The Group 2A Elements

The Group 2A elements (with the valence electron configuration ns2) are very reactive, losing their two valence electrons to form ionic compounds that contain M2+ cations. These elements are commonly called the alkaline earth metals because of the basicity of their oxides  

Only the amphoteric beryllium oxide (BeO) also shows some acidic properties, such as dissolving in aqueous solutions containing hydroxide ions  

The more active alkaline earth metals react with water as the alkali metals do, producing hydrogen gas  

Calcium, strontium, and barium react vigorously at 25°C. The less easily oxidized beryllium and magnesium show no observable reaction with water at 25°C, although magnesium reacts with boiling water. Table 18.7 summarizes various properties, sources, and preparations of the alkaline earth metals. 

The heavier alkaline earth metals react with nitrogen or hydrogen at high temperatures to produce ionic nitride or hydride salts. For example  

Calcium metal reacting with water to form bubbles of hydrogen gas. 

See Section 9.8 for a discussion of the feasibility of using hydrogen gas as a fuel. 

Although hydrogen can react with transition metals to form compounds such as UH3 and FeHg, most of the interstitial hydrides have variable compositions (often called nonstoichiometric compositions) with formulas such as LaH2.76 and VHo.sg. The compositions of the nonstoichiometric hydrides vary with the length of exposure of the metal to hydrogen gas. 

An amphoteric oxide displays both acidic and basic properties. 

Boiling points of covalent hydrides were discussed In Section 10.1. 

Unless otherwise noted, all art on this page is Cengage Learning 2014. 

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The same effects felt by the group 1A elements when a single electron is lost are felt by the group 2A elements when two electrons are lost. For example, loss of two valence-shell electrons from an Mg atom (Is2 2s2 2p6 3s2) gives the Mg2+ cation (Is2 2s2 2p6). The smaller valence shell of the Mg2+ cation and the increase in effective nuclear charge combine to cause a dramatic shrinkage. In the same way, a similar shrinkage is encountered whenever any of the metal atoms on the left-hand two-thirds of the periodic table is converted into a cation. 

The unusually large Ej values for the group 2A elements Be, Mg, and so forth can be explained by their electron configurations. Compare beryllium with boron, for example. A 2s electron is removed on ionization of beryllium, but a 2p electron is removed on ionization of boron ... 

Radium Radium, the heaviest of the group 2A elements, occurs with uranium and was isolated as its chloride salt from the mineral pitchblende by Marie and Pierre Curie in 1898. Radium is highly radioactive, and no more than a few kilograms of the pure metal have ever been produced. Though used for many years as a radiation source for cancer radiotherapy, better sources are now available, and there are no longer any commercial uses for radium. 

Alkaline earth metal(s) The group 2A elements of the periodic table. 

Note that the use of a Roman numeral in a systematic name is required only in cases in which more than one ionic compound forms between a given pair of elements. This case most commonly occurs for compounds containing transition metals, which often form more than one cation. Elements that form only one cation do not need to be identified by a Roman numeral. Common metals that do not require Roman numerals are the Group 1A elements, which form only 1+ ions the Group 2A elements, which form only 2+ ions and aluminum, which forms only Al3+. Common transition metals that do not require a Roman numeral (because they form only one ion) are zinc (Zn2+) and silver (Ag+). 

The most commonly used strong base in the laboratory is sodium hydroxide. It is cheap and soluble. (In fact, all of the alkali metal hydroxides are soluble.) The most commonly used weak base is aqueous ammonia solution, which is sometimes erroneously called ammonium hydroxide there is no evidence that the species NH4OH actually exists. All of the Group 2A elements form hydroxides of the type M(OH)2, where M denotes an alkaline earth metal. Of these hydroxides, only Ba(OH)2 is soluble. Magnesium and calcium hydroxides are used in medicine and industry. Hydroxides of other metals, such as Al(OH)3 and Zn(OH)2 are insoluble and are less commonly used. 

The group 2A elements (the alkaline earth metals) have higher first ionization energies than the alkali metals do. The alkaline earth metals have two valence electrons (the outermost electron confignration is ns ). Because these two s electrons do not shield each other well, the effective nuclear charge for an alkaline earth metal atom is larger than that for the preceding alkali metal. Most alkaline earth compounds contain dipositive ions (Mg +, Ca, Sr, Ba +). The Be ion is isoelectronic with Li and with He, Mg is isoelectronic with Na and with Ne, and so on. 

FIGURE 8.15 The Group 2A elements the alkaline earth metals. 

The Group 2A Elements The Group 3A Elements The Group 4A Elements The Group 5A Elements The Chemistry of Nitrogen... 

Table 20.6 Selected Physical Properties, Sources, and Methods of Preparation of the Group 2A Elements ...

Group 4. Insoluble phosphates At this point the solution contains only metal ions from groups lA and 2A of the periodic table. Adding (NH4)2HP04 to a basic solution precipitates the group 2A elements Mg, Ca, Sr ", and Ba " because these metals form insoluble phosphates. 

The Group 2A elements (Be, Mg, Ga, Sr, Ba, and Ra) are called the alkaline earth metals. Compared with the alkali metals, the alkaline earth metals are harder, are more dense, and melt at higher temperatures. These elements form cations with a + 2 chaise. Because the valence electrons of alkaline earths are held more tightly, they are less reactive than their alkali metal neighbors. All the alkaline earth metals react with oxygen to form an oxide MO, where M is the alkaline earth. 

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