Atomic Structure

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Atomic Structure
2
Isotopes
3
Which atoms are likely to form a chemical bond
with other atoms, and why?
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Electron Shell Diagrams
Atoms tend to gain, lose or share electrons so as
to have 8 electrons in their outer most shell

• For H to be stable it needs
• For C to be stable it needs
• For N to be stable it needs
• For O to be stable it needs

1 more electron
4 more electrons
3 more electrons
2 more electrons
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• In order to fill those outer most shells (the
  valence shell) each atom will create a bond with
  another atom. The type of bond the atoms will
  create will depend on
• How many electrons they need to be stable.
• What type of atom they are bonding with.
• For example, it would be most beneficial for
  Carbon to __________ (share, gain, or lose)
  electrons.

SHARE
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IONIC BOND forming ions due to the loss or gain
of electrons.
Nas outer most shell is almost empty, Cls outer
most shell is is almost full Na transfer or
gives away one electron to Cl.
Atoms stay associated because opposite charges
attract IONIC BOND
Na gains a positive charge because it loses an
electron and goes from being a neutral atom to a
cation ( charged atom) Cl gains a negative
charge because it gains one additional electron
and becomes an anion (- charged atom).
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Ionic Bonds One Big Greedy Thief Dog!
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IONIC Bond - NaCl
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Now, lets talk about SHARING electrons. Or, a
COVALENT BOND!
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Covalent Bonds
Sharing electrons to fill the outer most shells
of both the hydrogen atoms and the oxygen atom
now everyone is happy.
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Covalent Bonds
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So, there is a covalent bond because the
electrons are being sharedbut what TYPE of
sharing is going on?!
(Equal Sharing!)
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Nonpolar Covalent Bonds Dogs of equal strength
(equal sharing!)
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Nonpolar Covalent bonds electrons are being
shared EQUALLY!!
Oxygen Atom
Oxygen Atom

Oxygen Molecule (O2)
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Nonpolar covalent bonding
Hydrogen (HH or H2), a nonpolar molecule
Oxygen (OO or O2), a nonpolar molecule
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Polar Covalent Bonds Willing to share, but
unevenly matched!
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Polar Covalent Bonding
Unequal sharing of electrons by the oxygen with
the hydrogens. The oxygen is winning at the
tug of war and therefore gaining a slight
negative charge.
(slightly negative)
(slightly positive)
(slightly positive)
Water (HOH or H2O), a polar molecule
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Polar Covalent Bonding, again..
Water is a polar molecule because oxygen is more
electronegative than hydrogen, and therefore
electrons are pulled closer to oxygen.
Polar Covalent bonds hold the O and Hs together
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Now, what happens when two or more POLAR
MOLECULES come in contact with each other?
Polar Covalent Bond
Polar Covalent Bond
Opposite charges will attract, and one water
molecule will cling to another water molecule,
and so on.
What bond does this create??
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HYDROGEN BONDS!
Because of the POLAR covalent bond between the O
and the H of H2O, the water molecule has
acquired slight charges on each end of the water
molecule.
Water Molecules
Water Molecules
The hydrogen bond forms between the slight
negative charge on the oxygen end of one water
molecule with the slight positive charge on the
hydrogen end of a different water molecule.


_
hydrogen bonds
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Take a look at the Hydrogen Bonding animation
that is posted on the website!
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Acids, Bases, and the pH Scale

• The ions that contribute to the pH of a solution
  are
• Hydrogen ions (H)
• Hydroxide ions (OH-)
• Diagram of water see next slide!

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water (H2O)
hydroxide ion (OH )
hydrogen ion (H)

• What should the balance of these ions be in
  PURE water?

In pure water, there should be equal
concentration of these ions!
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Definition of an acid is

• A substance that releases H ions therefore
  increasing the H concentration of a solution
• An example is hydrochloric acid (HCl)
• HCl H Cl-

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Definition of a base is

• A substance that reduces the H ion concentration
  of a solution (removes the H)
• And example is Sodium Hydroxide (NaOH)
• NaOH Na OH-
• How would this reduce the H in the solution?
  Think about what OH- plus H combine to form!

