范德华半径

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本條目仍然有文字尚未被翻譯成中文，條目是根據英語維基百科進行翻譯。
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元素	半徑 (埃)
氫	1.20
碳	1.7
氮	1.55
氧	1.52
氟	1.35
磷	1.9
硫	1.85
氯	1.8

范德华半径(van der Waals radius)，在晶体中，相鄰的兩原子沒有鍵結，而是以分子间范德华力互相吸引，加上原子間本身的排斥力交互作用，其核間最適距離可用來指定該半徑，如氖之相鄰兩原子核间平均距離為320pm，其值的一半160pm即為凡得瓦半徑。

一些非中文的文字因为尚未翻譯而被隐藏，歡迎參與翻譯。

Real gases do not behave exactly as predicted. In some cases the deviation can be extremely large. For example, ideal gases could never become liquids or solids, no matter how much they were cooled or compressed. Modifications of the ideal gas law, $P\tilde{V} = nRT$ , were therefore proposed. Particularly useful and well known is the van der Waals equation of state: $\left (P + a(\frac{n}{\tilde{V}})^2\right ) (\tilde{V} - nb) = nRT$ , where a and b are adjustable parameters determined from experimental measurements carried out on actual gases. Their values vary from gas to gas.

The van der Waals equation also has a microscopic interpretation. Molecules interact with one another. The interaction is strongly repulsive at very short distance, becomes mildly attractive at intermediate range, and vanishes at long distance. The ideal gas law must be corrected when attractive and repulsive forces are considered. For example, the mutual repulsion between molecules has the effect of excluding neighbours from a certain amount of territory around each molecule. Thus, a fraction of the total space becomes unavailable to each molecule as it executes random motion. In the equation of state, this volume of exclusion (nb) should be subtracted from the volume of the container (V), thus: (V - nb). The other term that is introduced in the van der Waals equation, $a(\frac{n}{\tilde{V}})^2$ , describes a weak attractive force among molecules, which increases when n increases or V decreases and molecules become more crowded together.