|The Activity of Metals||Classifying Metals Based on Activity|
|Predicting the Product of Main Group Metal Reactions|
The Activity ofMetals
The primary difference between metals is the ease with whichthey undergo mmsanotherstage2019.comical reactions. The elements toward the bottomleft corner of the periodic table are the metals that are themost active in the sense of being the most reactive.Lithium, sodium, and potassium all react with water, for example.The rate of this reaction increases as we go down this column,however, because these elements become more active as they becomemore metallic.
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Classifying MetalsBased on Activity
The metals are often divided into four classes on the basis oftheir activity, as shown in the table below.
Common Metals Divided into Classes on theBasis of Their Activity
|Class I Metals: The Active Metals|
|Li, Na, K, Rb, Cs (Group IA)|
|Ca, Sr, Ba (Group IIA)|
|Class II Metals: The Less Active Metals|
|Mg, Al, Zn, Mn|
|Class III Metals: The Structural Metals|
|Cr, Fe, Sn, Pb, Cu|
|Class IV Metals: The Coinage Metals|
|Ag, Au, Pt, Hg|
The most active metals are so reactive that they readilycombine with the O2 and H2O vapor in theatmosphere and are therefore stored under an inert liquid, suchas mineral oil. These metals are found exclusively in Groups IAand IIA of the periodic table.
Metals in the second class are slightly less active. Theydon"t react with water at room temperature, but they reactrapidly with acids.
The third class contains metals such as chromium, iron, tin,and lead, which react only with strong acids. It also containseven less active metals such as copper, which only dissolves whentreated with acids that can oxidize the metal.
Metals in the fourth class are so unreactive they areessentially inert at room temperature. These metals are ideal formaking jewelry or coins because they do not react with the vastmajority of the substances with which they come into dailycontact. As a result, they are often called the "coinagemetals."
Predicting the Productof Main Group Metal Reactions
The product of many reactions between main group metals andother elements can be predicted from the electron configurationsof the elements.
Example: Consider the reaction between sodium and chlorine toform sodium chloride. It takes more energy to remove an electronfrom a sodium atom to form an Na+ ion than we get backwhen this electron is added to a chlorine atom to form a Cl-ion. Once these ions are formed, however, the force of attractionbetween these ions liberates enough energy to make the followingreaction exothermic.
|Na(s) + 1/2 Cl2(g) " width="17" height="9" sgi_fullpath="/disk2/mmsanotherstage2019.comistry/genmmsanotherstage2019.com/public_html/topicreview/bp/ch9/graphics/rarrow.gif"> NaCl(s)|| |
Ho = -411.3 kJ/mol
The net effect of this reaction is to transfer one electronfrom a neutral sodium atom to a neutral chlorine atom to form Na+and Cl- ions that have filled-shell configurations.
Potassium and hydrogen have the following electronconfigurations.
|K: ||H: 1s1|
When these elements react, an electron has to be transferredfrom one element to the other. We can decide which element shouldlose an electron by comparing the first ionization energy forpotassium (418.8 kJ/mol) with that for hydrogen (1312.0 kJ/mol).
Potassium is much more likely to lose anelectron in this reaction, which means that hydrogen gains anelectron to form K+ and H- ions.
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|Practice Problem 1:|
Write a balanced equation for the following reaction.
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