Though the GGA-PW91 value (4.55 eV) is in slightly better agreement with experiment, the LDA Ca–O bond distance (1.818 Å) is in excellent agreement with the experimental [43] value (1.822 Å), while the GGA value is considerably larger (1.843 Å), reflecting the tendency of GGA to underbind. Oxides. The thermal stability of sulphates increases with the increase in the size of cation and order is shown: Complex Compounds. 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. 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). cluster ions have been reported [14, 15]. The mass spectra of 3) CaCO3 is used in Solvay – ammonia process for manufacture of Na2CO3 , in glass making and in cement manufacture. For Figure 5 depicts the optimized structures for the (MO)6 clusters for different starting geometries. An explanation based on simple packing arguments has been proposed to explain the variation in relative stabilities. The ladder structure is slightly preferred (by 0.12 eV; see Table 1). The alkaline earth metals burn in oxygen forming the ionic oxides of the type where stands for alkaline earth metals except which form peroxide. 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. Simple ionic models based on phenomenological pair potentials have been used to explain the global trends found in these experiments [17–20]. 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. The increasing order of the cationic size of the given alkaline earth metals is. 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. However, carbonate of lithium, when heated, decomposes to form lithium oxide. We had earlier [53, 54] concluded that the NICS(1) value is the best measure of aromaticity for benzene. The optimized M–O bond distances are slightly closer to the gas phase values than to the ionic values. The bonding is therefore primarily ionic. 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. (ii) All the alkaline earth metals form oxides of formula MO. Going to Among the candidate structures, the hexagonal-ring-based isomers and … 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. 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. 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. This increase in ZT is the direct outcome of the reduced thermal … 2) CaCl2 is widely used for melting ice on roads, particularly in very cold countries. , and For (CaO)3, however, it was found that both initial structures optimized to different geometries. In this case, three structures, namely, slab, octagonal, and ladder, were studied. (MO)5  Where M = Mg, Ca, Sr, Ba. In the case of clusters. It is gratifying to note that experimental observations of mass spectra [14, 15, 48, 55] indicate the existence and stabilities of such stacked hexagonal rings, at least for small gas-phase clusters of MgO. For (BaO)6, the inner and outer Ba–O bond distances are 2.564 Å and 2.379 Å, respectively, compared to the gas phase and bulk values of 1.940 Å and 2.762 Å, respectively. 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. This happens at the expense of the p orbital population, so that the overall charge on the metal ion remains close to +1. 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]. The temperature of decomposition i.e. In this method, negative NICS values indicate aromaticity and positive values antiaromaticity. 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). 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. 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. While the band gap for the hexagonal structure is 2.3 eV, that of the ladder structure is much smaller (1.8 eV). However, the results from such studies on alkaline earth metal oxides are contradictory and depend on the process of formation of the clusters. The calculated Mulliken charges on the metal ions are 0.930, 1.253, 0.959, and 0.943, respectively. All these carbonates decompose on heating to give CO 2 and metal oxide. It may be noted that the ring structure undergoes considerable distortion in all cases except for MgO. 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. . 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 optimized structures are rhombus shaped and planar (Figure 1). Stability of oxides decreases down the group. Alkali metal - Alkali metal - Chemical properties: Since the alkali metals are the most electropositive (the least electronegative) of elements, they react with a great variety of nonmetals. The latter three fall short of the experimental value [43] of 3.57 eV. Two conclusions, however, result from these studies. The carbonates of alkaline earth metals and Lithium carbonate decompose on heating to form oxides with the evolution of CO2. 