Chapter 2
Chemical Foundations
for Cells
Chemical Benefits and Costs
•Chemical pollutants damage ecosystems
•Understanding of chemistry
provides fertilizers, medicines,
etc.
Elements
• Fundamental forms of _________
• Can’t be broken apart by normal
means
• ___ occur naturally on Earth
Most Common Elements in Living Organisms
•________
•________
•___________
•__________
What Are Atoms?
• Smallest particles that retain properties of an element
• Made up of subatomic particles:
– ______ (+)
– __________(-)
electron
– _________ (no charge)
proton
neutron
Atomic Number
= Number of ___________
Carbon= 6 protons
HELIUM
Mass Number
= # of _______ + # of _______
Isotopes
= Atoms of an element with different numbers of
______(different mass numbers)
•Carbon 12 has 6 protons, 6 neutrons
•Carbon 14 has 6 _____, 8 ________
Radioisotopes
•Have an _____ nucleus that emits energy and particles
•Decay occurs at a _____ rate
Radiation therapyusing radioisotopes to destroy _________cells
normal thyroid
Thyroid
Scan
enlarged
cancerous
What Determines Whether
Atoms Will Interact?
Answer- The _____ and ________ of
their electrons
Electrons
• Carry a ______ charge
• Repel one another
• Are attracted to _______ in the
nucleus
• Move in orbitals (shells)
1st
shell- ___electrons max
2nd, 3rd and 4th shells- ___electrons max
Only _______ electrons matter!
CALCIUM
20p+ , 20e-
Electron Vacancies make atoms reactive
Hydrogen, carbon, oxygen, and nitrogen all have
vacancies in their ____ shells- hence are ______
HYDROGEN
1p+ , 1e-
CARBON
6p+ , 6e-
NITROGEN
7p+ , 7e-
•A bond is union between electron structures of atoms
What holds molecules together?
Three major bonds
•_________ Bonds= share electrons
•________ Bonds= swipe or gain electrons
•__________ Bonds= weak, opposite charge
attraction
a._______
b. __________
c. ____________
Strong
Weak
_____________ Atoms share a pair or pairs of
electrons to fill outermost shell
•Single covalent bond
•Double covalent bond
•Triple covalent bond
_________ Covalent Bonds
• Atoms share electrons _______
• Nuclei of atoms have same number of
______
• Example: Hydrogen gas (H-H)
________Covalent Bonds
• ______ # of protons
• Electrons near nucleus with most protons
• Water - Electrons more attracted to O nucleus
than to H nuclei
• __________ –between two atoms are so unequal
in their attraction for valence electrons that one
atom strips an electron completely from the other.
– Example- sodium (one valence electron) in its third
shell transfers this electron to chlorine with 7 valence
electrons in its third shell.
– Now, sodium has a full valence shell (the second) and
chlorine has a full valence shell (the third).
These are now
called ____
Na+ is a _______
Fig. 2.14
Cl- is an _______
Cations and anions are attracted - form __________
• ___________ - a hydrogen atom that is already
________________ bonded to a strongly
electronegative atom is attracted to another strongly
electronegative atom.
• Example- ammonia molecules and water
molecules link together with weak hydrogen
bonds.
– Hydrogen atoms - partial ______ charges
– Nitrogen atom - partial ________ charge.
• Thus- ammonia forms hydrogen bonds with
water
Fig. 2.16
The magic of water
The polarity of water molecules results
from _____________ bonding
• Water molecule- two
hydrogen atoms
form ______
_______ bonds with
an oxygen atom.
– Partial negative
charge
– Partial positive
charge
_______- because each share one electron
_____- because O is more electronegative than H
_______- because they each share electrons
• Water has unusual properties because of
attractions between _____ molecules.
– The slightly negative regions interact with
slightly positive regions of nearby molecules,
forming a hydrogen bond.
– Each water molecule
can form hydrogen
bonds with up to
____ neighbors.
Fig. 3.1
The magic of water
a.cohesion
Water adheres to itself- called _______
• How? By _______ bonds
• Water cohesion is key role in the ____
________in plants.
– Water that evaporates from a leaf is replaced
by water from vessels in the leaf.
