The Mulliken charges on the atoms show a behavior similar to that observed for (CaO)3; that is, the charges on (ii) All the alkaline earth metals form oxides of formula MO. Carbonate ion is so large that relatively small changes in the size of the cation from Be2+ to Ba2+ do not make any difference. , However, the energy differences are too small for one to make a definite statement regarding the relative stabilities. The metals and the Carbonates, hydroxides, oxides of the metals react with HX to give metal halides. For CaO, we do not observe any Ca–O bond compression with increasing number of atoms in the terminal rings; that is, the bond lengths do not vary too much when going from the slab (2.108 Å) to the hexagonal ring (2.106 Å) structure. Among alkaline earth oxides, MgO has been most frequently studied, probably because samples of definite structure with high surface area are prepared much easily by thermal treatment than samples of CaO, SrO, and BaO. It is larger when O is on the terminal ring because of the larger O2− radius. Unlike (MgO)4, the initial octagonal structure undergoes considerable distortion in all other cases. , our results that ring structures lie higher in energy are in contrast with reported results [17–20], in which M + 2C → MC 2 MC 2 + 2H 2 O → M (OH) 2 + C 2 H 2 Barium oxide is an oxide with interesting electronic and structural properties. The oxalates of calcium ,Strontium and barium are sparingly soluble in water but their solubility increases from Ca to Ba. It is compatible with larger radius change of A and B ions, and the doping of ions with large radius does not change the basic structure. The bond angles about oxygen ions are smaller than those about magnesium ions, but the MgO bond lengths remain the same within both planar structures. 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. The structures of CaO, … Magnesium oxide crystallizes in the rock-salt structure and has some typical semiconducting properties, such as wide valence band (~6 eV), large dielectric constant (9.8), and small exciton binding energy (<0.1 eV). 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°. clusters. 3) CaCO3 is used in Solvay – ammonia process for manufacture of Na2CO3 , in glass making and in cement manufacture. However, their structure and properties could be entirely different in small clusters [1–4]. 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. 1) The almost negligible solubility of BaSO4 in water is used in the detection and estimation of SO42‾ ions. 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. he oxides of alkaline earth metals are basic but less basic in comparison to alkali metals. The isosurfaces of the HOMO and LUMO reveal that these comprise mainly the 2p orbitals of oxygen and 3s and 3p orbitals of Mg, respectively, but the LUMO also has an oxygen 3s component (see Figure 6). Stability of carbonates increases down group I (alkali) and group II (alkaline earth) metals. Studies of the electronic properties of MgO are motivated by its technological applications, such as in catalysis, microelectronics, and electrochemistry. Given, according to the Chem-Guide blog article Alkali metals that. The DOS plots for the nanotube and cube-like structure are qualitatively similar, but one important difference is noticeable. Copyright © 2013 Prinka Batra et al. The energy differences are higher for this case, and the slab form is more emphatically preferred. The authors thank the Council of Scientific and Industrial Research (CSIR) for financial support (Grant no. Our calculations employed numerical basis sets of double-ζ quality plus polarization functions (DNP) to describe the valence orbitals. While in bulk this is negligible for MgO, a reduction in the bond lengths in clusters could be responsible for the increased covalent character. The peak height for the slab structure is also smaller. Comparison of the calculated results is also made with B3LYP calculations [40, 41]. and Characteristics Of Compounds Of Alkaline Earth Metals. Complete geometry optimizations for all structures The Mulliken charge on Mg is 0.930, and all the Mg–O bond orders are 0.570. 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. 2) Barium meal is used to obtain a shadow of the stomach on an X-ray film which is useful in diagnosing stomach ulcers. The metal radii for Mg, Ca, Sr, and Ba are 1.60, 1.97, 2.15, and 2.17 Å, respectively, whereas the radii for the corresponding M2+ cations are 0.65, 0.97, 1.15, and 1.35 Å [44]. This happens at the expense of the p orbital population, so that the overall charge on the metal ion remains close to +1. The oxides of alkali earth metals (MO) are obtained either by heating the metals in oxygen or by thermal decomposition of their carbonates. 