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Water

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Water & Bonding Water s Atoms Oxygen 8 protons, positively charged particles in the nucleus 8 electrons, negatively charged particles in the outer shell. – PowerPoint PPT presentation

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Title: 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
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