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The pH (potential hydrogen) scale is a
measurement of the concentration of ions in a
solution
Make note of some of these important examples!
The pH values of something acidic range from 0-6.9
Neutral is 7
Basic values range from 7.1-14
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How do cells and living organisms prevent the pH
from fluctuating?

• Buffers! Buffers are chemicals that minimize
  changes in the concentrations of hydrogen ions
  and hydroxide ions in a solution. They are able
  to accept and discard excess ions.
• These are crucial for living organisms as the
  internal pH of most cells is close to neutral.
  If that pH fluctuates, there can be problems with
  proper cell functioning!

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Now some questions..
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In water, hydrogen bonding occurs between the
hydrogen and

• An oxygen atom in the same water molecule
• A hydrogen atom in the same molecule
• An oxygen atom in a different molecule
• A hydrogen atom in a different molecule

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In water, hydrogen bonding occurs between the
hydrogen and

• An oxygen atom in the same water molecule
• A hydrogen atom in the same molecule
• An oxygen atom in a different molecule
• A hydrogen atom in a different molecule

Go back and look at the pictures of hydrogen
bonding!
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Which compound, LiF or F2, is mostly likely held
together by a covalent bond?(Li has a total of 3
e-s and F has a total of 9 e-s)

• LiF 3) Neither
• F2 4) Both

Draw out the electron shell diagrams!
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2) F2
F2
Sharing of the electrons to complete the valence
shell of each atom.
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Because water and oil do not mix, water is not
very effective at washing away oily dirt. The
ability of soap to mix with both water and oily
dirt allows soap to remove oily dirt. Which of
the following would be the best explanation for
this? Hint Consider whether water and oil are
polar!

• 1) Soap molecules have both positively and
  negatively charged regions. The positively
  charged regions are attracted to water and the
  negatively charged regions are attracted to oil.
• 2) Soap molecules have no charge. As a result,
  the soap molecules can bind to both water and
  oil.
• 3) Soap molecules have charged regions and
  uncharged regions. The charged regions interact
  with water while the uncharged regions interact
  with oil.
• 4) None of the above are logical explanations.

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Because water and oil do not mix, water is not
very effective at washing away oily dirt. The
ability of soap to mix with both water and oily
dirt allows soap to remove oily dirt. Which of
the following would be the best explanation for
this? Hint Consider whether water and oil are
polar!

• 1) Soap molecules have both positively and
  negatively charged regions. The positively
  charged regions are attracted to water and the
  negatively charged regions are attracted to oil.
• 2) Soap molecules have no charge. As a result,
  the soap molecules can bind to both water and
  oil.
• 3) Soap molecules have charged regions and
  uncharged regions. The charged regions interact
  with water while the uncharged regions interact
  with oil.
• 4) None of the above are logical explanations.

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Wine connoisseurs are concerned with the pH of
different wines as it will directly affect the
taste of the wine. Wines that get too acidic
taste sour and tart while wines that get to basic
taste flat and dull. The pH of most wines range
from 3.0-3.5. You measure the pH of a particular
wine that has yet to be bottled and it registers
a 6 on the pH scale. What should you do?

• Nothing, it is close to neutral and will taste
  fine.
• Add an acid to reduce the pH.
• Add a base to reduce the pH.
• Add a buffer to increase the pH.

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Wine connoisseurs are concerned with the pH of
different wines as it will directly affect the
taste of the wine. Wines that get too acidic
taste sour and tart while wines that get to basic
taste flat and dull. The pH of most wines range
from 3.0-3.5. You measure the pH of a particular
wine that has yet to be bottled and it registers
a 6 on the pH scale. What should you do?

• Nothing, it is close to neutral and will taste
  fine.
• Add an acid to reduce the pH.
• Add a base to reduce the pH.
• Add a buffer to increase the pH.