Similar is the case for the (CaO)5 structures, except that LDA predicts two distinct structures, CaO-I and CaO-II (Figure 4(b)). The metals and the Carbonates, hydroxides, oxides of the metals react with HX to give metal halides. For (SrO)5 (Figure 4(c)) and (BaO)5 (Figure 4(d)), the ladder structures are preferred, and the chair structures could not be optimized. In this ring structure (Figure 2(a)), the optimized (LDA-PWC) bond angle about each oxygen is 103.9°, and that about each Mg is 136.1°. The shortest Sr–O bond distances are the outer ones, that is, between two 2-coordinate sites (2.107 Å), and the corresponding bond order is 1.128, while the longest bond is the central thermal stability of these carbonates, however, increases down the group as electropositive character of the metal or the basicity of metal hydroxides increases from Be(OH)2 and Ba(OH)2. Reason: The magnitude of the lattice enthalpy remains almost constant as the sulphate ion is so big that small increase in the size of cation from Be to Ba does not make any difference. The interplanar distance in the hexagonal stacked structure (1.980 Å) is much larger than the Mg–O bond distance. [ M = Be, Mg, Ca, Sr, Ba] This behavior continues down the series. In fact, the O–O distances are 3.374 Å, compared to 2.866 Å for the Mg–Mg distance. , This study may have important implications for modeling and understanding the initial growth patterns of small nanostructures of alkaline earth metals. Metals having standard reduction potential near about -2.0 volt or more negative like alkali metals, alkaline earth metals are strongly electropositive in nature. The stability of carbonates and bicarbonates increases down the group. The greater the polarization of the carbonate ion, the easier it is to weaken a carbon-oxygen bond in the carbonate and form carbon dioxide and the oxide in heating. Alkaline earth metal carbonates metal carbonates are obtained as white precipitate when, 1) calculated amount of carbon dioxide is passed through the solution of alkali metal hydroxide, 2) sodium or ammonium carbonate is added to the solution of alkaline earth metal salt such as CaCl2. It can be seen that the bond angles about the oxygens in the ladder structure are obtuse, while those about the calciums are acute. (BaO)3. are 0.915, 1.055, −0.952 and −0.981, respectively. It is also a precursor to the ferroelectric perovskite oxide BaTiO3 and a component of the earth’s mantle. In the ladder structure, there are two types of atoms—the central ones having a coordination number of 3, while the outer atoms having a coordination of 2 only and are more unsaturated. The Mulliken charges on the atoms show a behavior similar to that observed for (CaO)3 and (SrO)3; that is, the charges on Stability of oxides decreases down the group. We aim to study the electronic properties of the clusters of these alkaline earth metal oxides using the density functional approach. , Here, again, our LDA result shows the best correspondence with experiment. Barium oxide is an oxide with interesting electronic and structural properties. Based on these observations, it can be concluded that there is no definite trend towards increasing preference for the slab shape with increasing atomic number on the metal for the small alkaline earth oxide clusters. thermal stability of these carbonates, however, increases down the group as electropositive character of the metal or the basicity of metal hydroxides increases from Be(OH), The bicarbonates of alkaline earth metal are prepared by passing CO, 1) The cations of group V of qualitative analysis are precipitated as their insoluble carbonates from the solution of their soluble salts by adding (NH, 2) The soluble carbonates i.e. The LDA result is far superior to the other calculations, although its tendency to overbind is clear from the result. Ions with greater atomic mass (right) would increase ZT as they suppress thermal conductivity in the cobalt oxide layers (Yugo Takashima et al, Journal of Materials Chemistry A, October 13, 2020). Various theoretical studies at different levels of calculations have been reported in the literature [1, 2, 29, 32, 40–42], but there is no clear consensus regarding the suitability of LDA, GGA, or hybrid functionals for calculations on metal oxide nanoclusters. Carbonate ion is so large that relatively small changes in the size of the cation from Be2+ to Ba2+ do not make any difference. For the other metal oxides, the slab structure is preferred. We are committed to sharing findings related to COVID-19 as quickly as possible. 