1. Chapter 2 The Chemical Context of Life
The three subatomic particles and their significance.
The types of bonds, how they form, and their relative strengths
Domains of Study
Domain of BioMolecules
Domain of Cells
Domain of Organisms
Domain of Populations
Domain of Communities

2. Overview
Living organisms and the world they live in are subject to the basic laws of physics and chemistry.
Biology is a multidisciplinary science, drawing on insights from other sciences.
Life can be organized into a hierarchy of structural levels.
At each successive level, additional emergent properties appear.

3. The Basics Everything is made of matter Matter is made of atoms
Matter is anything that takes up space and has mass.
Atoms are made of:
protons + mass of nucleus
neutrons 0 mass of nucleus
electrons - mass << orbits
Different kinds of atoms = elements

4. The World of Elements

5. An element is a pure substance that cannot be broken down into other substances by chemical reactions.
There are 92 naturally occurring elements.
Each element has a unique symbol, usually the first one or two letters of the name. Some of the symbols are derived from Latin or German names.

6. A compound is a pure substance consisting of two or more elements in a fixed ratio.
Table salt (sodium chloride or NaCl) is a compound with equal numbers of atoms of the elements chlorine and sodium.

7. Models of atoms Atoms have volume and mass.
Mass of one proton or one neutron = atomic mass unit (amu) or 1 dalton, or 1.7 × 10–24 grams.
Mass of one electron = 9 × 10–28—usually ignored

8. Atomic structure determines behavior
The number of protons in an atom determines the element
# of protons = atomic number
this also tells you # of electrons, if neutral
# of neutrons = atomic mass- atomic #
All atoms of an element have same chemical properties
all behave the same
properties don’t change

9. Life requires ~25 chemical elements
About 25 elements are essential for life
Four elements make up 96% of living matter:
• carbon (C) • hydrogen (H)
• oxygen (O) • nitrogen (N)
Four elements make up most of remaining 4%:
• phosphorus (P) • calcium (Ca)
• sulfur (S) • potassium (K)

11. Isotopes
Isotopes: forms of an element with different numbers of neutrons, thus different mass numbers
Example:
12C has 6 neutrons
13C has 7 neutrons
14C has 8 neutrons

12. Radioactive Isotopes Spontaneously give off particles and energy
Alpha, beta, gamma radiation

13. How does this atom behave?
Bonding properties
Effect of electrons
chemical behavior of an atom depends on its electron arrangement
depends on the number of electrons in its outermost shell, the valence shell
How does this atom behave?

14. The Energy Levels of Electrons
Is defined as the capacity to cause change
Potential energy
Is the energy that matter possesses because of its location or structure
A ball bouncing down a flight
of stairs provides an analogy
for energy levels of electrons,
because the ball can only rest
on each step, not between
steps.
(a)
Figure 2.7A

15. How does this atom behave? How does this atom behave?
Bonding properties
Effect of electrons
chemical behavior of an atom depends on number of electrons in its outermost shell
How does this atom behave?
How does this atom behave?

16. Elements & their valence shells
Elements in the same row have the same number of shells

17. Elements & their valence shells
Elements in the same column have the same valence & similar chemical properties
Oxygen has medium electronegativity so doesn’t pull electrons all the way off hydrogen whereas chlorine would.
So oxygen forms a polar covalent bond.
Carbon has only a weak electronegativity so forms a nonpolar covalent bond

18. Elements & their valence shells
Moving from left to right, each element has a sequential addition of electrons (and protons)

19. Chemical reactivity Atoms tend to
Complete a partially filled outer (valence) electron shell or
Empty a partially filled outer (valence) electron shell
This tendency drives chemical reactions

21. Electron Configuration and Chemical Properties
Orbitals occur in series called electron shells or energy levels.
First shell: one orbital—s orbital
Second shell: one s and three p orbitals (holds eight electrons)
Third shell: one s and three p orbitals (holds eight electrons)
Fourth & Fifth Shells: d orbitals added (10 more electrons)
Seventh & Eighth Shells: f orbitals added (16 more electrons)

22. Ionic bonds

23. “Let’s go to the video tape!”
Ionic bonds
“Let’s go to the video tape!”
Play Video
Transfer of an electron
Forms + & - ions
+ = cation
– = anion
Weak bond
example:
salt = dissolves easily in water

24. “Let’s go to the video tape!”
Play Video
Covalent bonds
Two atoms need an electron
Share a pair of electrons
Strong bond
both atoms holding onto the electrons
Forms molecules
example:
water = takes energy to separate

25. Double covalent bonds
Two atoms can share more than one pair of electrons
double bonds (2 pairs of electrons)
triple bonds (3 pairs of electrons)
Very strong bonds

26. Multiple covalent bonds
1 atom can form covalent bonds with two or more other atoms
forms larger molecules
ex. carbon
Methane
Symmetrical molecule
• leads to some of its properties
• Charges are balanced
• Leads to little attraction between different methane molecules
• Therefore methane is a gas at room temperature

27. “Let’s go to the video tape!”
Hydrogen bonds
Positive H atom in 1 water molecule is attracted to negative O in another
Can occur wherever an -OH exists in a larger molecule
Weak bonds
“Let’s go to the video tape!”
Play Video

28. Polar covalent bonds Pair of electrons not shared equally by 2 atoms
Water = O + H
oxygen has stronger “attraction” for the shared electrons than hydrogen
oxygen has higher electronegativity

29. Polar covalent bonds 2 hydrogens in the water molecule form an angle
Water molecule is polar
oxygen end is –
hydrogen end is +
Leads to many interesting properties of water….

30. Van der Waals Interactions
Occur when transiently positive and negative regions of molecules attract each other

31. Strong and weak chemical bonds

32. Structure and Function run from large scale body systems through molecules and atoms. Structure and function are what Enzymes are all about
Morphine
Carbon
Hydrogen
Nitrogen
Sulfur
Oxygen
Natural
endorphin
(a) Structures of endorphin and morphine. The boxed portion of the endorphin molecule (left) binds to receptor molecules on target cells in the brain. The boxed portion of the morphine molecule is a close match.
(b) Binding to endorphin receptors. Endorphin receptors on the surface of a brain cell recognize and can bind to both endorphin and morphine.
Endorphin
receptors
Brain cell
Figure 2.17

33. Chemical reactions make and break chemical bonds
Convert reactants to products
Reactants
Reaction
Product
2 H2 O2
2 H2O +

34. Life is the result of Chemical Reactions
Photosynthesis
Is an example of a chemical reaction
Figure 2.18

35. Chemical Equilibrium Chemical equilibrium
Is reached when the forward and reverse reaction rates are equal

36. Reductionist view of biology
Matter is made of atoms
Life requires ~25 chemical elements
Atomic structure determines behavior of an element
Atoms combine by chemical bonding to form molecules
Weak chemical bonds play important roles in chemistry of life
A molecule’s biological function is related to its shape
Chemical reactions make & break chemical bonds