1. CHAPTER 2 The Chemical Basis of Life

2. ATOMS AND MOLECULES The emergence of biological function starts at the chemical level
Everything an organism is and does depends on chemistry
Chemistry is in turn dependent on the arrangement of atoms in molecules

3. Molecules and ecosystems are at opposite ends of the biological hierarchy
Each level of organization in the biological hierarchy builds on the one below it
At each level, new properties emerge

4. Elements About 25 different chemical elements are essential to life
An element is a substance that can’t be broken down into simpler chemical substances.
About 25 different chemical elements are essential to life
Carbon, hydrogen, oxygen, and nitrogen make up more that 96 percent of the mass of a human body.
Trace elements: such as iron and copper, play a vital role in maintaining healthy cells in all organisms.

5. 2.2 CONNECTION: Trace elements are common additives to food and water
Several chemicals are added to food for a variety of reasons
Help preserve it
Make it more nutritious
Make it look better
Check out the “Nutrition Facts” label on foods and drinks you purchase
Student Misconceptions
1. The dangers posed by certain chemicals in our food and broader environment often misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals.
Teaching Tips
1. Students might be interested in the following aside: One of the challenges of raising captive, exotic animals is meeting the unique dietary requirements of a species. A zoo might have trouble keeping a particular animal because zoologists have not identified all of the trace elements required in the animal’s diet.
2. Many breakfast cereals are fortified with iron. As noted in Module 2.2, you can crush the cereal and extract distinct iron particles with a magnet. An overhead projector or video imaging device should clearly reveal the iron particles stuck to the magnet. This short practical demonstration can help connect an abstract concept to a concrete example.
Copyright © 2009 Pearson Education, Inc.

6. Elements can combine to form compounds
Chemical elements combine in fixed ratios to form compounds
Example: sodium + chlorine  sodium chloride

7. Atoms: The Building Blocks of Elements
An atom is the smallest particle of an element that has the characteristics of that element.
Atoms are the basic building blocks of all matter.
Different elements have different types of atoms

8. Atoms consist of protons, neutrons, and electrons
An atom is made up of protons ( + charge) and neutrons (no charge) located in a central nucleus
The nucleus is surrounded by electrons ( - charge)

9. Isotopes of an Element
Atoms of each element are distinguished by a specific number of protons
The number of neutrons may vary
Variant forms of an element are called isotopes
Some isotopes are radioactive

10. Connection: Radioactive isotopes can help or harm us
Radioactive isotopes can be useful tracers for studying biological processes
PET scanners use radioactive isotopes to create anatomical images
PET scan of an alzheimer's patient
PET scan of a normal brain

11. 2.5 CONNECTION: Radioactive isotopes can help or harm us
In addition to benefits, there are also dangers associated with using radioactive substances
Uncontrolled exposure can cause damage to some molecules in a living cell, especially DNA
Chemical bonds are broken by the emitted energy, which causes abnormal bonds to form
One of the most serious environmental threats of radioactivity is radioactive fallout from nuclear accidents. A 1979 accident in the United States at the Three Mile Island nuclear power plant led to strict regulations about safety. In the Soviet Union on Saturday, April 26, 1986, the Number 4 reactor at the Chernobyl nuclear power plant blew apart and blasted through the surrounding concrete containment structure. Two workers died immediately in the blast, but over the following months 30 others died, most of them firefighters who battled to prevent the fire from spreading to the reactor in the next building. All died from radiation burns and radiation sickness following exposure to strong gamma and beta radiation.
Student Misconceptions
1. The dangers posed by certain chemicals in our food and broader environment often misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals.
Copyright © 2009 Pearson Education, Inc.

12. Electron arrangement determines the chemical properties of an atom
Electrons are arranged in shells
The outermost shell determines the chemical properties of an atom
In most atoms, a full outer shell holds eight electrons
Electrons occur in energy levels called electron shells
Information about the distribution of electrons is found in the periodic table of the elements
Atoms whose shells are not full tend to interact with other atoms and gain, lose, or share electrons

13. 2.6 Electron arrangement determines the chemical properties of an atom
Atoms want to fill their outer electron shells
To accomplish this, the atom can share, donate, or receive electrons
This results in attractions between atoms called chemical bonds
Chemical bonds cause atoms to stay close together. Recall that a compound is a substance consisting of two or more different elements combined in a fixed ratio. Chemical bonds are responsible for holding atoms together.
Student Misconceptions
1. The dangers posed by certain chemicals in our food and broader environment often misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals.
Copyright © 2009 Pearson Education, Inc.

14. Ionic bonds are attractions between ions of opposite charge
When atoms gain or lose electrons, charged atoms called ions are created
An electrical attraction between ions with opposite charges results in an ionic bond
Sodium and chloride ions bond to form sodium chloride, common table salt

15. Covalent bonds, the sharing of electrons, join atoms into molecules
Some atoms share outer shell electrons with other atoms, forming covalent bonds
Atoms joined together by covalent bonds form molecules

16. 2.9 Unequal electron sharing creates polar molecules
Atoms in a covalently bonded molecule continually compete for shared electrons
The attraction (pull) for shared electrons is called electronegativity
More electronegative atoms pull harder
Student Misconceptions
1. The dangers posed by certain chemicals in our food and broader environment often misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals.
Teaching Tips
1. Modules 2.9 and 2.10 discuss the special bonding in and between water molecules. Many students do not appreciate the importance of weak chemical bonds in water and cellular chemistry. Extra time and attention may be required to address this special aspect of chemistry.
Copyright © 2009 Pearson Education, Inc.

17. covalent bonds
Atoms in a covalently bonded molecule may share electrons equally, creating a nonpolar molecule
If electrons are shared unequally, a polar molecule is created

18. This makes the oxygen end of the molecule slightly negatively charged
In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen
This makes the oxygen end of the molecule slightly negatively charged
The hydrogen end of the molecule is slightly positively charged
Water is therefore a polar molecule

19. 2.10 Hydrogen bonds are weak bonds important in the chemistry of life
Some chemical bonds are weaker than covalent bonds
Hydrogen, as part of a polar covalent bond, will share attractions with other electronegative atoms
Examples are oxygen and nitrogen
Water molecules are electrically attracted to oppositely charged regions on neighboring molecules
Because the positively charged region is always a hydrogen atom, the bond is called a hydrogen bond
Student Misconceptions
1. The dangers posed by certain chemicals in our food and broader environment often misled people to associate chemicals with harm. People might not want chemicals added to their food or in their environment. Students often fail to appreciate the chemical nature of our bodies and our world and the potential harm or benefits of naturally occurring chemistry. They often fail to understand why natural does not necessarily mean good. (Consider presenting a long list of naturally occurring toxins to make this point.) Your class may benefit from a class discussion of these misconceptions about our attitudes toward chemicals.
Teaching Tips
1. Modules 2.9 and 2.10 discuss the special bonding in and between water molecules. Many students do not appreciate the importance of weak chemical bonds in water and cellular chemistry. Extra time and attention may be required to address this special aspect of chemistry.
Copyright © 2009 Pearson Education, Inc.