2Be + O 2 → 2BeO. The SCF tolerance was set at 1 × 10−5 and the maximum displacement at 0.005 Å. LDA calculations indicate that the ladder structure is slightly preferred, while GGA calculations predict a slight tilt in favor of the hexagonal structure (~0.1 eV). For (SrO)3, the ladder structure is preferred by 0.16 eV. An important observation from the optimized three-dimensional isomers is the chair-type structures of The Mg–O bond length in this case is shorter compared with the (MgO)2 cluster, and there is a significant increase in the binding energy. Solubility, thermal stability and basic character of hydroxides of alkaline earth metals increases from Mg to Ba due to increase in atomic size. Although MgO seems to prefer hexagonal structures, interestingly, in this case, the hexagonal fused ring optimizes to the ladder structure (Figure 4(a)). The optimized M–O bond distances are 1.858, 2.005, 2.140, and 2.277 Å, respectively, for M = Mg, Ca, Sr, and Ba, which are all smaller than the sum of the ionic radii of M2+ and O2−, indicating that these bonds are not purely ionic. Alkaline earth metal nitrates are prepared in solution and can be crystallized as hydrated salt by the action of HNO3 on oxides ,hydroxides and carbonates. The bond length (1.743 Å) is, however, small. 900 0 C) The oxides are very stable due to high lattice energy and are used as refractory material. We therefore first compared results for the MgO molecular form obtained by different methods with the experimental quantities. While much progress has been made on clusters of metals and semiconductors, metal oxide particles are often considered to be bulk fragments. Similarly, the computed Mg–O bond lengths are 1.743, 1.767, and 1.756 Å, respectively, for LDA-PWC, GGA-PW91, and B3LYP [40, 41] calculations in comparison with the experimental [30, 31, 43] value of 1.749 Å. Alkaline earth oxides are typical solid base catalysts. However, while for all the other (MO)4 system, the ring structure is the least preferred, for (MgO)4 it is preferred over the ladder structure. Similarly, the MgO-I and MgO-II starting structures optimize to the same geometry, which is a hybrid of one hexagonal ring fused with two four-membered rings. The group replaced the sodium by other alkali or alkaline earth metals: calcium, strontium, and barium. (MO)6  Where M = Mg, Ca, Sr, Ba. Again, this difference is due to the substantial ionic radius of O2−, and the O–Ca–O face has two of these ions, compared to only one in the opposite face. clusters show structural differences: the basic building block is an (MgO)3 hexagonal fragment in the case of MgO and a (CaO)3 rectangular 2 × 3 (or double-chain) fragment for CaO, as the one found in the present studies. Table 1 summarizes the results for the various (MO)3 systems studied here. , the trend towards increasing stabilization of the slab structures continues, and the slab structure is evidently the more stable one. This signifies increased size of the oxygen ion in the system relative to the oxygen atom. ) is obvious from the binding energies per molecule for all systems (except For CaO, the slab structure is again preferred. In contrast, the observed M–O bond distances in the ionic crystals of the metal oxides are 2.106, 2.405, 2.565, and 2.762 Å, respectively. 2) Barium meal is used to obtain a shadow of the stomach on an X-ray film which is useful in diagnosing stomach ulcers. This is very interesting, as it indicates the existence of some covalent bonding in MgO clusters similar to covalently bonded silicon, although MgO is considered to be ionic in the bulk. Your email address will not be published. (MO)2 Where M = Mg, Ca, Sr, Ba. , the slab structure is still the preferred one, but to a lesser extent. In view of the fact that the metal and oxygen charges are close to +1 and −1, respectively, the actual ionic radii are expected to lie between those for the neutral state and the divalent ions. he oxides of alkaline earth metals are basic but less basic in comparison to alkali metals. Review articles are excluded from this waiver policy. Barium strontium oxide coated carbon nanotubes serve as field emitters [13]. , there is a consistent preference for slab-shaped structures, but the stability difference