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Bonding, Carbon and Water
Mini Lecture 2.2
AP Biology
• Atoms with unfilled outer shells tend to
undergo chemical reactions to fill their outer
shells.
• They can attain stability by sharing electrons
with other atoms (covalent bond) or by losing
or gaining electrons (ionic bond)
• The atoms are then bonded together into
molecules.
• Octet rule—atoms with at least two electron
shells form stable molecules so they have
eight electrons in their outermost shells.
Ionic bonds
• Ions are charged particle that form when
an atom gains or loses one or more
electrons.
•
Cations—positively charged ions
•
Anions—negatively charged ions
• Ionic bonds result from the electrical
attraction between ions with opposite
charges.
•
The resulting molecules are called salts.
Covalent bonds
• Covalent bonds form when two atoms
share pairs of electrons.
• The atoms attain stability by having full
outer shells.
• Each atom contributes one member of the
electron pair.
• Carbon atoms have four electrons in the
outer shell—they can form covalent bonds
with four other atoms.
Strength and stability—covalent bonds are
very strong; it takes a lot of energy to break
them.
• Multiple bonds
• Single—sharing 1 pair of electronsC H
•
C C
Double—sharing 2 pairs of electrons
•
N N
Triple—sharing 3 pairs of electrons
Degree of sharing electrons is not always
equal.
• Electronegativity—the attractive force that
an atomic nucleus exerts on electrons
• It depends on the number of protons and
the distance between the nucleus and
electrons.
• If two atoms have similar
electronegativities, they share electrons
equally, in what is called a nonpolar
covalent bond.
• If atoms have different electronegativities,
electrons tend to be near the most
attractive atom, in what is called a polar
covalent bond
Polar Covalent Bonds
• Electronegative O pulls efrom H
• This causes a partial (+)
charge on the H, and a
partial (-) charge on the O
• Partial charges are
indicated by lower case
deltas (d)
• The bonds between O and
H are polar covalent bonds
Biology, Sixth Edition
Chapter 2, Atoms and
Molecules
d+
d-
d+
Water Forms
Hydrogen Bonds
• Partial charges
interact
• Hs attracted to
Os
• Causes water to
self-associate
Biology, Sixth Edition
Chapter 2, Atoms and
Molecules
Hydrogen Bonding
• Gaseous water
molecules interact very
little
• Liquid water molecules
are hydrogen bonded,
but can slip past each
other
• As water freezes, it
forms a crystalline
lattice because H
bonding lasts longer
Biology, Sixth Edition
Chapter 2, Atoms and
Molecules
Water is “Sticky”
• Water is sticky because of H bonding
• Cohesive – sticks to itself
• Adhesive – sticks to other things
– Meniscus
Biology, Sixth Edition
Chapter 2, Atoms and
Molecules
Water has High Surface Tension
• Water sticks to itself strongly and so has
high surface tension
– Forms meniscus
– Forms droplets
– Small animals can ‘skate’ on surface
Biology, Sixth Edition
Chapter 2, Atoms and
Molecules
Other water properties
• High specific heat
• High heat of vaporization
• Great solvent
• Carbon:
Carbon
• Is the single most abundant element of Life
• Is neither strongly electronegative nor positive
• Can share 4 electrons and form 4 covalent bonds with 4 other atoms
(single, double or triple bonds)
• Interacts with many other atoms
• Makes a great variety of molecules – because it can form straight or
branched chains or rings
• The diversity of carbon-carbon interactions provides for
the diversity of biomolecules: lipid, carbohydrate,
protein, nucleic acid
Biology, Sixth Edition
Chapter 3, Chemistry of Life:
Carbon Double Bonds
• 2 double bonds connect O to C on either side, and the
molecule is linear.
• As a result, oxygen atoms pull on electrons in a linear
manner and so carbon dioxide is nonpolar.
Biology, Sixth Edition
Chapter 3, Chemistry of Life:
Covalent Carbon-Carbon Bonds
• Carbon may form…
• single bonds
H
H
C
C
H
H
C
C
H
H
H
H
C
C
– ethane
• double bonds
– ethene
H
• triple bonds
H
– ethyne
H
H
H
C
C
H
H
Biology, Sixth Edition
Chapter 3, Chemistry of Life:
H H
H
H
C
C
H H
C
C H
H
H
All strict hydrocarbons
- those with
Hydrocarbons:
C
&
H
only C and H - are hydrophobic &
don’t mix with H 2O
Biology, Sixth Edition
Chapter 3, Chemistry of Life:
• Macromolecules
• Most biological molecules are polymers
(poly, “many”; mer, “unit”), made by
covalent bonding of smaller molecules
called monomers.
4 MAIN Macromolecules
• Proteins: Formed from different combinations
of 20 amino acids
• Carbohydrates—formed by linking similar
sugar monomers (monosaccharides) to form
polysaccharides
• Nucleic acids—formed from four kinds of
nucleotide monomers
• Lipids—noncovalent forces maintain the
interactions between the fatty acid monomers
Polymers are formed and broken apart in
reactions involving water.
