why is sef4 melting point higher than sef6?
due to different exposion towards heat
Honore I don't understand...
The melting point of a compound is influenced by several factors, including the strength and type of intermolecular forces between its molecules. In the case of SEF₄ and SEF₆, both are covalent compounds containing fluorine and selenium.
To understand why SEF₄ has a higher melting point than SEF₆, we need to examine their molecular structures and intermolecular forces.
SEF₄ (selenium tetrafluoride) has a tetrahedral molecular structure with fluorine atoms bonded to a central selenium atom. Each fluorine atom is positioned around the selenium atom, forming a four-sided pyramid shape. In SEF₄, the selenium atom also has two pairs of lone electrons. The electron pair repulsion theory predicts that the lone pairs will position themselves opposite each other, distorting the tetrahedral shape.
Due to the polarity of the selenium-fluorine bonds in SEF₄, there are strong dipole-dipole interactions between neighboring molecules. These dipole-dipole forces, also known as van der Waals forces, contribute to the higher melting point of SEF₄ compared to SEF₆.
On the other hand, SEF₆ (selenium hexafluoride) has an octahedral molecular structure with six fluorine atoms arranged around a central selenium atom. Unlike SEF₄, SEF₆ does not possess any lone pairs on the selenium atom. Therefore, SEF₆ has a symmetrical molecular structure.
The absence of lone pairs in SEF₆ reduces the dipole-dipole interactions between neighboring molecules, resulting in weaker van der Waals forces. Consequently, SEF₆ has a lower melting point compared to SEF₄.
In summary, the difference in melting points between SEF₄ and SEF₆ can be attributed to the differences in their molecular structures and the strength of the intermolecular forces, particularly the dipole-dipole interactions caused by the polarity of the selenium-fluorine bonds.