Chemistry - covalent molecules

2008-05-08 5:02 pm

The elements carbon and silicon have much in common. There are four electrons in the outer shell in each of the atoms. Both form a dioxide. But, while carbon dioxide is gas at room temperature, silicon dioxide has the very high melting temperature of 1700 degree(C). Explain this significant difference in terms of their structure.

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回答 (1)

Uncle Michael

2008-05-08 6:27 pm

✔ 最佳答案

The melting point and boiling point of carbon dioxide are low. This is because carbon dioxide has simple molecular structure, in which the carbon dioxide molecules are held together by weak van der Waals’ forces (weak intermolecular forces).

圖片參考：http://www.geocities.com/davidlvessell/3d_co2.gif

The melting point and boiling point of silicon dioxide are high. This is because silicon dioxide has giant covalent structure, in which the silicon and oxygen atoms are held together by a network of strong covalent bonds.

圖片參考：http://volga.eng.yale.edu/sohrab/grouppage/pics/SiO2bulksupercell_thumb.jpg

參考: http://www.geocities.com/davidlvessell/3d_co2.gif; http://volga.eng.yale.edu/sohrab/grouppage/pics/SiO2bulksupercell_thumb.jpg

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