Properties of Water
 Why does ice float?
A. Because it evaporates at 100°C
B. Because it forms pockets of
empty space when frozen
C. Because it is a universal solvent
D. Because it melts at 0°C
 Which best describes the
movement of water molecules in a
glass of liquid water?
A. The molecules all move at the same
speed
B. The molecules all move at different
speeds
C. The molecules are not moving
D. The molecules only move when you
move the glass of water.
Think pair share
 Do you know what the term polar
means?
 How do you think polar relates to
molecules?
What is water?
 Think-Pair-Share with your table mates to
answer the questions below
 What is the chemical formula for water?
 What does the formula tell us about water?
 What kind of chemical bond do you think
water has?
What water is made of… H2O
Stop at 3 min 50 sec.
Video notes
 Electrolysis breaks water apart into
 2 parts hydrogen and 1 part oxygen
Water’s covalent bonds
 Sometimes in covalent bonds there is an
unequal sharing of electrons in a molecule.
 When this happens, atoms pull more strongly on
the shared electrons than other atoms do.
 As a result the electrons move closer to one
atom, causing atoms to have slight
electrical charges.
 One side of the molecule is slightly negative and
the other is slightly positive
Polar Molecules
- Molecules with unequal electron sharing are
called polar molecules
- Polar molecules have a strong attraction to
one another because of their slightly charged
sides.
- (just like opposite ends of a magnet)
Are all covalent bonds polar?
 Not all covalently bonded elements are polar,
only the ones with unequal sharing.
 A molecule can be nonpolar if…
 it contains positive and negative charges that
cancel each other out
A polar molecule
Water is a polar molecule and looks like
this…
Electrons are pulled more towards
the nucleus of the oxygen
Polar molecule video
Video notes
 The attraction atoms have for electrons
varies.
 Polar molecules have positive and
negative poles like a battery or a
magnet.
Why does it matter that water
is polar?
 Water’s charged sides attract other
elements and compounds with their charges.
 For example:
a negative ion like chlorine would be attracted to
the positive end of a water molecule (the H or
hydrogen side)
Water the Universal solvent
 The polar charge that develops across the
water molecule helps make it an excellent
solvent.
 Solvent- a liquid that allows solids to break apart
to become a well mixed solution.
 This is why water is called the Universal
Solvent.
 Water can dissolve more substances than any
other liquid
Salt (NaCl) dissolved in water
Salt contains sodium ions Na+ and chlorine ions ClSodium is attracted to oxygen end of H2O
Chlorine is attracted to hydrogen end of H2O
this can also be seen on pg 180 of your textbook
CLICK HERE FOR SALT WATER ANIMATION