1. The Chemical Context of Life
Chapter 2
The Chemical Context of Life
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2. Chapter 2 The Chemical Context of Life
1. What is the hierarchy of life? (smallest to largest)

3. 6 Organs and organ systems 7 Tissues 10 Molecules
8 Cells
6 Organs and organ systems
7 Tissues
10 Molecules
9 Organelles
50 µm
10 µm
1 µm
Cell
Atoms

4. Figure 1.3 Exploring Levels of Biological Organization
1 The biosphere
2 Ecosystems
3 Communities
4 Populations
5 Organisms

5. Chapter 2 The Chemical Context of Life
What is the hierarchy of life? (smallest to largest)
What is an atom?
Smallest unit of matter that retains the physical & chemical properties of its element
Element – a substance that cannot be broken down into other substances by chemical rxn
What is an atom made of?
Proton – (+1) charge, found in nucleus, 1 amu
Neutron – no charge, found in nucleus, 1 amu
Electron – (-1) charge, orbit nucleus, mass negligible

6. Figure 2.4 Simplified models of a helium (He) atom
Cloud of negative
charge (2 electrons)
Electrons
Nucleus
(a)
(b)

7. Chapter 2 The Chemical Context of Life
What is an atom?
What is an atom made of?
What do these numbers mean?
23Na 12C
11Na 6C
What is an isotope? Radioisotope?
Atoms of an element that have the same atomic # but different atomic mass
Unstable isotope where the nucleus spontaneously decays emitting subatomic particles &/or energy as radioactivity.
5. What are radioisotopes used for?
Atomic mass - protons + neutrons
Atomic # - # of protons

8. Chapter 2 The Chemical Context of Life
What is an atom?
What is an atom made of?
What do these numbers mean?
What is an isotope? Radioisotope?
What are radioisotopes used for?
How are atoms held together?
What are the different types of strong bonds?
Covalent – sharing of electrons
Polar covalent – UNequal sharing
Non-polar covalent – equal sharing
Ionic – complete transfer of electrons
bonds

9. Chapter 2 The Chemical Context of Life
What is an atom?
What is an atom made of?
What do these numbers mean?
What is an isotope? Radioisotope?
What are radioisotopes used for?
How are atoms held together?
What are the different types of strong bonds?
What is electronegativity?
Atom’s ability to attract & hold electrons
In Biology – most concerned with N & O

10. Formation of a covalent bond
Hydrogen atoms (2 H)
Hydrogen
molecule (H2) +
In each hydrogen
atom, the single electron
is held in its orbital by
its attraction to the
proton in the nucleus. 1
When two hydrogen
atoms approach each
other, the electron of
each atom is also
attracted to the proton
in the other nucleus. 2
The two electrons
become shared in a
covalent bond,
forming an H2
molecule. 3
Figure 2.10

11. Single and double covalent bonds
Name
(molecular
formula)
Electron-
shell
diagram
Structural
formula
Space-
filling
model
Hydrogen (H2).
Two hydrogen
atoms can form a
single bond.
Oxygen (O2).
Two oxygen atoms
share two pairs of
electrons to form
a double bond. H O
Figure 2.11 A, B
(a)
(b)

12. Covalent bonding in compounds
Name
(molecular
formula)
Electron-
shell
diagram
Structural
formula
Space-
filling
model
(c)
Methane (CH4).
Four hydrogen
atoms can satisfy
the valence of
one carbon
atom, forming
methane.
Water (H2O).
Two hydrogen
atoms and one
oxygen atom are
joined by covalent
bonds to produce a
molecule of water.
(d) H O C
Figure 2.11 C, D

13. In a polar covalent bond
The atoms have differing electronegativities
Share the electrons unequally
This results in a
partial negative
charge on the
oxygen and a
partial positive
charge on
the hydrogens.
H2O d– O H d+
Because oxygen (O) is more electronegative than hydrogen (H),
shared electrons are pulled more toward oxygen. d–
Figure 2.12

14. Sodium chloride (NaCl)
An ionic bond
Is an attraction between anions and cations
Due to high electronegativity
Cl–
Chloride ion
(an anion) –
The lone valence electron of a sodium
atom is transferred to join the 7 valence
electrons of a chlorine atom. 1
Each resulting ion has a completed
valence shell. An ionic bond can form
between the oppositely charged ions. 2 Na Cl +
Sodium atom
(an uncharged
atom)
Chlorine atom
Na+
Sodium on
(a cation)
Sodium chloride (NaCl)
Figure 2.13

15. Hydrogen Bonds A hydrogen bond
Occurs between 2 molecules with polar covalent bonds
Forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom
 –
 +
Water
(H2O)
Ammonia
(NH3) O H
 +
 – N
A hydrogen
bond results
from the
attraction
between the
partial positive
charge on the
hydrogen atom
of water and
the partial
negative charge
on the nitrogen
atom of
ammonia. + d+
Figure 2.15
 +

16. Molecular shape
Determines how biological molecules recognize and respond to one another with specificity

17. Figure 2.17 Carbon Nitrogen Hydrogen Sulfur Oxygen Natural endorphin
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

18. Chapter 2 The Chemical Context of Life
What is an atom?
What is an atom made of?
What do these numbers mean?
What is an isotope? Radioisotope?
What are radioisotopes used for?
How are atoms held together?
What are the different types of strong bonds?
What is electronegativity?
How are bonds created between atoms?

19. What is chemical equilibrium?
Chemical reactions
Convert reactants to products
Reactants
Reaction
Product
2 H2 O2
2 H2O +
What is chemical equilibrium?

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