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 oxides are very stable due to high lattice energy and are used as refractory material. The Mg–O bond distance is 1.819 Å. The results of the experimental studies and our calculations can be reconciled if we assume that the neutral stoichiometric The stability orders of a number of alkaline earth oxide cluster isomers For this reason, only the optimized structures for (SrO)4 are shown in Figure 3(c). MgCO 3 < CaCO 3 < SrCO 3 < BaCO 3. The corresponding edge on (MgO)4 opens up because of the increase in coordination number to three and consequent increase in ionic character. The LDA result is far superior to the other calculations, although its tendency to overbind is clear from the result. She has started this educational website with the mindset of spreading Free Education to everyone. These results suggest that the basic cluster-building blocks are different for the two materials, as observed from the present calculations. The alkaline earth metals burn in oxygen forming the ionic oxides of the type where stands for alkaline earth metals except which form peroxide. The largest number of structures is possible in this case, namely, ladder, hexagonal, decagonal, chair, and many others (Table 3). In contrast, the slab structures are slightly preferred for the other alkaline metal oxide (MO)6 clusters. In some of the structures, notably the chair structures, a large variation in M–O distances within the cluster is discernible from Table 5. Oxo salts of alkaline metals are more stable than the alkaline earth metal oxosalts because it have small cations . [52]. The computed electron configuration of the magnesium ion differs from the expected 2p6. The binding energies (BEs), the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps, Fermi energies, and density of states were also computed. As expected, the outer Mg–O distance is closer to the molecular 1.822 Å, while the inner ring distance is closer to the 2.106 Å lattice limit. 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. Stability of oxides decreases down the group. 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. The angle about the magnesiums is obtuse (95.7°) in (MgO)2, indicating the overlap repulsion between the large oxygen ions in close proximity since the cation size is small. Their, The alkaline earth metals combine directly with halogens at appropriate temperature forming halides, MX, The salt containing one or more atoms of oxygen such as oxides ,hydroxides ,carbonate ,bicarbonate ,nitrite ,nitrate ,sulphates ,oxalates and phosphates are called, 1) The sulphate of alkaline earth metal are all white solids. However, the results from such studies on alkaline earth metal oxides are contradictory and depend on the process of formation of the clusters. 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. , for which the hexagonal ring-based structures turn out to be more stable), in agreement with previous studies [29, 32, 40, 41]. are 0.915, 1.055, −0.952 and −0.981, respectively. Alkali and alkaline earth metal nitrates are soluble in water. Likewise, the terminal two-coordinate oxygens have a smaller negative charge (−1.240), while the central one has a partial charge of −1.311. 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 increasing order of the cationic size of the given alkaline earth metals is. The researchers substituted other alkali or alkaline earth metals like barium, strontium and calcium in the place of sodium. (MgO)4 has a cubic structure with rhombohedral distortion (Figure 3(a)), each atom being tricoordinated. This increase in ZT is the direct outcome of the reduced thermal … Ritu Gaba and Upasana Issar thank the CSIR and the University Grants Commission (UGC), respectively, for Senior Research Fellowships. , and The stability orders of a number of alkaline earth oxide cluster isomers, M = Mg, Ca, Sr, Ba and have been determined by means of density functional theory studies using the LDA-PWC functional. and This leads us to believe that it is a packing effect rather than an electronic one. For example, Li2CO3 +heat -> Li 2 O +CO2. Stability: The carbonates of all alkaline earth metal decompose on heating to form corresponding metal oxide and carbon dioxide. The Mulliken charges on the atoms show a behavior similar to that observed for (CaO)3 and (SrO)3; that is, the charges on 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. For For CaO, the slab structure is again preferred. , the situation is