• Condensation—removal of water puts
monomers together (dehydration synthesis)
• Hydrolysis—addition of water breaks a
polymer into monomers
PDQ 2.2
1. Ionic vs. Covalent
Ionic
• 1 atom donates to another
atom in order to fill their
outer shells
• Metal donates to the
nonmetal
• Bond occurs from attraction
of cation (+) to anion (-)
Covalent
• Both atoms share electrons
in order to fill their outer
shells
• Occurs between 2
nonmetals
• Bond can be polar (shared
unequally)or nonpolar
(shared equally)
2. Electronegativity
• Attractive force than an atomic nucleus exerts
on electrons in a covalent bond
• Causes covalent bonds to not be shared
equally
• Causes partial charges on atoms
3. Nonpolar Covalent vs. Polar
Covalent
Nonpolar Covalent
• Bond in which electrons are
shared equally
• Occurs when 2 atoms are
close to each other in
electronegativity
Polar Covalent
• Bond in which electrons are
not shared equally
• Occurs when 2 atoms are
NOT close to each other in
electronegativity
• Causes partial charges on
atoms
4. Hydrogen bond and differences
• Occurs between a partially positive charged
atom and a partially negatively charged atom
• It differs from a covalent bond because
electrons are not being shared
• It differs from an ionic bond because the
charges are partial
• It is weaker than both a covalent and an ionic
bond
5. Hydrophilic vs. Hydrophobic
Hydrophilic
• Water loving
• Polar
• Attracted to water
• Dissolves in water
• Usually caused by polarity
Hydrophobic
• Water fearing
• Nonpolar
• Attracted to nonpolar
substances like oil
• Does not dissolve in water
6. Van Der Waals
Compare
• Chemical bond
Contrast
• Very weak compared to all
other chemical bonds
• Interaction of electrons of
nonpolar substances only 
no polar substances are
involved
7. Rank bonds from least to
greatest energy
•
•
•
•
•
Van Der Waals
Hydrophobic interactions
Hydrogen Bond
Ionic Bond
Covalent Bond
8. Why is water polar?
• Because the oxygen and hydrogen do NOT
share their electrons equally
• Oxygen wants the electron more because it is
MORE electronegative
• Therefore Oxygen gets more of a negative
charge and hydrogen gets more of a positive
charge
• This means it is polar and unbalanced.
9. Water bonding – showing
hydrogen bond
10. Water properties
Property
Definition
Special
Example
High heat capacity
Water is slow to
change
temperature
Many hydrogen
bonds
Takes a long time to
boil water
High heat of
vaporization
Lots of energy is
needed to go from
liquid to gas
Hydrogen bonds
have to be broken
Sweating
Evaporative Cooling When water
evaporates it cools
Breaking hydrogen
bonds
When you sweat,
you cool down
Cohesion
Attraction to each
other
Polarity in hydrogen Puddles
bonds
Adhesion
Attraction to other
molecules
Polarity in hydrogen capillarity
bonds
Surface Tension
Attractive
intermolecular
forces at the
surface of a liquid
Polarity in hydrogen Insects walking on
bonds
water
11. Inorganic vs. Organic
Inorganic
• No carbon AND hydrogen
• smaller
Organic
• Has carbon AND hydrogen
• LARGE
12. Carbon 
• Has 4 Valence electrons
• Can bond with 4 other atoms
• Possibilities are endless of what carbon can
make!
13. Functional Groups
Functional
Group
Drawing
Name of
Compounds
Example
Property
Hydroxyl
Alcohols
Ethanol
Polar.
Hydrophilic
Carbonyl 1
Aldehydes
Acetalaldehyde
Very reactive
Carbonyl 2
Ketones
Acetone
Important in
Carbohydrates
Carboxyl
Carboxylic
Acids
Acetate
Acidic. Ionizes
in living tissues
Amino
Amines
Methylamine
Basic. Accepts
H+’s in living
tissues
Sulfhydryl
Thiols
Mercaptoethanol
Can form
disulfide bridges
Phosphate
Organic
Phosphates
3-Phosphoglycerate Negative
charged.
14. Bonding interactions for each
functional group
Functional Group
Interaction
Hydroxyl
Condensation
Carbonyl 1 – Aldehyde
Energy Releasing, Condensation
Carbonyl 2 - Ketone
Energy reactions
Carboxyl
Condensation – gives up OH; Energy
releasing
Amino
Condensation – gives up H
Sulfhydryl
Forms disulfide brides in proteins
Phosphate
Condensation – gives up OH, hydrolysis
when bonded to another phosphate
15. Macromolecules
1.
2.
3.
4.
Carbohydrates
Lipids
Proteins
Nucleic Acids
16. Making Macromolecules
• Condensation or Dehydration Synthesis
16. Breaking Macromolecules
• Hydrolysis