Transcript Essentials of Biology Sylvia S. Mader

Essentials of Biology
Sylvia S. Mader
Chapter 2
Lecture Outline
Prepared by: Dr. Stephen Ebbs
Southern Illinois University Carbondale
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2.1 The Nature of Matter
• Matter refers to anything that takes up
space and has mass.
• Matter is composed of elements,
substances that cannot be broken down
into another substance.
– There are 92 natural elements.
– Living organisms are made primarily of six
elements.
2.1 The Nature of Matter (cont.)
Atomic Structure
• The atomic theory states that elements are
made of tiny particles called atoms.
• The name of an atom is represented by
the atomic symbol.
– Hydrogen = H
– Sodium = Na
– Chloride = Cl
Atomic Structure (cont.)
• Atoms are composed of three smaller
particles.
– Neutrons, which have no electrical charge.
– Protons, which have a positive charge.
– Electrons, which have a negative charge.
• Atoms have a mass number determined
by the weight of the neutrons and protons.
Atomic Structure (cont.)
Atomic Structure (cont.)
• All atoms of an element have the same
number of protons, the atomic number.
• The atomic number and mass number are
often included with the chemical symbol.
Mass number
Atomic number
12
6
C
Chemical symbol
The Periodic Table
• The elements are organized to form the
periodic table.
– The columns in the table are groups.
– The rows in the table are periods.
• Elements in groups have similar chemical
and physical characteristics.
The Periodic Table
Isotopes
• The atomic number indicates the number
of protons in an atom.
• The atomic mass is the sum of the number
of protons and neutrons.
• If an atom has the same number of
protons but a different number of neutrons
it is an isotope.
Isotopes (cont.)
• The nucleus of an isotope can be unstable
and may disintegrate, or decay.
• Decaying isotopes emit radiation.
• Radiation can be detected with
instruments such as a Geiger counter.
Uses of Radioactive Isotopes
• Radioactive isotopes can be used as
tracers to follow the movement of that
element.
• Radioactive isotopes can be used to
sterilize medical and dental instruments.
• Radioactive isotopes can also be used to
kill cancer cells.
Uses of Radioactive Isotopes
(cont.)
Uses of Radioactive Isotopes
(cont.)
Arrangements of Electrons in an
Atom
• Electrons encircle the nucleus of an atom
at discrete energy levels called electron
shells.
• In atoms with two or more shells, the outer
shell follows the octet rule (8 electrons)
• The electrons in the outer valence shell
determine the chemical reactivity of atoms.
Arrangements of Electrons in an
Atom (cont.)
Types of Chemical Bonds
• A group of atoms bonded to one another
form a molecule.
• If the molecule has more than one type of
element present it is a compound.
• Different types of bonds hold molecules
and compounds together.
Types of Chemical Bonds (cont.)
• Charged atoms, or ions, can form when
atoms lose or gain electrons.
• Positive and negative ions are attracted to
one another and bond together in ionic
bonds.
• A salt is a dry solid composed of atoms
connected by ionic bonds.
Types of Chemical Bonds (cont.)
Types of Chemical Bonds (cont.)
• A covalent bond results when two atoms
share electrons, thereby completing their
valence shells.
• When molecules contain covalent bonds,
the structure of the molecule can be drawn
with a formula or model.
Types of Chemical Bonds (cont.)
Chemical Reactions
• When molecules or compounds are
chemically changed it is called a chemical
reaction.
• Photosynthesis is an example of a
chemical reaction.
Chemical Reactions (cont.)
The chemical reaction for photosynthesis
6 CO2 + 6 H2O  C6H12O6 + 6 O2
carbon
dioxide
water
glucose
oxygen
• Molecules that participate in a reaction are
reactants.
• Molecules formed by a reaction are products.
2.2 Water’s Importance to Life
• Water is the single most important
molecule of earth.
• All organisms are 70-90% water.
• Water has unique properties that make it a
life-supporting substance.
The Structure of Water
• Atoms differ in their electronegativity, or their
affinity for electrons in a covalent bond.
• The unequal sharing of electrons in a
molecule such as water makes the molecule
polar.
• Polar water molecules are attracted to one
another and can form hydrogen bonds.
The Structure of Water (cont.)
Properties of Water
• Water is a solvent that can dissolve many
substances.
– Molecules that attract water are hydrophilic.
– Molecules that cannot attract water are
hydrophobic.
• Water dissolves polar nonionic
substances, ions, and some nonpolar
gases.
Properties of Water (cont.)
• Water shows cohesion and adhesion.
• When water molecules cling together with
hydrogen bonds it is called cohesion.
• When water molecules adhere to polar
surfaces it is called adhesion.
Properties of Water (cont.)
Properties of Water (cont.)
• Water also has a high surface tension.
• The stronger the force between molecules
in a liquid, the stronger the surface
tension.
Properties of Water (cont.)
Properties of Water (cont.)
• Water has a high heat capacity, protecting
organisms from temperature changes.
• Water has a high heat of vaporization.
• These properties of water keep
temperatures compatible with those of
living organisms.
Properties of Water (cont.)
• Frozen water (ice) is less dense than liquid
water, so ice floats.
• Unlike other substances, water expands
as it freezes.
Properties of Water (cont.)
Acids and Bases
• When water dissociates, it releases an
equal number of ions.
– Hydrogen ions (H+)
– Hydroxide ions (OH-)
H–O–H
H+ + OH-
Acids and Bases (cont.)
• Acidic solutions have a high H+
concentration.
• An acid is a substance that releases H+
when dissolved in water.
HCl
H+ + Cl-
Hydrochloric acid
Acids and Bases (cont.)
Acids and Bases (cont.)
• Basic solutions have a low H+
concentration.
• A base is a substance that releases OHwhen dissolved in water.
NaOH
Na+ + OH-
Sodium hydroxide
Acids and Bases (cont.)
pH and the pH scale
• The pH is a mathematical way of
indicating the number of H+ ions in a
solution.
• The pH scale is used to express acidity or
basicity (alkalinity).
Buffers and pH
• Within the body, the pH is kept in a narrow
range to maintain health.
• A buffer is a chemical or combination of
chemicals that keeps a pH within a given
range.
• Buffers resist changes in pH by taking up
+
extra H or OH from solution.
Buffers and pH (cont.)