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 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. The values of the partial charges indicate the slightly higher ionic character of (CaO)2 compared to the other (MO)2 systems. The interplanar distance in the hexagonal stacked structure (1.980 Å) is much larger than the Mg–O bond distance. The carbonates of group-2 metals and that of lithium decompose on heating, forming an oxide and carbon dioxide . For the inner metal ions, the participation of d orbitals is a little smaller. Nanocrystalline CaO is used as an absorbent to remove COD from paper mill effluent [12]. Besides, Ca2+ is approximately six times as polarizable as Mg2+, and the polarizabilities of the oxide anions are also larger in CaO because the bonding is weaker than in MgO. The additional electron comes from a 2p orbital of oxygen, and the oxygen atoms have electron configurations close to 1s22s22p5 in all cases. An explanation based on packing and aromaticity arguments has been proposed. 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. Reason : As we move down the group, the lattice enthalpy of carbonates remain approximately the same. Hence, the increasing order of the thermal stability of the given alkaline earth metal carbonates is. We find that, from (MgO)4 onward, three-dimensional structures are favored. She has started this educational website with the mindset of spreading Free Education to everyone. Therefore, the energy is lowered by keeping the oxide ions away from each other. are 0.915, 1.055, −0.952 and −0.981, respectively. , the slab structure is still the preferred one, but to a lesser extent. , whereas the opposite is true for , M = Mg, Ca, Sr, Ba and ‘Like those of the Group 1 metals, the oxides of the alkaline earths can be dissolved in water to form bases.’ ‘There are limits to such effects, however, because high concentrations of alkaline earths and the transition metal ions cause rupture of hydrogen bounds, base unstacking, and ultimately decrease of thermal stability of DNA.’ Figure 1 gives the optimized structures for all the (MO)2 moieties. 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. However, the energy differences are too small for one to make a definite statement regarding the relative stabilities. The term "thermal decomposition" describes splitting up a compound by heating it. We therefore first compared results for the MgO molecular form obtained by different methods with the experimental quantities. alkaline earth metal hydroxides are less soluble in water, basic strength of hydroxides increases down the group, preparation and properties of sulphates of alkaline earth metals, preparation of halides of alkaline earth metal, properties of halides of alkaline earth metal, properties of hydroxides of alkaline earth metals, stability and uses of alkaline earth metals, NCERT Solutions for Class 10 हिन्दी – क्षितिज – Chapter 3 – सवैया, कवित्त – देव, NCERT Solutions for Class 10 हिन्दी – क्षितिज – Chapter 2 – राम लक्ष्मण परशुराम संवाद, NCERT Solutions for Class 10 हिन्दी – क्षितिज – Chapter 1 – पद, Economics Chapter 5 Consumer Rights – Notes & Study Material. The mass spectra and collision induced fragmentation data for stoichiometric For The LDA result is far superior to the other calculations, although its tendency to overbind is clear from the result. 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. An important finding of the present study is that hexagonal tube-like structures are preferred for Solubility, thermal stability and basic character of hydroxides of alkaline earth metals increases from Mg to Ba due to increase in atomic size. (MgO)4. Peroxides are formed with increasing ease and increasing stability as the metal ions become larger. In the calculations reported in the paper, first-principles density functional (DF) calculations were performed using the DMol [5] code [33–36], available from Accelrys Inc. in the Materials Studio 3.2 package. 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. Calculated binding energies, HOMO-LUMO gaps, and Fermi energies (in eV) for (MO), Binding energies, HOMO-LUMO gaps, and Fermi energies (in eV) for (MO), Binding energies, Fermi energies, and HOMO-LUMO gaps (in eV) for (MO), Structures and Stabilities of Alkaline Earth Metal Oxide Nanoclusters: A DFT Study, Department of Chemistry, University of Delhi, Delhi-110 007, India, A. Jain, V. Kumar, M. Sluiter, and Y. Kawazoe, “First principles studies of magnesium oxide clusters by parallelized Tohoku University Mixed-Basis program TOMBO,”, N. Sharma and R. Kakkar, “Recent advancements in warfare agents/metal oxides surface chemistry and their simulant studies,”. The present calculations indicate that the vibrational frequency for this optically allowed stretching motion of oxygen atoms perpendicular to the surface of the (MgO)6 hexagonal cluster is at 691 cm−1 (intensity = 512 km mol−1), while for the slab structure, this band is at 740 cm−1 (intensity = 445 km mol−1). 