Transcript Elements of Life, Basic Chemistry, pH

Chapter 2 Opening Question
Why is the search for water important in
the search for life?
What are the six elements that living things are primarily
composed of?
• Carbon – C
• Oxygen – O
• Nitrogen – N
• Hydrogen – H
• Phosphorous – P
• Sulfur - S
Carbon
• Role: Major Structural atom in all organic
molecules
• Abiotic Source: The atmosphere (CO2)
• Biotic Processes: Photosynthesis and
Cellular Respiration and Decomposition
Oxygen
• Role: Major component of all organic
molecules; aerobic respiration
• Abiotic Source: The atmosphere (O2)
• Biotic Processes: Used in cellular
respiration. Released in photosynthesis
Nitrogen
• Role: Major component of proteins and nucleic
acids (DNA, RNA)
• Abiotic Source: Atmosphere (N2)
• Biotic Processes: bacteria convert N2 in air into
usable form for plants; Released to environment by
decomposition
Phosphorous
• Role: Major component of nucleic acids and
phospholipids (cell membrane); also used for energy
storage and release (ATP)
•
Abiotic Source: Rocks (lithosphere); Released in
weathering
•
Biotic Processes: Absorbed by plants in soil; Released
by decomposition
Sulfur
• Role: Major component of proteins (amino acid side
chain)
• Abiotic Source: Rocks - Lithosphere
• Biotic Processes: Absorbed by plants from the soil;
Released by decomposition
Hydrogen
• Role: Major component of all biological molecules;
Does not exist freely in nature
• Abiotic Source: Rocks – Hydrosphere (H2O
• Biotic Processes: Incorporated into food chains
along with water, Released through
decomposition/water release
What is the term used to describe other elements that are found in
much smaller amounts in organisms?
• TRACE ELEMENTS
• Potassium, Sodium, Iron, Zinc, Calcium,
Magnesium, Fluoride
• Essential for proper functioning of body
systems
Figure 2.2 The Periodic Table (Part 2)
He from periodic table here
Which identifies an element as being a particular
element?
Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry
• Atomic structure
• The element magnesium has an atomic number of 12
and a mass number of 24.
1. How many protons and neutrons are in the nucleus?
How many electrons are in this atom?
2. Is the magnesium atom likely to bond with other
atoms? Why or why not?
Figure 2.1 OCTET RULE
Chapter 2, Question 2
• Which of the atoms in the following figures can
form the most covalent bonds?
a. Li
b. C
c. N
d. O
Chapter 2, Question 3
• Lithium (metal) and fluorine (nonmetal) are most
likely to form which kind of bond?
a. Hydrogen
b. Ionic
c. Covalent
What is the difference between ionic and covalent bonding?
• Covalent bonding involves the sharing
of electrons – much stronger bond
• Ionic bonding involves the transfer of
electrons
Distinguish between nonpolar and polar covalent bonding.
• A polar covalent bond results when
electrons are unequally shared by
atoms because one atom has a
stronger attraction for them (ex: H2O,
HCl)
Figure 2.8 Water’s Covalent Bonds Are Polar
How is a hydrogen bond different from a colvalent or ionic bond?
• Hydrogen bonds: attractive force
BETWEEN molecules due to the
slightly + and -; weak force, but strong
in large numbers
Which inorganic molecule comprises over 70% of all organisms?
• WATER!!
Which two characteristics of water account for its special
properties?
 Polarity (H is + and O is -)
 Ability to form Hydrogen Bonds
Review: What is the structure of a biological
molecule important?
What are the special characteristics of water?
• High Heat Capacity
• Cohesion
• Surface Tension
• Adhesion
• Universal Solvent (“like dissolves
like”
• Less Dense in Solid Form than in
Water Video liquid form
• Temperature Buffer
Figure 2.14 Hydrogen Bonding and the Properties of Water
Concept 2.2 Atoms Interact and Form Molecules
Water molecules form multiple hydrogen bonds
with each other—this contributes to high heat
capacity.
Concept 2.2 Atoms Interact and Form Molecules
A lot of heat is required to raise the
temperature of water—the heat energy breaks
the hydrogen bonds.
In organisms, presence of water shields them
from fluctuations in environmental
temperature.
Concept 2.2 Atoms Interact and Form Molecules
Water has a high heat of vaporization—a lot
of heat is required to change water from liquid
to gaseous state.
Thus, evaporation has a cooling effect on the
environment.
Sweating cools the body—as sweat evaporates
from the skin, it transforms some of the
adjacent body heat.
2.4 What Makes Water So Important for Life?
• Cohesion: water molecules resist
coming apart from one another.
•
• Helps water move through plants
•
• Results in surface tension
Figure 2.15 Surface Tension
Surface Tension
Cohesion and Adhesion
What is the difference between a solvent and a solute?
• A solution is a substance (solute)
dissolved in a liquid (solvent).
• Many important biochemical reactions
occur in aqueous solutions.
Figure 2.10 Water Molecules Surround Ions
What is the difference between substances that are hydrophilic and hydrophobic?
2.2 How Do Atoms Bond to Form Molecules?
Polar molecules that form hydrogen
bonds with water are hydrophilic
(“water-loving”).
Nonpolar molecules such as
hydrocarbons (fatty acids, oils) that
that do not react with water, are
hydrophobic (“water-hating”).
SNAP – Symmetrical
Nonpolar, Asymmetrical Polar
Chapter 2, Question 4
• Which of the following characteristics does not
apply to water?
a. All three atoms in water readily form
hydrogen bonds with other molecules.
b. The covalent bonds in water are polarized.
c. The water molecule readily forms
hydrophobic interactions.
d. The water molecule is asymmetric.
Water Dissociates!
2.4 What Makes Water So Important for Life?
• A water molecule can be pulled apart
into a proton and a hydroxide ion by
other water molecules
• This happens approx. once for every
10,000,000 (10^7) water molecules
2.4 What Makes Water So Important for Life?
In pure water, the concentrations of H+
(H3O+) and OH- are each 10^-7 (one in
ten million)
The pH of pure water = _________
Physiological pH = ___________
Figure 2.14_3
Acidic
solution
Neutral
solution
Basic
solution
How do we identify substances as being acidic or basic?
• A compound that increases the [H+] of
a solution is an acid. This results in a
decrease in the [OH-] in solution.
• A compound that increases the [OH-] in
a solution is a base. This decreases
the [H+] in solution.
What is pH? How do you calculate the pH of a solution? MATH!!
• A measurement of the concentration of
H+ ions in a solution
• pH = - log [H+]
• IMPORTANT: [H+] x [OH-] = 10^-14
IMPORTANT: The concentrations of H+ and OHare INVERSELY proportional; As one ion
increases, the other decreases!!
Example:
• If a solution has a [H+] of 10^-4, what is
the pH of the solution?
• If a solution has a [OH-] of 10^-5, what
is the pH of the solution?
• If a solution has a pH of 10, what is the
[H+] of the solution?
pH Sale
pH is a logarithmic scale:
• Each whole number on the pH scale
represents a power of 10
• A solution with a pH of 5 has a [H+] that
is _____ times more acidic than a
solution with a pH of 7.
Chapter 2, Question 5
• Cola has a pH of 2 and black coffee has a pH of
5. How many times more concentrated are the
hydrogen ions (H+) in cola than in black coffee?
a. 10
b. 100
c. 20
d. 1000
Blood pH Question:
• Living organisms maintain constant
internal conditions (homeostasis).
• Buffers help maintain constant pH
because it can act as BOTH
Figure 2.17 Buffers Minimize Changes in pH