Water is a common substance
 Properties are very unique and unusual
 Only substance on Earth that exists in large
quantities in all three states of matter
There are 6!
1- Low density as a solid
 most substances are denser as solids than liquids, but
water is an important exception.
 Water is less dense as a solid, and this is the reason
that ice floats in liquid water rather than sinking.
 Water achieves its maximum density at 4°C and since
freezing point is O°C, it has lower density as ice than
liquid water.
2- Polar bonds
 bond where the electrons are shared unequally
 Like a MAGNET – positive end and negative end
 Just like a magnet, opposite ends can attract each other
 Polar molecules can bond with other polar molecules,
but CAN NOT bond with non-polar molecules (just like
magnets won’t stick to non-magnetic objects)
 Water is known as the universal solvent because water
can dissolve most substances due to its polarity.
Positive
Negative
3- Hydrogen bonding
 Water likes to make weak bonds with other water
molecules by Hydrogen Bonding. Opposite ends of
the molecules attract!
4- High Boiling Point
 The intermolecular hydrogen bonds hold the water
molecules together strongly enough that they cannot
readily escape into the gaseous states at ordinary
temperature.
 In order for water to boil, the temperature must be
increased, adding enough energy to overcome the
hydrogen bonds that are holding the water molecules
together.
 And this is why water has a high boiling point, 100°C.
5- High Surface Tension
 Surface tension: the force needed to overcome
intermolecular attractions (hydrogen bonds) and
break through the surface of a liquid or spread the
liquid out.
 Water has high surface tension, which means it tends
to clump together in drops rather than spread out in a
thin film.
 Cohesion: water molecules like to stay closely together
(water molecules like to stick to water molecules)
6- Capillary action
 Adhesion: water molecules are attracted and stick to
other substances
 Capillary action is the rising of a liquid in a narrow
tube; this occurs due to competition with the
interparticle attractive forces between the molecules
and the attractive forces between the water and the
tube that contains it.
Phase Changes
 Solid to liquid = Melting
 Liquid to solid = Freezing
 Liquid to gas =
Evaporating/Boiling
 Gas to liquid = Condensing
 Solid to gas = Sublimation
 Gas to solid = Deposition