Transcript ChemicalBondingPowerpoint

KEY CONCEPTS
 Molecules form when atoms bond to each other. Chemical
bonds are based on electron sharing. The degree of
electron sharing varies from nonpolar covalent bonds, to
polar covalent bonds, to ionic bonds.
Chemical reactions tend to be spontaneous if they lead to lower
potential energy and higher entropy (more disorder). An input of
energy is required for nonspontaneous reactions to occur.
Water is a small, highly polar molecule. As a result, it is an
extremely efficient solvent and has a high capacity for
absorbing energy.
KEY CONCEPTS
 Water is a small, highly polar molecule. As a result, it is an
extremely efficient solvent and has a high capacity for
absorbing energy.
Each element has a characteristic number of protons. The
number of neutrons can vary; forms of an element with
different numbers of neutrons are called isotopes.
• Radioactive isotopes have unstable nuclei that emit
particles of radiation (energy) to form new daughter
isotopes. This is known as radioactive decay. The
energy may be released as beta particles (electrons),
gamma rays (pure energy), or alpha particles (helium
nuclei – positively charged and large).
Each radioactive isotope decays at a constant rate
quantified as its half-life
How Old Is the Earth?
• Meteorites formed 4.58 Ga, and the
Moon formed 4.51 Ga. Earth must be
about the same age, but no direct
radiometric dating is possible because
Earth was initially molten (Figure
2.4).
How Does Covalent Bonding
Hold Molecules Together?
• Atoms are most stable when each
orbital has two electrons. Atoms can
be joined by a covalent bond in
which each atom’s unpaired electrons
are shared by both nuclei to fill their
orbitals (Figure 2.7).
Bond Angles and the Shape
of Molecules
• Molecular shape depends on bond
angles, which in turn depend on the
orbitals in the bond (Figure 2.12).
 CHECK YOUR UNDERSTANDING
Covalent bonds are based on electron sharing,
while ionic bonds are based on electrical attraction
between ions with opposite charges. Covalent
bonds can be polar or nonpolar, depending on
whether the electronegativities of the two atoms
involved are the same or different…
 CHECK YOUR UNDERSTANDING
…You should be able to (1) draw the structural
formulas of methane (CH4) and ammonia (NH3)
and add dots to indicate the relative locations of
the covalently bonded electrons, and (2) draw the
electron shells around sodium ions (Na+) and
chloride ions (Cl-) and explain why table salt
(NaCl) exists.
What Is Energy?
• Energy is the ability to do work or supply heat.
Stored energy is called potential energy, and the
energy of movement is called kinetic energy or
thermal energy, which is measured as temperature.
The first law of thermodynamics states that energy
is conserved—it cannot be created or destroyed, but it
can be transferred or transformed
The Roles of Temperature and
Concentration in Chemical
Reactions
• High temperatures and high
concentrations cause more reactant
collisions and faster reaction rates.
2.4 The Composition of the Early
Atmosphere: Redox Reactions
and the Importance of Carbon
• Volcanic gases (mostly CO2, N2, and
H2O) probably dominated Earth’s
early atmosphere, but H2, NH3, and
CH4 were also present in sufficient
amounts to form H2CO and HCN.
What Is a Redox Reaction?
• In a reduction-oxidation (redox)
reaction, one molecule loses
electrons (is oxidized), another gains
electrons (is reduced), and an
electron donor is always paired with
an electron acceptor (Figure 2.20).
Functional Groups
• Carbon provides the structural
framework of organic compounds,
and functional groups containing H,
N, or O atoms bonded to C determine
their behavior (Table 2.1).
2.5 The Early Oceans and
the Properties of Water
• Life originated in and is based on
water because water is a great solvent
(substances dissolve easily in it).
• Water has several striking physical
properties: it expands as it changes from a
liquid to a solid, and it has an
extraordinarily large capacity for absorbing
heat.
Water is Denser as a Liquid than as a Solid
• Hydrogen bonds in ice connect water molecules in
an open crystal pattern. In liquid water, there are
fewer hydrogen bonds and the water molecules can
pack more tightly, making water denser than ice
(Figure 2.27).
Water has several striking physical properties: it expands
as it changes from a liquid to a solid, and it has an
extraordinarily large capacity for absorbing heat.
• Water’s temperature-buffering
capacity would have protected
dissolved HCN and CH2O from
energy sources in Earth's early
environment (such as asteroid
bombardment, volcanism, and
sunlight) that could have broken them
apart.
Acid-Base Reactions and pH
• In acid-base reactions, a proton
donor (acid) transfers a proton to a
proton acceptor (base).
Thalidomide effect – Fig. 3.29
1 optical isomer is a safe
tranquilizer – mirror image
inhibits blood vessel formation
– use as anticancer drug?
Thalidomide taken during narrow windows of limb
formation gave reduced or no arms or legs –
apparently by affecting blood vessel formation
How Do Amino Acids Link
to Form Proteins?
THE PEPTIDE BOND
CHECK YOUR UNDERSTANDING
Amino acids are small molecules with a carbon atom bonded
to a carboxyl group, an amino group, a hydrogen atom, and
a side chain called an R-group. Each amino acid has
distinctive chemical properties because each has a unique Rgroup. You should be able to draw the general form of an
amino acid.
When the carboxyl group of one amino acid reacts
with the amino group of another amino acid, a strong
covalent bond called a peptide bond forms. Polypeptides are
polymers made up of peptide-bonded amino acids. Small
polypeptides are called oligopeptides, and large polypeptides
are called proteins. You should be able to draw and label
two amino acids linked by a peptide bond.
3.3 What Do Proteins Look Like?
Quaternary Structure
QUATERNARY STRUCTURE
How Do Enzymes Work?
• Enzymes bring substrates together
in specific positions that facilitate
reactions and are very specific as to
which reactions they catalyze.
Escherichia coli – LPS/O antigens, OMPs, flagella,
peptidoglycan, inner membrane, DNA, ribosomes,
tRNA, various protein assemblies