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Discuss how the unique physical and chemical properties of water contribute to the importance of water for life on Earth to survive.

Water is found all throughout nature, and is a necessary component in nearly all organic reactions. It is the most abundant compound on the surface of the planet. The majority of water on Earth is sea water, and water is also present as solid ice and invisible gaseous clouds. All life on Earth requires water to survive, and it is speculated that extraterrestrial water may be a sign of life (or at least a precursor to life) elsewhere in the universe. Along with enabling life, water has an effect on non-living things, such as its weathering and erosion of rocks and soil. Water also acts as a heat sink, absorbing excess heat and buffering the Earth's temperature from extreme changes. Water is a vital part of any living system, from entire habitats down to individual cells. So what is water?

Chemical Properties of Water

Water (also known as H2O) is a polar chemical compound containing one oxygen (O) atom and two hydrogen (H) atoms (as seen in the first figure.) These three atoms are bound together with covalent bonds, meaning they share their pairs of valence or outer electrons together. Each hydrogen atom is separately bound to the central oxygen atom and the oxygen also has two pairs of unshared electrons, giving one water molecule a total of four shared and four unshared valence electrons. Water molecules have a bent shape, with a 104.45° angle between the two hydrogen’s.

Despite sharing their electrons, water molecules are polar because the valence electrons are shared unequally between the oxygen and hydrogen atoms. Oxygen has a greater electro negativity than hydrogen does, meaning it is highly attracted to electrons, so it pulls more strongly on the shared electrons and keeps them closer to itself. This creates a dipole moment, i.e., two electrical poles. This unequal sharing of electrons means that the electrons' negative charges cluster at the oxygen end of the molecule, leaving the hydrogen end of the molecule to be partially positive while the oxygen end is partially negative. Water's polarity leads to it being adhesive to many other substances, and helps make it an excellent solvent.

Polar substances dissolve well in water as "like dissolves like," but nonpolar substances do not dissolve as readily (or at all.) A common example of this solubility is the dissolution of table salt (NaCl) into water to produce Na+ and Cl- ions surrounded by water molecules with their positive and negative poles oriented towards or away from the ions depending on the ion's charge. When a polar solute such as a salt dissolves into positive and negative ions, the water molecules orient themselves to surround the individual ions and point their corresponding poles at the ion based on its charge; water's negative poles point at positive ions and