Variation in Properties of Oxides Within a Period

One way to compare the properties of the main group elements across a period is to examine the properties of a series of similar compounds. Because oxygen combines with almost aU elements, we will compare the properties of oxides of the third-period elements to see how metals differ from metalloids and nonmetals. Some elements in the third period (P. S. and Cl) form several types of oxides, but for simplicity we will consider only those oxides in which the elements have the highest oxidation number. Table 7.4 lists a few general characteristics of the.se oxides and some specific physical properties of the oxides of third-period elements. 

TABLE 7.4 I Some Properties ot Oxiiks of the Third-Peruxi Elements 

Melting point (°C) Boiling point t°C) Acid-base nature 

Certain oxides such as CO and NO are neutral that is, they do not react with water to produce acidic or basic solutions. In general, oxides of nonmetals are either addic or neutral. 

Most oxides can be classified as acidic or basic depending on whether they produce acids or bases when dissolved in water (or whether they react as acids or bases). Some oxides amphoteric, which means that they display both acidic and basic properties. The first two oxides of the third period, Na20 and MgO, are basic oxides. For example, Na20 reacts with water to form the base sodium hydroxide  

---