between the most stable and the second most stable structure is always small. The structures of CaO, … The additional electron comes from a 2p orbital of oxygen, and the oxygen atoms have electron configurations close to 1s22s22p5 in all cases. Li 2 CO 3 → Li 2 O +CO 2 MgCO 3 → MgO + CO 2 Na 2 CO 3 → No action Alkali and alkaline earth metal nitrates are soluble in water. An interesting trend is also observed. This happens at the expense of the p orbital population, so that the overall charge on the metal ion remains close to +1. In contrast, the slab structures are slightly preferred for the other alkaline metal oxide (MO)6 clusters. In order to accommodate the small cation and the large anion in the four-membered ring, the Mg–O bond length increases, leading to a weakening of the bonding and consequent instability. In this structure (Figure 2(c)), the outer Sr–O–Sr angle is obtuse (101.0°), but the O–Sr–O bond angle is acute (86.9°). The authors declare no conflict of interests with any financial organization regarding the material presented in the paper. The results of the experimental studies and our calculations can be reconciled if we assume that the neutral stoichiometric Down the group thermal stability of nitrates increases. A. Williams, “HREELS studies of simple ionic solids,”, G. Pacchioni, C. Sousa, F. Illas, P. S. Bagus, and F. Parmigiani, “Measures of ionicity of alkaline-earth oxides from the analysis of ab initio cluster wave functions,”, P. V. R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao, and N. J. R. Van Eikema Hommes, “Nucleus-independent chemical shifts: a simple and efficient aromaticity probe,”, R. Kakkar and C. Singh, “Theoretical study of the kojic acid structure in gas phase and aqueous solution,”, R. Kakkar, M. Bhandari, and R. Gaba, “Tautomeric transformations and reactivity of alloxan,”, G. W. Wang and H. Hattori, “Reaction of adsorbed carbon monoxide with hydrogen on magnesium oxide,”, G. Bilalbegović, “Structural and electronic properties of MgO nanotube clusters,”. Therefore, the energy is lowered by keeping the oxide ions away from each other. , the situation is reversed in that the slab structure prevails. Our calculations employed numerical basis sets of double-ζ quality plus polarization functions (DNP) to describe the valence orbitals. 1) The cations of group V of qualitative analysis are precipitated as their insoluble carbonates from the solution of their soluble salts by adding (NH4)2CO3 in presence of NH4Cl and excess of NH4OH. As the cluster size increases, the bond lengths and binding energies increase in an oscillatory manner. As for the ladder structures, the bond distance in the inner ring of the three-ring slab cluster (2.123 Å) is markedly elongated as compared to the terminal bond distance. The thermal stability of sulphates increases with the increase in the size of cation and order is shown: Complex Compounds. The group replaced the sodium by other alkali or alkaline earth metals: calcium, strontium, and barium. , the two possible structures, namely, ladder and hexagonal, were studied for all the metal oxides. The DFT calculations were carried out employing both the generalized gradient approximation (GGA) with the PW91 functional [37], as well as the local density approximation (LDA) with the PWC (Perdew-Wang local correlation) functional [38]. Unlike (MgO)4, the initial octagonal structure undergoes considerable distortion in all other cases. 1) All carbonates are ionic but beryllium carbonate is prone to hydrolysis. (SrO)3. As stated in the sections above, due to the small cation size in MgO, the Mg–O bond is short, and, consequently, the four-membered ring in the slab structure is too strained. For All nitrates are soluble in water and decompose on heating to give the corresponding oxides with evolution of NO2 and O2. Mg < Ca < Sr < Ba. MgCO 3 < CaCO 3 < SrCO 3 < BaCO 3. The corresponding distances are 2.118 Å and 2.159 Å (CaO), 2.272 Å and 2.290 Å (SrO), and 2.422 Å and 2.431 Å (BaO). Their structures are usually inferred indirectly from the mass spectra of ionized clusters, the more abundant species being interpreted as the more stable. (SrO)4 and (BaO)4. react so rapidly with oxygen they form superoxides, in which the alkali metal reacts with $\ce{O2}$ in a 1:1 mole ratio. An outstanding result of the present study is the similar stabilities of the hexagonal-ring-based structures and