Water

Water has the highest specific heat of any common substance, 1 calorie/gm °C = 4.186 J/gm °C. This provides stability of temperature for land masses surrounded by water, provides stability for the temperature of the human body, makes it an effective cooling agent, and many other benefits. The high heat of vaporization of water makes it an effective coolant for the human body via evaporation of perspiration, extending the range of temperatures in which humans can exist. 水是所有常见物质中比热最高的，1 卡/克·摄氏度 = 4.186 焦/克·摄氏度。这为被水包围的陆地提供了温度稳定性，为人体温度提供了稳定性，使其成为一种有效的冷却剂，并有许多其他好处。水的高汽化热使其通过汗液蒸发成为人体的有效冷却剂，扩展了人类可以存在的温度范围。

At right is a scale model of a water molecule based on the experimental bond length and angle in the gas phase from spectroscopic data. The sizes of the spheres representing the atoms are scaled from their covalent radii in the periodic table. While the numbers for the angle and bond length represent the high precision of gas-phase spectroscopy of isolated molecules, it is not to be presumed that water molecules are rigidly locked into that configuration. They are in ceaseless rotation and vibration in addition to the high linear speeds associated with thermal energy at ordinary temperatures. 右侧是基于气相光谱数据中测定的键长和键角的水分子比例模型。模型中代表原子的球体大小是根据元素周期表中的共价半径进行缩放的。虽然键角和键长的数值反映了气相光谱学对孤立分子的高精度测量，但不能据此认为水分子被严格固定在该构型中。实际上，水分子在常温下持续进行旋转和振动，此外还伴随着与热能相关的高速运动。

In general, molecular vibrational motion takes place on a shorter time scale than rotation, going through many cycles of vibration during a rotation period so that the bond lengths obtained from molecular rotation spectra are effective average bond lengths. The parameters of the isolated water molecule above are altered significantly in liquid water and even more in hexagonal ice crystals. Water molecules have large dipole moments and the resulting hydrogen bonding in the liquid state alters the bond angle to something like 105.5 to 106° with a bond length around 0.097 nm. In hexagonal ice crystals, the bond angle approaches the tetrahedral angle, 109.47 °. In addition to all the molecular motions, in liquid water there is a continuous exchange of hydrogens between water molecules - about one exchange per millisecond at a neutral pH of 7.0 and more rapidly when the pH departs from neutrality.

Water provides the standard for density at 1 gram/cm³.

While water may seem to be an ordinary liquid, its properties are in many ways unusual. The changes in the properties of water near its freezing point are illustrated below with sketches adapted from Debenedetti and Stanley. The vertical scales are exaggerated for emphasis - the actual magnitudes of the changes are quite small. It is the contrast with the properties of other liquids which makes them remarkable.

Water references:

Franks, F., Water: A Matrix of Life, 2nd Ed., Royal Society of Chemistry,Cambridge, UK (2000).

Ball, P., Life's Matrix: A Biography of Water, Farrar, Straus, and Giroux, New York (2000).