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AlF_3和SiF_4是元素周期表中第三周期相邻两种元素的氟化物,通常情况下,AlF_3呈固体状态,熔点为1257℃,而SiF_4呈气体状态,熔点为-90℃。造成AlF_3和SiF_4之间熔点甚大差异的原因是什么呢? 一般可能会认为是由于它们的化学键从极端的离子型突变成极端的共价型所致。但事实上,AlF_3中的键在性质上和SiF_4中的键只有微小的差异,这可从下表所列的有关数据看出:
AlF_3 and SiF_4 are the fluorides of the adjacent two elements in the third period of the periodic table. Generally, AlF_3 is in a solid state with a melting point of 1257 ° C while SiF_4 is in a gaseous state with a melting point of -90 ° C. What causes the large melting point difference between AlF_3 and SiF_4? It may generally be attributed to their chemical bond transition from extreme ionic to extreme covalent. However, in fact, the bonds in AlF_3 are slightly different in nature from the bonds in SiF_4, as can be seen from the relevant data listed in the following table: