Transcript Ch9 Diatomic water chem cj

Ch. 9—Covalent Bonding and Diatomic
Molecules
Journal pg 29, book page 241…
Octet rule—atoms gain, lose, or share electrons
in order to have a full valence shell (a
stable_________ or a _______ ________
configuration).
Metals and nonmetals have large differences in
electronegativity.
– Electronegativity is the ability of an element’s atoms
to …
So, metals and nonmetals react to form binary
ionic compounds.
– Recall, an ionic bond is the attraction between…
Ionic bonds are formed by the
attraction of oppositely charged ions.
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But sometimes two atoms that both need
to gain valence electrons to become stable
have similar attractions for electrons (i.e.,
they have similar electronegativites).
– This usually occurs with nonmetals.
How do atoms that do not give up
electrons bond with each other?
….they share!
– Examples hydrogen and fluorine
Molecules
Covalent bond
—the chemical bond that results from the
sharing of pairs of valence electrons
Molecule
—forms when two or more atoms bond
covalently
(Recall, ionic compounds do not form
“molecules,” but formula units. )
Diatomic molecules
A diatomic molecule is two atoms of the
same element covalently bonded.
– Diatomic molecules form because they are
more stable than the individual atoms.
Seven elements naturally exist as diatomic
molecules.
These elements form the shape of a 7 on
the periodic table.
– H2 and N2, O2, F2, Cl2, Br2, I2
Covalent Bonds
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Nitrogen Fixing Bacteria
Nitrogen is essential for all life on
this planet, but most of it is in the
air, making up about 78% of the
earth's atmosphere.
Bacteria are the only organisms
capable of taking gaseous
nitrogen and breaking the triple
covalent bond to combine it with
hydrogen to make ammonia.
So nitrogen-fixing bacteria are an
essential part of all ecosystems.
Mostly they are free-living soil
organisms, but some plants have
developed an association with
bacteria which infect their roots
and , in return for sugars from the
plant, fix nitrogen which can be
used by the plant for growth.
From http://www.hcs.ohio-state.edu/HCS300/bact.htm
Nitrogen Fixing Bacteria
Nitrogen fixation usually
refers to the biological
process by which nitrogen
(N2) in the atmosphere is
converted into ammonia.[1]
This process is essential
for life because fixed
nitrogen is required to
biosynthesize the basic
building blocks of life, e.g.
nucleotides for DNA and
amino acids for proteins.
Formally, nitrogen fixation
also refers to other
abiological conversions of
nitrogen, such as its
conversion to nitrogen
dioxide.
From Wikipedia
Schematic representation of the nitrogen cycle.
The most important belong
to the genus Rhizobium,
which infects the roots of
both trees and herbaceous
plants in the bean family
(Fabaceae or
Leguminosae).
The bacteria live in
nodules on the plant root.
The reduction of nitrogen
to ammonia can only occur
in the absence of oxygen.
The sheath of plant cells
around the bacteroids
keeps oxygen out.
VSEPR Theory
Valence Shell Electron Pair
Repulsion
VSEPR MODEL and Molecular
Shapes
VSEPR stands for…
define (p 242):
Shared pairs of electrons…
Lone pairs of electrons…
Book page 259….
Journal page 31
VSEPR Model
The Valence Shell Electron Pair Repulsion model
predicts the shapes of molecules and ions by
assuming that the valence shell electron pairs are
arranged as far from one another as possible to
minimize the repulsion between them.
Chemistry: The Molecular Science, 3rd Ed. by Moore, Stanitski, and Jurs
Water Chemistry
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Water Chemistry
All living organisms are dependent on
water. All living things are 70–90% water.
The structure of water is the basis for its
unique properties.
The most important property of water is
the ability to form hydrogen bonds.
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molecules
Molecule of water
Water Chemistry
Within a water molecule, the bonds between
oxygen and hydrogen are highly polar.
Partial electrical charges develop:
- oxygen end is partially negative
- hydrogen end is partially positive
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Page 39
Structure of the water
molecule.
Page 40
Hydrogen bond between two
water molecules.
Water Chemistry
Hydrogen bonds are weak attractions between
the partially negative oxygen of one water
molecule and the partially positive hydrogen of a
different water molecule.
Hydrogen bonds can form between water
molecules or between water and another
charged molecule.
Water Chemistry
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Water Chemistry
The polarity of water causes it to be
cohesive and adhesive.
Polarity unequal charge distribution in a molecule
resulting in a – region and a + region
Cohesion (surface tension): water
molecules stick to other water molecules
by hydrogen bonding
adhesion: water molecules stick to other
polar molecules by hydrogen bonding
Water Chemistry
cohesion
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Water Chemistry
adhesion
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Properties of Water
1. Water is a POLAR MOLECULE.
--see how a microwave oven works using
water’s polarity, book page 270.
2. Water has a high specific heat.
- A large amount of energy is required to
change the temperature of water.
3. Water has a high heat of vaporization.
- The evaporation of water from a surface
causes cooling of that surface.
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Ice
Polar water molecules form six-sided
crystals when freezing.
H-bonding in ice
Properties of Water
4. Solid water is less dense than liquid
water.
- Bodies of water freeze from the top
down.
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Properties of Water
5. Water is a good
solvent.
- Water dissolves polar
molecules and ions.
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Properties of Water
6. Water organizes nonpolar molecules.
- hydrophilic: “water-loving”
-hydrophobic: “water-fearing”
- Water causes hydrophobic molecules to
aggregate or assume specific shapes.
7. Water can form ions.
H2O  OH-1
+
hydroxide ion
H+1
hydrogen ion
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Ionization; happens spontaneously
Unique Properties of Water
(H2O)
Water has the highest specific heat capacity of all liquids (1 cal/g/deg C)
Solid water (ice) is less dense than liquid water.
Water is one of the few inorganic substance that is a liquid at room temperature and 1 atmosphere
Water has the highest surface tension of all liquids except mercury.
Water demonstrates strong capillary action.
Water has the greatest thermal conductivity except for mercury
Water is the most universal solvent
Water has a high heat of vaporization and heat of fusion.
Water is the only molecule with vibrational overtones in the visible region (This is why large bodies of water are
blue)
Water has a pH of 7 and can act as an aci or a base.
Water exists as a liquid over an important range of temperature from 0 - 100° Celsius. This range allows water to
remain as a liquid in most places on the Earth.
Water is the only substance on Earth that exists as a solid, liquid, and a gas.
Unique Properties of Water
Solid water (ice) is less dense than liquid water.
Water has the highest surface tension of all liquids
except mercury.
– It beads up
Water is the most universal solvent
– it dissolves both polar and ionic compounds.
Water has a pH of 7 and can act as an acid or a base (it
is neutral).
Water is the only substance on Earth that exists as a
solid, liquid, and a gas.
Structure of Ice
Observe the orientation of the
Hydrogen Bonds
HB-ice