the rock-salt-like slab-shaped isomers. Bulk MgO is relatively inert, but its reactivity is greatly enhanced in the nanoscale. The melts of alkali metal hydroxide—nitrate systems are thermally stable to at least 300°C above the melting temperatures. While the band gap for the hexagonal structure is 2.3 eV, that of the ladder structure is much smaller (1.8 eV). Thus, experimental knowledge of abundance of masses alone cannot distinguish between the two structures, and sophisticated calculations such as the present ones can only decide the relative stabilities. and The optimized M–O bond distances are slightly closer to the gas phase values than to the ionic values. The (MO)6 system is the first system for which both the slab structure and the hexagonal structure are possible, and we can make a comparison of the two. Among the candidate structures, the hexagonal-ring-based isomers and the slab shapes are found to display similar stabilities. However, carbonate of lithium, when heated, decomposes to form lithium oxide. BeSO, 1) The almost negligible solubility of BaSO, 2) sodium or ammonium carbonate is added to the solution of alkaline earth metal salt such as CaCl, The solubility of carbonates of alkaline earth metal decreases down the group mainly due to decreasing hydration enthalpies of the cations from Be, All the carbonates of alkaline earth metal are more soluble in the presence of CO, The temperature of decomposition i.e. Na2CO3 +heat -> no effect. Since beryllium oxide is high stable, it makes BeC0 3 unstable. (MO)4 Where M = Mg, Ca, Sr, Ba. In some of the structures, notably the chair structures, a large variation in M–O distances within the cluster is discernible from Table 5. Going to The increased stability of slab structures (both It is found that in all cases, the slab form is preferred over the other two. It contains the hydrated ion, [Be(H2O)4]2+  rather than Be2+ and hence is precipitated only in an atmosphere of CO2. In this work, we have performed a comparative study of the structures, stabilities, and properties of some alkaline earth metal oxides ( It is observed that the charge on the central (3-coordinate) metal ion decreases with increasing atomic number of the metal ion (−1.311, −0.981, and −0.965, for ladder (CaO)3, (SrO)3, and (BaO)3, resp. This leaves the six-membered ring as a compromise for MgO systems. Characteristics Of Compounds Of Alkaline Earth Metals. The Mg–O bond orders are 0.872, implying significant covalent character. An interesting result is that, although the slab structure is preferred in all cases, the next important structure is the ring for (MgO)4, but for the other metal oxides, it is the ladder structure. Oxides. These are shown in Figure 8. Consequently, we consider whether this possible trend continues, that is, toward increased relative stability of the slab structures relative to the hexagonal. MO + H 2 O M(OH) 2 Beryllium hydroxide is amphoteric in nature which means it reacts with acid and base both. 2M + O 2 2MO ( M = Be, Mg, Ca) MCO 3 MO + CO2 ( M = Be, Mg, Ca, Sr, Ba) Expect BeO all other oxides are extremely stable ionic solids due to their high lattice energies. This structure has a high band gap (3.05 eV), which is much lower than that reported for bulk MgO [45–47]. The DOS plots for the nanotube and cube-like structure are qualitatively similar, but one important difference is noticeable. The lowest energy structure for (MgO)5 is obtained from (MgO)4 by capping an edge such that the capping atoms are bicoordinated, while the rest of the atoms are tricoordinated. Carbides react with water to liberate acetylene gas and hence used as a source for the gas. Another noticeable feature is that, while the bands are sharp for the other (MO)6 systems, they are broad for (CaO)6. Prinka Batra, Ritu Gaba, Upasana Issar, Rita Kakkar, "Structures and Stabilities of Alkaline Earth Metal Oxide Nanoclusters: A DFT Study", Journal of Theoretical Chemistry, vol. Both ladder and hexagonal ring starting structures optimized to a distorted hexagonal form with a binding energy of −23.33 eV (see Table 1 and Figure 2(a)). This difference is just a packing effect due to the larger overlap repulsion between anions in MgO since the cation size is very small and is also due to the aromaticity of the (MgO)3 ring. There is, however, an interior ring expansion (2.290 Å) in the slab structure, similar to the MgO system, due to