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I'm learning about ionic bonding and polarizability. Larger anions with higher charge should make more polarized ionic bonds. $\ce{O^2-}$ is both larger and has higher charge than $\ce{F^-}.$

So, why does $\ce{WO3}$ have a melting point of $\sim\pu{1473 °C}$ and $\ce{WF6}$ have a melting point of $\sim\pu{17 °C}?$

I should add that ionic compounds usually have higher melting point than the covalent ones, which makes it strange that $\ce{WF6}$ is the one with the lowest melting point, as I would think that to have the most ionic bond.

andselisk
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    Both are better understood as mostly covalent. – Ivan Neretin Jan 05 '21 at 18:40
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    Same reason why SiO2 is solid and SiF4 gas. – Mithoron Jan 05 '21 at 20:56
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    https://chemistry.stackexchange.com/questions/16261/metal-compounds-that-bond-covalently – Mithoron Jan 06 '21 at 02:40
  • Is it really reliable to always consider ionic compounds to have higher melting point than covalent? Diamond is covalent but has a melting point of above 7000°F(in absence of oxygen)[https://www.nationalgeographic.org/media/diamonds-arent-forever-wbt/#:~:text=In%20the%20absence%20of%20oxygen,Celsius%20(7%2C280°%20Fahrenheit).]. I would direct this question to @Ivan Neretin but eager to learn more if anyone else wants to contribute too? – Desai Jan 06 '21 at 02:43
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    There are molecular compounds, and then they are covalent crystals. Both are covalent, but very, very different in other regards. – Ivan Neretin Jan 06 '21 at 11:59

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