chapter 2 chemistry of life modern biology textbook holt
TRANSCRIPT
Section 1 Composition of MatterChapter 2
Objectives• 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
• 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 and Atoms
• 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
Elements and Atoms, continued
• 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
Elements and Atoms, continued
• 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
Elements and Atoms, continued
• 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.
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.
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.