Hóa đại cương Tôi có thắc mắc, mong các bạn chỉ giúp : 1/ So sánh nhiệt độ nóng chảy của BaSO4, CaSO4 Theo các bạn thì nên sử dụng tác dụng phân cực của ion dương hay dựa vào năng lượng mạng tinh thể ? Đối với các hợp chất ion đơn giản như NaF, NaCl... thì việc sử dụng 2 cách này đều cho kết quả giống nhau. Nhưng khi làm cho bài này thì kết quả trai ngược nhau. Tôi nghĩ do kích thước quá lớn, việc sử dụng tác dụng phân cực không còn được chính xác nữa. Theo tôi, do bk Ca2+ > Ba2+ nên lực hút giữa các ion trong CaSO4 > BaSO4 nên CaSO4 có NĐNC cao hơn. 2/ Để có được một lk phối trí, một nguyên tử phải dư đôi điện tử tự do và một nguyên tử phải còn orbitan hóa trị trống. Vậy trong TH HClO2 : H-O-Cl_O : Cl_O là 1 lk phối trí với nguyên tử Cl cung cấp một đôi điện tử, nhưng O đâu còn orbitan hóa trị trống để mà nhận ? Cám ơn các bạn nhiều.
(1) From what I have learned, crystalline materials with high lattice energy tend to have high melting point. And by the way, barium sulfate has a higher melting piont (1580''C) compared to that of CaSO4 (1460''C) (not the other way around like you have mentioned). I am not sure if you can use the difference in the polarizability of Ca2+ and Ba2+ to compare the melting points of CaSO4 and BaSO4. However, I found the argument you have presented incorrect. In the example of NaF and NaCl, the cations are the same but the fluoride ion is much smaller than the chloride ion. Therefore, chloride ion can BE POLARIZED easily compared to fluoride ion, and one would predict that the melting point of sodium fluoride is higher. (This is true in reality.) For CaSO4 and BaSO4, the cations are different. Since Ca2+ is smaller, it can POLARIZE the sulfate ion more easily. And again, the conventional wisdom predicts a higher melting point for BaSO4 (which is also true in reality). So, unlike what you have suggested, I do not find any contradiction here. (2) The electronic configuration of oxygen is (He) 2s2 2p4. Hund rules are applied to electrons in the ground state only. They do not prevent electrons from obtaining a different configuration during excitation which is what happens during chemical reactions. When four p-electrons are paired up, one empty p-orbital is available. I hope this helps and I am sorry about my poor English.
(1) From what I have learned, crystalline materials with high lattice energy tend to have high melting point. And by the way, barium sulfate has a higher melting piont (1580''C) compared to that of CaSO4 (1460''C) (not the other way around like you have mentioned). I am not sure if you can use the difference in the polarizability of Ca2+ and Ba2+ to compare the melting points of CaSO4 and BaSO4. However, I found the argument you have presented incorrect. In the example of NaF and NaCl, the cations are the same but the fluoride ion is much smaller than the chloride ion. Therefore, chloride ion can BE POLARIZED easily compared to fluoride ion, and one would predict that the melting point of sodium fluoride is higher. (This is true in reality.) For CaSO4 and BaSO4, the cations are different. Since Ca2+ is smaller, it can POLARIZE the sulfate ion more easily. And again, the conventional wisdom predicts a higher melting point for BaSO4 (which is also true in reality). So, unlike what you have suggested, I do not find any contradiction here. (2) The electronic configuration of oxygen is (He) 2s2 2p4. Hund rules are applied to electrons in the ground state only. They do not prevent electrons from obtaining a different configuration during excitation which is what happens during chemical reactions. When four p-electrons are paired up, one empty p-orbital is available. I hope this helps and I am sorry about my poor English.
And by the way, for the comparison in (1) using the polarizability of ions, the two materials need to have the same crystal structure. Otherwise, the comparison is meaningless.
And by the way, for the comparison in (1) using the polarizability of ions, the two materials need to have the same crystal structure. Otherwise, the comparison is meaningless.
