Water

1
Water Bonding
2
Waters Atoms

• Oxygen
• 8 protons, positively charged particles in the
  nucleus
• 8 electrons, negatively charged particles in the
  outer shell.
• First orbital is full and the second orbital
  could hold 2 more electrons

3

• Hydrogen
• 1 proton, positively charged particles in its
  nucleus
• 1 electron, negatively charged particles in its
  outer shell.
• This outer shell could hold 2 electrons.

4
Molecules That Form Water

• Molecular Oxygen
• 2 oxygen atoms share
• 4 electrons to fill their
• orbitals
• Molecular Hydrogen
• 2 hydrogen atoms
• share 2 electrons to
• fill their orbital.

Sharing electrons covalent bonding
5
A Water Molecule

• Molecule has no net charge
• Oxygen end ? slight negative charge
• Hydrogen end ?slight positive charge
• The regions of differing charge have to do with
  bonding between the atoms

Analogy Water is like a magnet. Both water and
magnets have oppositely charged poles
6
Covalent Bonds

• A covalent bond ? 1, 2 or 3 electrons are shared
  b/w atoms
• Polar covalent bond ? electrons are shared
  unequally.
• One atom exerts a slightly greater pull on the
  shared electrons resulting in regions of positive
  and negative charge.
• Example H2O
• Nonpolar covalent bond ? electrons are shared
  equally.
• No net charge and no regions of differing charges
• Example fats, oils, waxes (lots of C-H bonds)

7
Bonds in a Water Molecule

• The bonds inside water are polar covalent bonds

8
Hydrogen Bonds

• Hydrogen bonds form at hydrogen atoms that are
  already covalently bonded in a molecule .
• The hydrogen atoms slight negative charge weakly
  attracts an atom that is already covalently
  bonded to something else.
• Hydrogen bonds form between water molecules and
  many other important biological molecules such as
  DNA and proteins.

9
Hydrogen Bonds b/w Water Molecules
10
Ionic Bonds

• Ionic bonds ? bonds between ions of opposite
  charge.
• An ion ? atom that loses or gains one or more
  electrons.

11
Hydrophilic Substances

• Polar molecules (like water) have slight opposite
  charges at opposite end of the molecule
• Polar substances are attracted to the water
  molecules because they can easily form hydrogen
  bonds with water molecules.
• Because of their polar nature, these substance
  easily dissolve in water and are called
  hydrophilic or water loving

Remember Water and other polar substances are
like magnets. They have areas (or poles) of
opposite charge. Polar substances mix or
dissolve because the areas of opposite charge
interact.
12
Hydrophobic Substances

• Nonpolar ? do NOT have opposite charges at
  opposite ends of the molecule same charge
• The polarity of water repels nonpolar substances.
  These nonpolar substances do not dissolve in
  water and are called hydrophobic or water
  dreading substances.

Hydrophobic substances are not like magnets.
They have no charge or no poles. They do not mix
or dissolve in water because there is no
interaction between opposite charges.
13
Waters Life-Giving Properties

• Water has properties which make it essential for
  life on Earth.
• Properties are due to waters
• Polar nature
• Hydrogen bonding between water molecules
• Hydrogen bonding and ionic bonding with other
  polar substances.

14
Summary of Properties of Water

• Bonds to hydrophilic substances
• Repels hydrophobic substances
• Stabilizes temperature
• Is cohesive
• Has capacity to dissolve substances

15
Waters Temperature-Stabilizing Effect

• Compared to other fluids, water absorbs much more
  heat before it gets hotter.
• What happens when water is heated?
• Energy input increases temperature which is the
  measure of molecular motion. This causes
  hydrogen bonds between water molecules to break
  and water to evaporate. Evaporation uses energy
  and cools the surface of the water.

16
Water is Less Dense as a Solid

• What happens when water freezes?
• Below 0 degrees Celsius, hydrogen bonds between
  water molecules resist breaking and ice forms.
  Ice is less dense than water and floats on the
  surface creating a blanket that insulates the
  water below.
• Water is most dense at 4 degrees Celsius

17
Waters Solvent Properties

• Water is an excellent solvent. Ions and other
  polar molecules dissolve easily in it due to the
  polar nature of water.

Na
Cl-
18
Waters Cohesion

• Cohesion is having the capacity to resist
  breaking when stretched or under tension.
• Hydrogen bonds b/w water exert a continuous pull
  on individual molecules causing them to stick
  together.
• Ex Helps water move up the stem of a plant,
  against gravity