Wednesday January 13th 1999
Announcements: None

Lecture notes:
 
Levels of Organization in Nature

Biosphere
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Ecosystem
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Community
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Population
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Multicellular Organism
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Organ System
^
Organ
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Tissue
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Cell
^
Organelle
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Molecule
^
Atom
^
Subatomic Particle

Elements: are materials that cannot be broken down into components with different properties.

Elements combine in fixed ways to form compounds (like molecules of water)

Mixtures: combinations of two or more elements of compounds mixed in similar but variable
amounts. Examples: sea water and air.

Atoms are the smallest portion of an element that still retains the properties of that element.

Parts of an atom: 1. Nucleus: the "core" of the atom.
a. contains: protons (+ charge)
b. contains: neutrons (0 charge)
c. contains almost all of the mass of the atom.

2. Electrons: shell of the atom.
a. electrons have a - charge
b. the electron cloud occupies almost all of the volume of the atom.

3. All neutral atoms have the same number of protons as electrons making
the net charge of a neutral atom 0.

Atomic Number is equal to the number of protons in the nucleus. It defines the element.

The Mass Number or Atomic Weight is the weighted average of the number of protons and neutrons in the atoms of an element.

Isotopes are atoms of the same element with a different number of neutrons. This is why the Mass Number isn't always 2x the atomic number.

1. Isotopes can be stable or unstable.
2. Unstable isotopes are called "radioactive" isotopes.
They decay and lose some of their nucleus and become different elements.
Example: Uranium becomes Lead.
Carbon ¹⁴ becomes Nitrogen (At. Wt. = 14)

Electron arrangement: Electrons are arranged around the nucleus in orbitals and shells.
These orbitals allow: 1. The electrons to stay as close
as possible to the nucleus.
2. As far away from each other as possible.
3. There is an finite number of electrons which
can occupy each energy level.

An ion is an atom which has either lost or gained electrons to give it a + or - charge.
Examples: Na⁺ Cl^- (table salt)

Gaining an electron = negative ion.
Losing an electron = positive ion.

The number of electrons in the outer shell of an atom and the "pull" of the protons in an atom determines: 1. Whether an atom donates and electron.
2. Whether an atom accepts and electron.
3. Whether an atom shares electrons.

Ionic Bonds: (the molecular equivalent to static cling)
1. Occurs when a positive and negative ion are linked by mutual attraction.
2. The electrons are not shared. Na⁺ Cl^- = NaCl

Covalent Bonds: When atoms share electrons to become a molecule.
Two types of covalent bonds
1. Non-polar covalent: each atom has and equal "pull" on the electron
2. Polar covalent: one atom exerts more "pull" so there is a slight difference
in the charge at one end of the molecule. Example: H₂O water.

Hydrogen Bonds: One molecule with polar covalent bonding (one end slightly negative) attracts
the slightly positive hydrogen in another polar covalent molecule.
Example: water

Hydrophobic: (water hating) These molecules are non-polar and do not form hydrogen bonds.
They hate water so much that they do not mix.
Example: the oil in oil and vinegar dressing.

Hydrophilic: (water loving) These are water loving molecules. They are polar molecules they
dissolve in water and can engage in various degrees of hydrogen bonding.
Example: alcohol and water.

Condensation: Covalent linking of some small molecules which involves the formation of water.

Hydrolysis: Breaking of bonds in large molecules. Water is needed to attach the fragments.