Modern Biology TextbookHolt

Section 1 Composition of MatterChapter 2

• 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.

Section 1 Composition of MatterChapter 2

Matter is anything that occupies space and has mass.

Mass is the quantity of matter an object has.

Section 1 Composition of MatterChapter 2

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.

Section 1 Composition of MatterChapter 2

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.

Section 1 Composition of MatterChapter 2

• Electrons– Electrons move

about the nucleus in orbitals.

– An orbital is a three-dimensional region around a nucleus that indicates the probable location of an electron.

Section 1 Composition of MatterChapter 2

Isotopes◦ Atoms of the same

element that have a different number of neutrons are called isotopes.

Section 1 Composition of MatterChapter 2

Compounds

• Compounds consist of atoms of two or more elements that are joined by chemical bonds in a fixed proportion.

Section 1 Composition of MatterChapter 2

Compounds, continued

• Covalent Bonds– A covalent bond is

formed when two atoms share electrons.

Section 1 Composition of MatterChapter 2

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 2Section 1 Composition of Matter

Section 2 EnergyChapter 2

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.

Section 2 EnergyChapter 2

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.

Section 2 EnergyChapter 2

Energy and Chemical Reactions

• Reactants are substances that enter chemical reactions.

• Products are substances produced by chemical reactions.

Chapter 2Section 2 Energy

Section 2 EnergyChapter 2

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.

Section 3 Water and SolutionsChapter 2

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.

Section 3 Water and SolutionsChapter 2

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.

Section 3 Water and SolutionsChapter 2

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.

Section 3 Water and SolutionsChapter 2

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.

Section 3 Water and SolutionsChapter 2

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.

Section 3 Water and SolutionsChapter 2

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.

Section 3 Water and SolutionsChapter 2

Solutions

• A solution consists of a solute dissolved in a solvent.

Section 3 Water and SolutionsChapter 2

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.

Section 3 Water and SolutionsChapter 2

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.

Section 3 Water and SolutionsChapter 2

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 2Section 3 Water and Solutions