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. 2) Barium meal is used to obtain a shadow of the stomach on an X-ray film which is useful in diagnosing stomach ulcers. and Oxides. The electronic density of states (DOS) near the Fermi level for the two structures is shown in Figure 7. (SrO)3. (BaO)3. For example, Li2CO3 +heat -> Li ­2 O +CO2. (CaO)4. 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. The high solubility of BeSO4 and MgSO4  is due to the high hydration enthalpy because of smaller size of Be2+ and Mg2+ ions. Li, J. R. Schlup, and K. J. Klabunde, “Fourier transform infrared photoacoustic spectroscopy study of the adsorption of organophosphorus compounds on heat-treated magnesium oxide,”, R. C. Whited, C. J. Flaten, and W. C. Walker, “Exciton thermoreflectance of MgO and CaO,”, I. S. Elfimov, S. Yunoki, and G. A. Sawatzky, “Possible path to a new class of ferromagnetic and half-metallic ferromagnetic materials,”, B. Nagappa and G. T. Chandrappa, “Nanocrystalline CaO as adsorbent to remove COD from paper mill effluent,”, F. Jin, Y. Liu, and M. D. Christopher, “Barium strontium oxide coated carbon nanotubes as field emitters,”, W. A. Saunders, “Structural dissimilarities between small II-VI compound clusters: MgO and CaO,”, W. A. Saunders, “Molecules and clusters,”, T. P. Martin and T. Bergmann, “Mass spectra of Ca-O and Ba-O clusters,”, P. J. Ziemann and A. W. Castleman, “Mass-spectrometric study of the formation, evaporation, and structural properties of doubly charged MgO clusters,”, P. J. Ziemann and A. W. Castleman, “Structures and bonding properties of calcium oxide clusters inferred from mass spectral abundance patterns,”, P. J. Ziemann and A. W. Castleman Jr., “Mass spectrometric study of MgO clusters produced by the gas aggregation technique,”, P. J. Ziemann and A. W. Castleman Jr., “Stabilities and structures of gas phase MgO clusters,”, M. Gutowski, P. Skurski, X. Li, and L.-S. Wang, “, R. Kakkar, P. N. Kapoor, and K. J. Klabunde, “Theoretical study of the adsorption of formaldehyde on magnesium oxide nanosurfaces: size effects and the role of low-coordinated and defect sites,”, R. Kakkar, P. N. Kapoor, and K. J. Klabunde, “First principles density functional study of the adsorption and dissociation of carbonyl compounds on magnesium oxide nanosurfaces,”, R. Dong, X. Chen, X. Wang, and W. Lu, “Structural transition of hexagonal tube to rocksalt for (MgO), M. Srnec and R. Zahradník, “Small group IIa-VIa clusters and related systems: a theoretical study of physical properties, reactivity, and electronic spectra,”, M. Wilson, “Stability of small MgO nanotube clusters: predictions of a transferable ionic potential model,”, M. Wilson, P. A. Madden, N. C. Pyper, and J. H. Harding, “Molecular dynamics simulations of compressible ions,”, E. De La Puente, A. Aguado, A. Ayuela, and J. M. López, “Structural and electronic properties of small neutral (MgO), M.-J. Oxo salts of alkaline metals are more stable than the alkaline earth metal oxosalts because it have small cations . The researchers substituted other alkali or alkaline earth metals like barium, strontium and calcium in the place of sodium. The melts of alkali metal hydroxide—nitrate systems are thermally stable to at least 300°C above the melting temperatures. The calculated NICS(1) value for benzene is −10.84, whereas the corresponding values for (MgO)3 and (CaO)3 ring structures are −2.05 and 2.75, respectively, clearly indicating that the MgO ring is about 20% aromatic, while the CaO ring is antiaromatic, accounting for the increased stability of the MgO ring. Be > Mg > > Ca > Sr > Ba. As the cluster size increases, the bond lengths and binding energies increase in an oscillatory manner. In the case of MgO, both LDA and GGA predict that the most stable structure is the chair form. Theoretical work on ionic materials has been centered mostly in the family of alkali metal halides, and studies of metal oxide clusters have been comparatively scarce, despite their importance in many branches of surface physics, such as heterogeneous catalysis or corrosion. 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. Among the candidate structures, the hexagonal-ring-based isomers and the slab shapes are found to display similar stabilities. PROPERTIES. All the alkaline earth metals form carbonates (MCO 3). While this observation is important as such and contradicts the exclusive nature of the latter structural shapes proposed previously [17–20], it is noteworthy how the stability ordering changes as the metal atomic number increases among the alkaline earth elements. The calculated vibrational frequencies are 751 cm−1 (LDA) and 719 cm−1 (GGA), in comparison with the observed [43] value of 785 cm−1. M + 2C → MC 2 MC 2 + 2H 2 O → M (OH) 2 + C 2 H 2 For This leads us to believe that it is a packing effect rather than an electronic one. The bond lengths and total energy per molecule for the lowest energy structures are given in Table 5. 