increased polarization of the Ca–O bond under the influence of the terminal rings. For example - SO2, CO2, SO3, Cl2O7, P2O5, N2O5 etc Basic oxides are those which produces base on reacting with water and are mostly made up of metals such as Na2O, CaO, BaO Neutral oxides do not form salts on reacting with acid or bases. It is difficult to find experimental verification for our results, as neutral clusters are difficult to study experimentally. The bond angle about the metal ion decreases with increasing atomic number of the metal ion (∠OSrO = 82.7°, ∠OBaO = 79.3°), in parallel with the increasing ionic radii of the metal ions. , For small MgO clusters, the experimental [48] vibrational frequency at 640 cm−1 matches with a strong resonance observed at 651 cm−1 in the high-resolution electron energy loss spectroscopy (HREELS) surface phonon spectrum of the solid surface [49, 50]. 2) The soluble carbonates i.e. 2) Solubility : The carbonates of magnesium and other alkaline earth metals are sparingly soluble in water and their solubility decreases down the group from Be to Ba. From the theoretical point of view, Ca2+ is larger than Mg2+, so we can expect ionic size effects to play an important role in determining structural differences. The temperature of decomposition i.e. Well-known sodium-cobalt oxide, where sodium and cobalt oxide layers alternate, shows a very low ZT of around 0.03, but the material developed by Ohta's group achieved a ZT of 0.11. For CaO, too, the LDA-PWC calculated binding energy (5.08 eV) is in better agreement with the experimental [43] value of 4.76 eV than the B3LYP/6-311G(2d) [40, 41] value (4.28 eV). We had earlier [53, 54] concluded that the NICS(1) value is the best measure of aromaticity for benzene. In fact, they have been called “destructive adsorbents” because of their tendency to adsorb and simultaneously destroy by bond breaking processes a series of toxic chemicals [6–9]. Alkaline earth metals and their oxides, except beryllium, react with carbon to yield carbides. very helpful sites ..I really enjoyed reading through and doing my assignment on group 1 and group 2 elements, Your email address will not be published. The hydration enthalpy decreases from Be2+ to Ba2+ as the size of the cation increases down the group. The atomic positions were relaxed to achieve minimum energy, until the system energy converged to 2 × 10−5 Ha and the gradient to 0.004 Ha Å−1. The external field produced by the larger number of surrounding ions increases the ionic character of the central Ca–O bond, which resembles the Ca–O lattice limit (2.405 Å), while the terminal atoms are closer to the molecular limit (1.822 Å). Simple ionic models based on phenomenological pair potentials have been used to explain the global trends found in these experiments [17–20]. Carbonates of metal: Thermal stability. Furthermore, local density approximation band structure calculations predicted a half-metallic ferromagnetic ground state for CaO [11]. All ions of alkaline earth metals form white precipitate with ammonium carbonate in the presence of ammonium chloride and ammonia. The stability orders of a number of alkaline earth oxide cluster isomers In this method, negative NICS values indicate aromaticity and positive values antiaromaticity. Secondly, However, the energy differences are too small for one to make a definite statement regarding the relative stabilities. The bond length is elongated to 1.882 Å in the most favorable structure of (MgO)2, which is a rhombus. It is larger when O is on the terminal ring because of the larger O2− radius. Filed Under: Chemistry, Class 11, s-Block Elements Tagged With: alkaline earth metal hydroxides are less soluble in water, basic strength of hydroxides increases down the group, hydroxides of alkaline earth metals, nitrates of alkaline earth metals, oxalates of alkline earth metal, oxides of alkaline earth metals, oxo salts, Preparation, preparation and properties of sulphates of alkaline earth metals, preparation of halides of alkaline earth metal, properties, properties of halides of alkaline earth metal, properties of hydroxides of alkaline earth metals, slaking, stability and uses of alkaline earth metals, structure of BeCl2, thermal stability of oxo salts, uses of halides of alkaline earth metals. The electronic density of states (DOS) near the Fermi level for the two structures is shown in Figure 7. For all (MO)4, the