量子力學問題 為何水是透明的

因為水是純物質例如向紅茶 不是透明的因為它是茶葉+水所以是混合物所謂透明就是只有1種物質所組成的再舉例 養樂多養樂多的成分有益菌+水+糖而混合物就是2種以上合起來的物質所以純物質 就是1種物質所組成的...

Why some materials, like water and ice, glass etc, are transparent is a macroscopic phenomenon (宏觀現象). It can be well explained by classical electromagnetic theory (電磁理論). Quantum mechanics mainly deals with microscopic phenomena of atmic or sub-atomic scale. Hence, it is not approriate to use quantum mechanics to explain the degree of transparency of materials, which involves the degree of absorption of electromagneic waves in those materials.

The following web-page gives an explanation why water and glass are transparent to light (which is of electromagnetic in nature).

http://education-portal.com/academy/lesson/transparent-and-opaque-materials-in-electromagnetic-waves.html#lesson

The following is a relevant excerpt from the web-page:

When a light wave strikes the surface of the glass, it sets the electrons vibrating at a certain frequency. This frequency is not the resonant frequency of the glass. The vibrations pass from the surface atoms to the neighboring atoms and then on to more atoms through the bulk of the glass. The frequency doesn't change when the vibrations pass from one atom to another. Once this energy gets to the other side of the glass, it is re-emitted from the opposite surface. The light wave effectively passes through the glass unchanged. As a result, we can see straight through the glass, almost as though it isn't even there. Transparency thus occurs because of the transmission of light waves through the bulk of an object.

水是氫氧化合物，即是氫氣及氧氣組成(H2O)。
氫氣與氧氣都同樣是透明物質，因此水亦應該是透明。以上純是講笑答案，用以解答樓主的問題。因為在化學上，這不是必然的現象。

2014-12-20 22:04:06 補充：
在化學上，酸、鹼混合就會產生PPT。
舉例如石灰水(鹼性)，透明顏色；當混合碳酸水(亦是透明)，就會變成奶白色。

你強調是"量子力學"考慮，我估是要在原子結構去考慮而已。