Water is a chemical compound with the chemical formula H
2O. A water molecule contains one oxygen and two hydrogen atoms that are connected by covalent bonds. Water is a liquid at standard ambient temperature and pressure, but it often co-exists on Earth with its solid state, ice, and gaseous state, steam (water vapor).
2O. A water molecule contains one oxygen and two hydrogen atoms that are connected by covalent bonds. Water is a liquid at standard ambient temperature and pressure, but it often co-exists on Earth with its solid state, ice, and gaseous state, steam (water vapor).
water, odorless, tasteless, transparent
liquid that is colorless in small amounts but exhibits a bluish tinge in
large quantities. It is the most familiar and abundant liquid on earth.
In solid form (ice) and liquid form it covers about 70% of the earth's
surface. It is present in varying amounts in the atmosphere. Most of the
living tissue of a human being is made up of water; it constitutes
about 92% of blood plasma, about 80% of muscle tissue, about 60% of red
blood cells, and over half of most other tissues. It is also an
important component of the tissues of most other living things.
Structure of the Water Molecule
Many of the physical and
chemical properties of water are due to its structure. The atoms in the
water molecule are arranged with the two HO bonds at an angle of about
105° rather than on directly opposite sides of the oxygen atom. The
asymmetrical shape of the molecule arises from a tendency of the four
electron pairs in the valence shell of oxygen to arrange themselves
symmetrically at the vertices of a tetrahedron around the oxygen
nucleus. The two pairs associated with covalent bonds (see chemical bond)
holding the hydrogen atoms are drawn together slightly, resulting in
the angle of 105° between these bonds. This arrangement results in a
polar molecule, since there is a net negative charge toward the oxygen
end (the apex) of the V-shaped molecule and a net positive charge at the
hydrogen end. The electric dipole gives rise to attractions between
neighboring opposite ends of water molecules, with each oxygen being
able to attract two nearby hydrogen atoms of two other water molecules.
Such hydrogen bonding, as it is called, has also been observed in other
hydrogen compounds. Although considerably weaker than the covalent bonds
holding the water molecule together, hydrogen bonding is strong enough
to keep water liquid at ordinary temperatures; its low molecular weight
would normally tend to make it a gas at such temperatures.
Various
other properties of water, such as its high specific heat, are due to
these hydrogen bonds. As the temperature of water is lowered, clusters
of molecules form through hydrogen bonding, with each molecule being
linked to others by up to four hydrogen bonds, each oxygen atom tending
to surround itself with four hydrogen atoms in a tetrahedral
arrangement. Hexagonal rings of oxygen atoms are formed in this way,
with alternate atoms in either a higher or lower plane than their
neighbors to create a kinked three-dimensional structure.
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