Alkaline earth metals Group valence electrons

Alkaline Earth Metals Group 2 All group 2 metals have two valence electrons. When they form ions, they will have a charge of 2+. Group 2 alkaline earth metals are highly reactive and will react with water. 

The electron sea model for metals postulates a regular array of cations in a "sea" of valence electrons, (a) Representation of an alkali metal (Group 1A) with one valence electron, (b) Representation of an alkaline earth metal (Group 2A) with two valence electrons. 

In Table 6.2 we saw that the total number of orbitals in each shell equals r 1,4,9, or 16. Because we can place two electrons in each orbital, each shell accommodates up to 2rf electrons 2,8,18, or 32. We see that the overall structure of the periodic table reflects these electron numbers Each row of the table has 2, 8, 18, or 32 elements in it. As shown in T Figure 6.30, the periodic table can be further divided into four blocks based on the filling order of orbitals. On the left are two blue columns of elements. These elements, known as the alkali metals (group lA) and alkaline earth metals (group 2A), are those in which the valence s orbitals are being filled. These two columns make up the 5 block of the periodic table. 

Notice that for the alkali and alkaline earth metals and all the elements to the right of the 10th group the valence-electron numbers are 1, 2 and, respectively assumed to be given by the group number minus 10. For the transition elements, various assumptions have been used in some cases. 

Symbol Mg atomic number 12 atomic weight 24.305 a Group II A (Group 2) alkaline-earth metal atomic radius 1.60A ionic radius (Mg2+) 0.72A atomic volume 14.0 cm /mol electron configuration [Ne]3s2 valence +2 ionization potential 7.646 and 15.035eV for Mg+ and Mg2+, respectively three natural isotopes Mg-24(78.99%), Mg-25(10.00%), Mg-26(11.01%). 

The alkaline earth elements in group 2A—Be, Mg, Ca, Sr, Ba, and Ra—are similar to the alkali metals in many respects. They differ, however, in that they have ns2 valence-shell electron configurations and can therefore lose two electrons in redox reactions. Alkaline earth metals are thus powerful reducing agents and form ions with a +2 charge. 

The alkali and alkaline earth metals have their valence electrons in the s subshells. Groups 13 through 18 have their valence electrons located in the p subshells. The transition elements have their valence electrons in the d subshells, and finally, the lanthanides and actinides have their valence electrons in the f sublevel. 

Components of Zintl phases are metals A (Li-Cs, Mg-Ba) and semimetals X (B-Tl, Si-Pb, P-Bi, Te). The definition of the components of Zintl phases is not quite sharp, neither for the metals nor for the semimetals, until today. While the alkali- and alkaline earth metals are undoubtedly metals in the classical sense, there is still the vast field of transition metals T, which in Zintl type compoimds, might also occur. Electropositive T atoms may replace the main group metal A and electronegative ones tike a semimetal X. One of the wellknown examples here is CsAu (a diamagnetic semiconductor). This phase shows the typical properties of a valence compound according to the electron transfer description Cs Au [4]. 

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 ... 

This effect is also found for the bandwidth of the 0(2p) bands for the alkaline earth metal oxides which, at the LDA level of theory, decrease down the group from a calculated value of 4.44eV (MgO) to 1.83eV (BaO). This is partly due to the increase in lattice parameter, which spaces the O " ions more widely in BaO than in MgO. However, in addition, it is found that the outermost valence electrons for the metal ions interact more strongly with the 0(2p) states in BaO than in MgO, giving more localization of the electron density at O " and so a smaller anion in BaO [50]. 

Figure 4.The electron sea model, (a) represents an alkali metal with one valence electron and (b) represents an alkaline earth metal with two valence electrons. Illustration by Hans Cassidy Courtesy of Gale Group. 

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. 

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