Transcript Chapter 2: The Chemical Basis of Life

Chapter 2: The Chemical Basis of
Life
The Nature of Matter
Matter is anything that takes
up space and has mass

Matter is composed of
elements which are
substances that cannot be
broken down any smaller by
normal chemical processes

CHNOPS are six important
elements for life:Carbon,
Hydrogen, Nitrogen, Oxygen,
Phosphorus, and Sulfur

Atomic Structure
Names are represented by
atomic symbols

Atomic mass is dependent
on the number of protons,
neutrons, and electrons

Protons are positive,
electrons are negative, and
neutrons are neutral

Protons and neutrons are in
the nucleus, electrons orbit
around the nucleus.

Atomic Structure Continued
Atomic mass usually
equals the sum of protons
and neutrons as electrons
have very little mass

Each proton and neutron
weighs one atomic mass
unit

The atomic number is
equal to number of protons

Periodic Table
olumns are groups
ows are Periods
Group 8 is the noble
ases
Isotopes
Atoms of the same
element that differ in
number of neutrons

Named by the atomic
symbol and atomic mass
(C14)

Can be unstable and omit
radioactive particles

Arrangement of Electrons in an
Atom
It is impossible to pinpoint an
electrons exact location as they
are moving very quickly

Electrons are arranged in
electron shells that contain set
numbers of electrons

Arrangement of Atoms in an
Electron Continued
The first shell can hold two
electrons

After the first shell, an atom is
most stable when its outer shell
contains eight electrons

The number of valence (outer
shell) electrons an element has
determines its reactivity

Types of Chemical Bonds
A group of atoms is a
molecule

Two or more atoms of
different elements
joining forms a
compound

Ionic Bonding
Atoms are held by
attracting opposite
charges after an electron
transfers

Salts are ionic bonds

Ionic bonds can
dissociate or break apart
in many biological
environments

Covalent Bonds
Formed when atoms share
one or more electrons

Can form complex three
dimensional shapes

In a structural formula a
line illustrates a bond

Hydrogen, Oxygen, and
Nitrogen molecules are all
bonded covalently

Chemical Reactions
Displayed in an
equation

Reactants are on the
left, products are on the
right

Equations must be
balanced with the same
number of atoms of
each element on both
sides

Water's Importance to Life
The Structure of Water
Atoms differ in electronegativity (how
equally they share electrons)

Polarity can result where one side of a
molecule is slightly positive and the
other side is slightly negative

Water forms a V shape with Oxygen at
the point of the V which is slightly
negative, the hydrogens are slightly
positive

Water molecules can form hydrogen
bonds with each other making them
cohesive

Properties of Water
Water is a Solvent



Because of it
polarity, water
dissolves many
substances
Substances that easily
dissolve in water are
hydrophilic
Substances that do not
easily dissolve in water are
hydrophobic
Water Molecules are Cohesive and
Adhesive



Cohesion is the
ability of water
molecule to stick
together through
hydrogen bonding
Adhesion is the
ability of water to
stick to polar
surfaces
Cohesion and
adhesion are
essential to water
transport in plants
Water Has High Surface Tension

Cohesion causes
surface water to
stick together
which is important
to many aquatic
organisms
Water Has a High Heat Capacity

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Hydrogen bonds
allow water to
absorb a lot of heat
without changing
temperatures
Water also has a
high heat of
vaportization
Mediterranean
climates are created
when water absorbs
heat through the
summer and slowly
releases it during
Water is Less Dense than Ice

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Water expands as it
freezes so ice is
less dense than
liquid water so ice
floats on water
This allows aquatic
organisms to survive
winter
Acids and Bases

When water
dissociates it
releases hydrogen
and hydroxide ions
Acidic Solutions

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Release a high
concentration of
hydrogen ions
Often taste sour
Basic Solutions

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Have a high
concentration of
hydroxide ions
Have a bitter taste
and feel slippery
pH and pH scale


The pH scale is a
mathematical way of
representing
Hydrogen ion
concentration
It is a logarithmic
scale so a pH of 2
has ten times the
concentration of a pH
of 3
Buffers and pH

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In most organisms pH
must be kept in a
narrow range
Buffers are chemicals
that keeps pH within
normal limits