. The table salt we discussed above is sodium chloride, which contains chloride anions. Just like sodium, these chloride ions are present in French fries or any other salted foods. Chlorine atoms, on the other hand, combine in pairs to form a yellowish-green gas, CI2, which irritates the lungs and can be toxic. The behavior of the ion is clearly much different from that of the neutral atom or molecule. 

Polymers do not generally contain ions. But ions are important in the chemical reactions used to produce many common plastics. As a result of their electric charge, ions are often much more reactive than neutral atoms or molecules. So small amounts of ions are often used to initiate or sustain the chemical reactions that join monomers together to form polymers. 

Chlorine gas released in a January 2005 train accident in South Carolina led to eight deaths and forced many residents from their homes for days. 

---

Chemical compounds and chemical bonds have aheacfy been mentioned several times in this book. It is not possible to even begin the study of chemistry without some knowledge of compounds and bonding, because they are the essence of chemical science. Tlie first three chapters have provided an overview of chemistry, a discussion of the properties of matter, and an explanation of atoms and elements. With this background, it is now possible to discuss chemical bonds, molecules, and compounds in more detail. 

Compounds and chemical bonds are formed by sharing electrons. Atoms or atom groups with excess electrons (+ valence) share those with atoms or atom groups having an electron deficiency (- valence). 

---