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°. Their structures are usually inferred indirectly from the mass spectra of ionized clusters, the more abundant species being interpreted as the more stable. carbonates of alkali metals and NH, Alkaline earth metal nitrates are prepared in solution and can be crystallized as hydrated salt by the action of HNO, All nitrates are soluble in water and decompose on heating to give the corresponding oxides with evolution of NO. The bond length is elongated to 1.882 Å in the most favorable structure of (MgO)2, which is a rhombus. (ii) All the alkaline earth metals form oxides of formula MO. Bulk MgO is relatively inert, but its reactivity is greatly enhanced in the nanoscale. The terminal Ca–O bond distance in the three-ring stack is observed to be the mean of the 2.405 Å lattice value and the molecular 1.822 Å distance [43]. bond (2.450 Å) with a bond order of only 0.397. The energy differences are higher for this case, and the slab form is more emphatically preferred. 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. These metals are known as alkaline earth metals as their oxides are alkaline and occur in earth crust. It is well known that (MgO)3 ring structures are competitive building blocks in the growth of very small MgO clusters [29]. Two distinctly different interplanar distances (1.936 Å and 1.898 Å) are also observed, depending on which atom, Mg or O, sits on the terminal ring of the three-ring stack. All the Group 2 carbonates and their resulting oxides exist as white solids. 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). Carbides react with water to liberate acetylene gas and hence used as a source for the gas. The effect of heat on the Group 2 carbonates All the carbonates in this group undergo thermal decomposition to the metal oxide and carbon dioxide gas. 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 : The sulphates of alkaline earth metals decompose on heating giving their corresponding oxides and SO3. The bond orders are 0.837 and 0.610, respectively. The hydration enthalpies of the metal cation decreases from Be2+ to Ba2+ . 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. 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°). , our results that ring structures lie higher in energy are in contrast with reported results [17–20], in which The fact that a small cation can stabilize a small anion and a large cation can stabilize a large anion explains the formation and stability of these oxides. 2Ca + O 2 → 2CaO. Thus, hexagonal rings are slightly more stable than the slab-shaped structures in the case of 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. The cores of Ba2+ and Sr2+ were treated with the all-electron approach. Our calculations employed numerical basis sets of double-ζ quality plus polarization functions (DNP) to describe the valence orbitals. In this figure, as well as all other figures, the metal ions are represented by green balls and the oxide ions by red balls. 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. Author of this website, Mrs Shilpi Nagpal is MSc (Hons, Chemistry) and BSc (Hons, Chemistry) from Delhi University, B.Ed (I. P. University) and has many years of experience in teaching. Our earlier studies [22, 23] on the (MgO)12 cluster had indicated that the (MgO)12 nanotube, consisting of four stacked hexagonal (MgO)3 rings, is more stable than the bulk-like cubic structure by 0.48 eV. 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. Thermal stability: - Carbonates: - The carbonates of alkali metals except lithium carbonate are stable towards heat. 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. The carbonates of alkali metals except lithium carbonate are stable to heat. The group replaced the sodium by other alkali or alkaline earth metals: calcium, strontium, and barium. In this case, three structures, namely, slab, hexagonal, and ladder, were studied (Table 4). BeSO4 and MgSO4 are highly soluble, CaSO4 is sparingly soluble but the sulphates of Sr, Ba and Ra are insoluble. Table 2 gives the calculated energies and the HOMO-LUMO gaps for the various structures. For CaO, the slab structure is again preferred. As noted previously, the preferred geometry for the (MgO)6 cluster is tubular, which becomes more stable than the rectangular bulk-like cluster due to stabilization of the occupied levels. These are shown in Figure 8. The atomic and ionic radii of O and lattice O2− are 0.66 and 1.40 Å, respectively. (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. Hypothesis for the ZT improvement of layered cobalt oxide. 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. Thermal stability: Increases down the group like carbonates BeSO 4