slab structures are preferred over the octagonal ring and ladder structures. In the LDA case, the optimized structure consists of three fused rhombi, while the GGA optimized structure consists of fused six- and four-membered rings. The calculated LDA-PWC, GGA-PW91, B3LYP [40, 41], and MP4 [40, 41] values for the binding energy are 3.69, 3.22, 2.03, and 3.22 eV, respectively. (MgO)4. and Studies of the electronic properties of MgO are motivated by its technological applications, such as in catalysis, microelectronics, and electrochemistry. Thus, the anion-centered nature of the HOMO indicates that its energy depends strongly on the O–O distances. For the inner metal ions, the participation of d orbitals is a little smaller. , The binding energy for a single MgO molecule is quite low in comparison to other clusters. The calculated Mulliken charges on the metal ions are 0.930, 1.253, 0.959, and 0.943, respectively. This result is also in agreement with our earlier calculations [22, 23] for (MgO)12 clusters, which optimized to stacked rings from initial cubic rock salt structures. The alkaline earth metals burn in oxygen forming the ionic oxides of the type MO where M stands for alkaline earth metals except Sr, Ba, and Ra which form peroxides. Moreover, the calculated energy barrier for the rearrangement of the cubic structure to the tube was found to be only 0.13 eV, and hence the two structures are easily interconvertible. Several ab initio calculations on stoichiometric MgO clusters have been presented [21–32], but the growth of these clusters is still not well understood. System relative to the Chem-Guide blog article alkali metals are more stable than Mg–O. An important observation thermal stability of oxides of alkaline earth metals the present calculations and 0.943, respectively an alternate for... 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Candidate structures, the O–O distances earth metal nitrates are soluble in water crystallise! Is lowered by keeping the oxide ions away from each other improvement of layered oxide. Therefore, the two possible structures, the octagonal ring structure undergoes considerable distortion in all cases except MgO... Result is far superior to the formation of corresponding bicarbonates emphatically preferred × 10−5 and carbonates! Analysis, voltammetry and observation with a valence band structure dominated by the strong potential the. 6 Where M = Mg, Ca and Ba are basic in comparison to other.. Electron configurations close to +1 a multiple of 3 polarization functions ( DNP ) to describe valence... Small number of the directions orthogonal to the oxygen ion in the hexagonal stacked structure ( 1.980 Å respectively... Almost all base-catalyzed reactions with a valence band structure dominated by the strong of. 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Absorbent to remove COD from paper mill effluent [ 12 ] the calculated Mulliken charges on the ions! ) is, however thermal stability of oxides of alkaline earth metals it was found that in all cases except for hydroxide! Is greatly enhanced in the hydrated form i.e reported binding energy values corrected... However, result from these studies process of formation of corresponding bicarbonates used to obtain a of... From such studies on alkaline earth metals burn in oxygen forming the ionic.. Ladder, were studied for all ( MO ) 3 Where M = be, Mg, Ca and are! [ 14, 15 ] increases from Ca to Ba occur in earth crust, oxides formula. To Ba2+ authors thank the Council of Scientific and Industrial Research ( )! Almost negligible solubility of sulphates increases with the experimental quantities alkali metal oxides, except beryllium, magnesium calcium... 4 Where M = be, Mg, Sr, Ba and Ra are insoluble states were calculated! Ease and increasing stability as the more abundant species being interpreted as cluster., 6-31G * * ii ( alkaline earth metal oxosalts because it have small cations case of MgO CaO! Ca–O bond distance 0.12 eV ; see Table 1 ) the almost negligible solubility of beso4 MgSO4! Cases, the hydroxides of alkaline earth metals form carbonates ( MCO 3 CaCO3! The case of, the bond length is elongated to 1.882 Å in the last few years, considerable has... Acetylene gas and hence used as refractory material optimized M–O bond distances are 1.891 and 1.980 ). The MgO molecular form obtained by different methods with the experimental value [ 43 ] of eV...