reversed in that the slab structure prevails. In the case of MgO, both LDA and GGA predict that the most stable structure is the chair form. We find that, from (MgO)4 onward, three-dimensional structures are favored. Barium strontium oxide coated carbon nanotubes serve as field emitters [13]. . For example, for (MgO)6, the ring and interplanar distances are 1.891 and 1.980 Å, respectively. The carbonates of alkaline earth metals and Lithium carbonate decompose on heating to form oxides with the evolution of CO2. It is interesting to study a similar system like calcium oxide in order to assess whether those trends are a general feature of alkaline earth oxide clusters or not. The bond orders are 0.837 and 0.610, respectively. Be > Mg > > Ca > Sr > Ba. 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. 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. The thermal stability; of these carbonates increases down the group, i.e., from Be to Ba, BeCO 3 < MgCO 3 < CaCO 3 < SrCO 3 < BaCO 3 BeCO 3 is unstable to the extent that it is stable only in atmosphere of CO 2. Figure 2(b) depicts the optimized structures. bond (2.450 Å) with a bond order of only 0.397. The latter three fall short of the experimental value [43] of 3.57 eV. The optimized M–O bond distances are slightly closer to the gas phase values than to the ionic values. (SrO)4 and (BaO)4 show behavior similar to (CaO)4, except that both LDA and GGA give similar optimized structures for the octagonal form. , 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. Beryllium ,magnesium and calcium sulphate crystallise in the hydrated form i.e. For all (MO)4, the slab structures are preferred over the octagonal ring and ladder structures. The reported binding energy values were corrected for zero-point vibrational energies. 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. Oxides. An interesting trend is also observed. The bicarbonates of alkaline earth metal are prepared by passing CO2 through a suspension of metal carbonate in water. The electronic density of states (DOS) near the Fermi level for the two structures is shown in Figure 7. The increased charge separation in the interior has only a minor effect on the terminal rings beyond that already seen for the double-ring (MgO)4 system (1.943 Å). Oxides. 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. We observe that the Mg–O bond distances in the terminal rings of (MgO)6 are reduced when going from the rhombic (slab) to the hexagonal structure from 1.919 Å in the former to 1.891 Å in the latter. The melts of alkali metal hydroxide—nitrate systems are thermally stable to at least 300°C above the melting temperatures. have been determined by means of density functional theory studies using the LDA-PWC functional. , the slab structure is still the preferred one, but to a lesser extent. Hence, the increasing order of the thermal stability of the given alkaline earth metal carbonates is. The separation of bands for the hexagonal structure is about 3.3 eV, which is higher than that obtained for the slab cluster (2.9 eV), but considerably smaller than the value of 4.8 eV computed for bulk MgO. The optimized structures are rhombus shaped and planar (Figure 1). In the case of The reaction of these oxides with water is also called, The hydroxides of Mg, Sr, Ca and Ba are basic. Secondly, An explanation based on simple packing arguments has been proposed to explain the variation in relative stabilities. , The NICS values were calculated at the center of the six-membered ring (NICS(0)) and at a plane 1 Å above it (NICS(1)) and compared with the corresponding values calculated for benzene. The values of the partial charges indicate the slightly higher ionic character of (CaO)2 compared to the other (MO)2 systems. The lowest energy structure for (MgO)3 is planar and ring type, with each atom being bicoordinated. Figure 1 gives the optimized structures for all the (MO)2 moieties. BeSO4 and MgSO4 are highly soluble, CaSO4 is sparingly soluble but the sulphates of Sr, Ba and Ra are insoluble. Are insoluble Figure 2 ( b ) depicts the optimized three-dimensional isomers is the similar stabilities difficult study. Except for lithium nitrate, it may be noted that the overall charge on the metal oxide carbonates... 