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The Chemistry of LifeChapter 2
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The Chemistry of Life
• Matter- anything that takes up space and
has mass- everything around us
• Element- Substance that cannot be
broken down to other substances by
chemical reactions.
• 92 naturally occurring
• Compound- Substance of two or more
different elements combined in a fixed
ratio.
-IE- NaCl or Steel
• Essential Elements
Carbon, oxygen, nitrogen, hydrogen
compose 96% of living matter.
• Phosphorus, sulfur, potassium, calcium
and trace elements compose the
remaining 4%.
• Trace elements still necessary for life.
• Proton- positive, circa 1 Dalton *atomic
mass unit (amu), located in nucleus
• Neutron- neutral, circa 1 Dalton,
located in nucleus
• Electron- negative, circa 1/2000 of
a Dalton, orbits the nucleus
Subatomic particles-
• Atomic number: number of protons
– if a neutral atom, then proton # = electron #
• Mass number (atomic mass):
Protons + neutrons.
Mass number will be greater (or equal to, in
the case of hydrogen) than atomic number.
❖David Anguelov
❖Rohan Benda
❖Mia Crossen
❖Belen Hernandez
❖Emily Lindley
❖Noah Rivera
Test Average: 81%
GREAT WORK! (*without extra credit question!)
• Isotope- Some elements have a differing number of neutrons. SAME chemical properties.
IE- Carbon. Exists in three different isotopes.
C-12 (99% in nature)
C-13 (almost 1%)
C-14 (miniscule amount found in nature).
C-14 is a radioisotope- nucleus decays spontaneously causing radiation.
Isotopes
Used as a “tracer” (substance used to track the flow of C in an organism)*helps determine ages of fossils
Iodine-131
• Radioactive Isotope
used to detect and
treat
hyperthyroidism and
some thyroid
cancers
• Half life to 8 days
• Energy levels of electrons- Energy is
defined as the capacity to cause change.
• Electron energy level closest to nucleus is
at lowest energy level.
• Electron energy levels increase in energy
as we move away from the nucleus.
* Valence e- important for atom interactions & bonding
• Valence electrons are the electrons in the
outermost shell.
– Non-reactive if this shell is full (noble
gases) *INERT; “happy”
• Orbitals:
– First shell can hold 2 electrons (1s)
– Second shell can hold 8 electrons (2s and
three 2p’s). Cannot have more than 2
electrons per orbital.Animations of valence
electrons
Covalent Bonding
• Covalent Bonding- sharing of valence electrons. Some of the strongest bonds found in living matter.
• H-H is a single covalent bond, each H is sharing its one electron (structural formula). – H2 (molecular formula)
• Bonding capacity is based on how many electrons are needed in valence shell, and an atoms “valence” = the number of unpaired electrons in the outermost shell.
Electronegativity
• Electronegativity- attraction of a
particular atom to the electrons shared in
a covalent bond.
• More electronegative atoms pull harder
on the electrons.
– *more greedy and becomes an “unequal
share”
Polar and non-polar COVALENT bonds
Non-polar covalent bonds
• When electrons are shared equally
between two atoms of the same type
(IE- Cl-Cl) then it is a non-polar covalent
bond.
*No pull!
Polar covalent bond
• When the electrons are NOT shared
equally it is considered a polar covalent
bond.
Electronegativity and oxygen
• Oxygen is the *2nd
most electronegative of
all 92 elements
(commonly found in an
organism).
• Where ever the
electrons are being
pulled closest to will
have a slight negative
charge (notated as δ-).
2nd Quarter!
Q.Q. 10/22/18The atomic number of Sulfur is 16. Sulfur combines with
hydrogen by covalent bonding to form a compound,
hydrogen sulfide. Based on the # of valence e- in a sulfur
atom, predict the molecular formula of the compound.
a) HS
b) HS2
c) H2S
d) H3S2
e) H4S
2nd Quarter!
Q.Q. 10/22/18The atomic number of Sulfur is 16. Sulfur combines with
hydrogen by covalent bonding to form a compound,
hydrogen sulfide. Based on the # of valence e- in a sulfur
atom, predict the molecular formula of the compound.
a) HS
b) HS2
c) H2S
d) H3S2
e) H4S
Ionic Bonding
• Ionic bonding- The two atoms are so
unequal in their attraction to the valence
electrons that the stronger of the two strips
the electron away from the other atom.
*completely removes; no sharing!
IE- Sodium (11 electrons, single electron in
valence) and chlorine (17 electrons, 7 electrons
in valence). Chlorine strips the single electron
away from the sodium, fulfilling the octet in the
valence shells of both.
Ionic Bonding
• Because of this donation, the sodium is now
positive (has 11 protons, 10 electron) and is
called a cation.
• Chlorine is now negative (17 protons and 18
electrons) and is called an anion.
• Cations and anions attract forming this ionic
bond. These bonds form salts.
Video of
formation
reaction
Hydrogen Bonds
• Weak bonds- Some of the most important
bonds in living matter. Reversible
– Hydrogen bonds- H atom that is covalently
bonded to an electronegative atom is
attracted to another electronegative atom
(usually O or N in living matter).
Van der Waals forces
• Weak bonds
• Van der Waals forces- “hot spots” of
positive and negative charges because of
random electron movement (weak bond,
but strong enough to hold a gecko on a
wall) – TED Ed- How geckos defy gravity
Molecular shape and function
• When two matching atoms bond it will be a
linear molecule.
• Larger molecules are very complicated
and their shape is CRUCIAL in
recognition in biological systems.
Chemical reactions
• Chemical reactions- Making and breaking
bonds.
• Reactants Product(s)
• We cannot create or destroy matter, only
rearrange it.
• Some reactions are reversible, some are not (said to have gone “to completion”).
• If we increase the concentration of reactants then we will speed up the reaction.
• Chemical equilibrium-Forward and reverse reactions balance each other out and there is no net effect on the concentrations of the reactants or products.