Modern Biology Textbook
Holt
Chapter 2
Section 1 Composition of Matter
•
Define the term matter.
•
Explain the relationship between elements and
atoms.
•
Draw and label a model of the structure of an
atom.
•
Explain how compounds affect an atom’s
stability.
•
Contrast covalent and ionic bonds.
Chapter 2


Section 1 Composition of Matter
Matter is anything that occupies space and
has mass.
Mass is the quantity of matter an object has.
Chapter 2


Section 1 Composition of Matter
Elements are made of a single kind of atom
and cannot be broken down by chemical
means into simpler substances.
Atoms are composed of protons, neutrons,
and electrons.
Chapter 2

Section 1 Composition of Matter
The Nucleus
◦ Protons and neutrons make up the nucleus of the
atom.
◦ Protons are positively charged particles.
◦ Neutrons have no charge (neutral).
◦ Together the mass of the protons and neutrons in
the nucleus of an atom makes up the atom’s atomic
mass.
Chapter 2
•
Electrons
Section 1 Composition of Matter
– Electrons move about
the nucleus in orbitals.
– An orbital is a threedimensional region
around a nucleus that
indicates the probable
location of an electron.
Chapter 2

Section 1 Composition of Matter
Isotopes
◦ Atoms of the same
element that have a
different number of
neutrons are called
isotopes.
Chapter 2
Section 1 Composition of Matter
Compounds
• Compounds consist of atoms of two or more elements
that are joined by chemical bonds in a fixed proportion.
Chapter 2
Section 1 Composition of Matter
Compounds, continued
• Covalent Bonds
– A covalent bond is
formed when two
atoms share electrons.
Chapter 2
Section 1 Composition of Matter
Compounds, continued
• Ionic Bonds
– An ionic bond is formed when one atom gives up an
electron to another. The positive ion is then attracted
to a negative ion to form the ionic bond.
Chapter 2
Section 1 Composition of Matter
Chapter 2
Section 2 Energy
Objectives
• Describe the physical properties of each state of matter.
• Describe the role of reactants and products in chemical
reactions.
• Explain the relationship between enzymes and activation
energy.
• Explain how oxidation and reduction reactions are linked.
Chapter 2
Section 2 Energy
Energy and Matter
• States of Matter
– Addition of energy to
a substance can
cause its state to
change from a solid
to a liquid and
from a liquid to a gas.
Chapter 2
Section 2 Energy
Energy and Chemical Reactions
• Reactants are substances that enter chemical reactions.
• Products are substances produced by chemical reactions.
Chapter 2
Section 2 Energy
Chapter 2
Section 2 Energy
Energy and Chemical Reactions, continued
• Activation Energy
– Enzymes lower the amount of activation energy
necessary for a reaction to begin in living systems.
• Oxidation Reduction Reactions
– A chemical reaction in which electrons are exchanged
between atoms is called an oxidation-reduction
reaction.
Chapter 2
Section 3 Water and Solutions
Objectives
• Describe the structure of a water molecule.
• Explain how water’s polar nature affects its ability to
dissolve substances.
• Outline the relationship between hydrogen bonding and
the different properties of water.
• Identify the roles of solutes and solvents in solutions.
• Differentiate between acids and bases.
Chapter 2
Section 3 Water and Solutions
Polarity
• Water is considered to be a polar molecule due to an
uneven distribution of charge.
• The electrons in a water molecule are shared unevenly
between hydrogen and oxygen.
Chapter 2
Section 3 Water and Solutions
Polarity, continued
• Solubility of Water
– The polarity of water makes it effective at dissolving
other polar substances such as sugars, ionic
compounds, and some proteins.
Chapter 2
Section 3 Water and Solutions
Hydrogen Bonding
• A hydrogen bond is the
force of attraction
between a hydrogen
molecule with a partial
positive charge and
another atom or molecule
with a partial or full
negative charge.
Chapter 2
Section 3 Water and Solutions
Hydrogen Bonding, continued
• Cohesion and Adhesion
– Cohesion is an attractive force that holds molecules of
a single substance together, such as water molecules.
– Adhesion is the attractive force between two particles
of different substances, such as water molecules and
glass molecules.
Chapter 2
Section 3 Water and Solutions
Hydrogen Bonding, continued
• Temperature Moderation
– Water has the ability to absorb a relatively large
amount of energy as heat and the ability to cool
surfaces through evaporation.
• Density of Ice
– Solid water is less dense than liquid water due to the
shape of the water molecule and hydrogen bonding.
Chapter 2
Section 3 Water and Solutions
Solutions
• A solution consists of a solute dissolved in a solvent.
Chapter 2
Section 3 Water and Solutions
Acids and Bases, continued
• Ionization of Water
– Water ionizes into hydronium ions (H3O+) and
hydroxide ions (OH–).
• Acids
– Acidic solutions contain more hydronium ions than
hydroxide ions.
Chapter 2
Section 3 Water and Solutions
Acids and Bases, continued
• Bases
– Basic solutions contain more hydroxide ions than
hydronium ions.
• Buffers
– Buffers are chemicals that neutralize the effects of
adding small amounts of either an acid or a base to a
solution.
Chapter 2
Section 3 Water and Solutions
Acids and Bases, continued
• pH
– Scientists have developed a scale for comparing the
relative concentrations of hydronium ions and
hydroxide ions in a solution. This scale is called the pH
scale, and it ranges from 0 to 14.
Chapter 2
Section 3 Water and Solutions