• ________, clinging
of one substance to
another, contributes
too
The magic of water
b.Surface tension
• _____________, a measure of the force
necessary to stretch or break the surface
of a liquid, is related to cohesion.
– Water has h igh _______________
– Why? __________ bonds resist breaking the
surface.
– Water behaves as if
covered by an invisible
______.
The magic of water
c.Temperature stabilization
Water moderates temperatures on Earth
• Water _______ air temperatures by ___________ heat from
warmer air and releasing heat to cooler air.
• Water can absorb or release relatively _________ of heat
with only a slight change in its own temperature.
• Water resists changes in temperature
– Why? ________________.
– Heat must be absorbed to break __________________
and is released when hydrogen bonds form.
The magic of water
d. evaporative cooling
• As a liquid evaporates, the surface of the liquid that
remains behind cools - ___________________.
– The most energetic molecules evaporate, leaving the
lower kinetic energy molecules behind.
• Evaporative cooling moderates
___________________ in lakes and ponds and
prevents terrestrial organisms from overheating.
– Evaporation of water from the leaves of plants
or the skin of humans removes excess heat.
The magic of water
e. Prevent lake freezing
• Water (unlike most liquids) is less dense as a solid than
as a liquid.
– At 0oC-water becomes a
______________________ with each molecule
bonded to the maximum of ______ partners.
– Ice is about ___________ dense than water at
4oC, thus ice _____.
If ice sank, eventually all ponds, lakes, and even the ocean would
freeze solid.
The magic of water
f. Powerful solvent
Water dissolves almost anything polar or ionic
• ________- A completely _______________
mixture of substances.
• ______ = dissolving agent
• _______ = agent being dissolved.
– Example-water is a solvent and sugar the solute.
Hydrophobic vs. hydrophilic
• Affinity for water = _________.
– Substances with _______________ bonds.
• no affinity for water = _______________.
– substances with ___________________
covalent bonds.
• Example-Oils, such as vegetable oil, are non-polar
• Hydrophobic molecules are major ingredients of ___
_________________.
• How do we measure acidity?
– Answer: In ____________.
• A water molecule dissociates into a hydrogen ion
and a hydroxide ion:
• H2O <=> H+ + OH• At equilibrium the concentration of H+ or OH- is 10-7M
(25°C) .
• Hydrogen and hydroxide ions are very reactive, and
thus drastically affect the proteins and other
molecules of a cell.
• How do we measure acidity?
– Answer: In _______.
The pH Scale
• Measures ___ concentration of fluid
• Change of 1 on scale means ____
change in ____ concentration
Highest H+
Lowest H+
0---------------------7-------------------14
______
Neutral
_____
Examples of pH
• Pure water is neutral with pH of ____
• Acidic- pH= < 7.0
– Stomach acid: pH ____________
– Lemon juice: pH ____
• Basic- pH= > 7.0
– Seawater: pH 7.8 - 8.3
– Baking soda: pH _____
• Weak acids- Reluctant H+ donors
– __________ acid (H2CO3)
• Strong acids- Completely give up H+ when dissolved
– HCl (hydrochloric acid)
Carbonic Acid-Bicarbonate
Buffer System
• When blood pH rises, carbonic acid
dissociates to form ____________ and __
H2C03 -----> HC03- + H+
• When blood pH drops, bicarbonate binds
H+ to form ________ acid
HC03- + H+ -----> H2C03
• ______________ (a product of the formation of carbonic
acid from carbon dioxide and water) occurs when rain,
snow, or fog has a pH that is more acidic than 5.6.
•caused primarily by _____________ and ______
______ from burning of fossil fuels
Rain in the Adirondack
Mountains of upstate New
York averages a pH of ____
Great impact on eggs and
early developmental stages
of _________ organisms
This has done major
damage
to forests in Europe and
substantial damage of
forests in North America
Isotope?
Radioactive isotope
Reactivity of an atom?
What is a valence shell?
Is this reactive?
How
many
valence
electrons?