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Chemical Context of Life
2
...
5
H 9
...
3
96%
Ca 1
...
0
K 0
...
3
Na 0
...
2
Mg 0
...
2 An element’s properties depend on the structure of its atoms
Atom the smallest unit of matter that still retains the properties of an element
Subatomic particles go together to make an atom
Neutrons =
Protons +
Electrons Electrons are arranged in circular patterns, in electron shells
farthest away from the center have the most energy
closest to the center have the least energy
Third shell = highest energy
Second shell = higher energy level
First shell = lowest energy level
Atomic number number of protons in its nucleus
proton # = atomic identity
Mass number (daltons) = protons + electrons
Atomic mass atom’s total mass
*All atoms of an element have the same number of protons but may differ in number of neutrons
Isotopes are two atoms of an element that differ in number of neutrons
Stable isotopes in biological research are:
— Following contribution from different environmental sources
— Tracing elements through reactions
Radioactive isotopes decay spontaneously, giving off particles of energy; they occur naturally
— Dating fossils
— Tracing atoms through metabolic processes
— Diagnosing medical disorders
The chemical behavior of an atom is determined by the distribution of electrons in electron
shells
The periodic table organizes by shells number
First Shell
Hydrogen, Helium
Second Shell
Third Shell
Valence electrons are those in the outermost shell, or valence shell
Elements with a full valence shell are chemically inert

Orbital is the 3D space
2
...
H2O and NH3
If electrons are distributed asymmetrically in molecules or atoms, they can result in “hot spots”
of positive or negative charge
Van der Waals interactions are attractions between molecules that are close together as a result
of these charges
Collectively, such interactions can be strong, as between molecules of a gecko’s toe
hairs and a wall surface
H 2O

Carbon can form so many bonds at once
Molecules with similar shapes can have similar biological effects
Ex
...
4 Chemical reactions make an break chemical bonds
Chemical reactions are the making and breaking of chemical bonds
Reactants —Reaction—> Products
All chemical reactions are reversible
Chemical equilibrium is reached when the forward and reverse reaction rates are equal
Production of O2 by photosynthesis (6CO2 + 6H2O —> C6H12O6 + 6O2)
reactants

products

the reaction does not happen in one single step, there are actually many steps



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