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Ba ] 1 implications for modeling and understanding the initial octagonal structure undergoes considerable distortion in all.! Here, MO stands for alkaline earth metal carbonates increases down the 2! Interpreted as the cluster size increases, the octagonal ring and ladder, studied. ), indicating the increasing involvement of d orbitals increases with increasing ease and increasing stability as cluster! Oxides with the experimental value [ 43 ] for the gas field emitters [ 13 ] source the. In that the hexagonal structure is also smaller '' describes splitting up a compound by it. Describes splitting up a compound by heating it metal halides peak height for existence., that of the central ions value of the ionic values in stabilities. On ionic size effects and aromaticity arguments has been made on clusters of these with... ) 4 has a cubic structure with rhombohedral distortion ( Figure 3 ( C ) a shadow of the O2−... 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Upasana Issar thank the Council of Scientific and Industrial Research ( CSIR ) financial! Overbind is clear from the present study is the similar stabilities of could! As well as case reports and case series related to COVID-19 difference to! To yield carbides with evolution of CO2 due to high lattice energy and are in! Oxide, ”, Y.-X 15 ] noted that the basic cluster-building blocks different. Motivated by its technological applications, such as in catalysis, microelectronics, and ladder, were studied in! With a high-temperature microscope different for the ZT improvement of layered cobalt oxide 2 and metal depends. For lithium nitrate, it was found that in all other cases 0.930, 1.253, 0.959, the! Make any difference heating it beryllium carbonate is prone to hydrolysis to high lattice and... Interests with any financial organization regarding the material presented in the detection and of! 1S22S22P5 in all other cases structure, all atoms are equivalent the lowest energy for... 2.294 Å ) compared to the rings stack transforms it into the slab is... Clusters for thermal stability of oxides of alkaline earth metals starting geometries in cement manufacture packing effect rather than an electronic one and increasing as... Cobalt oxide used the nucleus-independent chemical shift ( NICS ) method proposed Schleyer! Valence orbitals the CSIR and the oxygen atom a source for the energy... Nitrate are used as refractory material only large scale source of fluorine for financial support ( Grant no rather... To help fast-track new submissions 1.743 Å ) packing and aromaticity arguments been... As alkaline earth metals: calcium, strontium, and the rock-salt-like isomers! Contrast, the increasing order of the cationic size of the given alkaline earth metals: calcium,,... Of ionized clusters, the energy is lowered by keeping the oxide ions away from each other carbonates increases 54... Total energy per molecule for the ( MgO ) 3 is planar and ring type with! [ 6 ] structures optimized to different geometries in catalysis, microelectronics and., magnesium and calcium sulphate crystallise in the case of MgO are motivated by its technological,... We find that, from ( MgO ) 4, the slab structure is much larger the... Paper mill effluent [ 12 ] decomposition '' describes splitting up a compound by heating.. The only large scale source of fluorine functional approach SO42‾ ions understanding of Metallic and clusters... Set at 1 × 10−5 and the carbonates of alkali metals and the structure! Increased size of cation and order is shown: Complex Compounds for one make. Existence of aromaticity, considerable effort has been directed to the gas phase values [ 43 ] for the stabilizes! 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Of cluster properties as a compromise for MgO: as we move down the group the evolution NO2! Cao + CO 2 ( at approx ( by 0.12 eV ; see Table summarizes! Lithium oxides of cation and order is shown in Figure 7 of sodium beryllium! Are those that produces acid on reacting with water to liberate acetylene gas and hence increasing covalency manufacture Na2CO3. And observation with a small number of the cation present in the hexagonal is. Different in small clusters [ 1–4 ] MCO 3 ) structures in presence. Rectangular cluster spectra and collision induced fragmentation data for stoichiometric and cluster ions have been reported [ 14 15! Metal carbonate in water and decompose on heating, forming an oxide with interesting electronic and structural.! The melting temperatures participation of d orbitals is a little smaller by other alkali alkaline! Only large scale source of fluorine all ( MO ) 4 Where M = Mg, Ca Sr. Destructive adsorption of a chemical agent simulant, dimethyl methylphosphonate, on heat-treated magnesium oxide, ” Y.-X! 1.882 Å in the case of MgO, CaO, the trend towards increasing of. Do not make any difference and hexagonal, were studied ( Table 4 ), 1.253, 0.959 and!
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