Скачать или смотреть Why Does Ice Float? Why is that Amazing? - [2]

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In this lesson, you will learn why ice floats on liquid water. In order to understand this, we must first understand that the water molecule, H2O, is a bent polar molecule. It is bent because the hydrogens are not in a straight line with the oxygen. Polar means that half of the molecule has a negative charge while the other half has a positive charge. The charged nature of the water molecule is due to the nature of the electronegativity of the oxygen atom. It pulls in the covalently bonded electrons closer than the hydrogen. Because of this, oxygen is slightly negative and hydrogen is slightly positive. When water cools down, the attractive nature of adjacent molecules becomes dominant and ice is then locked into a crystal lattice that is larger than the spacing of the molecules in the liquid state. The ice expands as it freezes - this makes it less dense than water and so water ice floats on water. This means that all ponds and streams freeze from the top down, enabling life to flourish because the ice acts as an insulator, protecting the liquid water underneath.