LECTURE 04 ATOMS, CHEMICAL BONDS, CARBON COMPOUNDS & WATER

LECTURE 04 ATOMS, CHEMICAL BONDS, CARBON COMPOUNDS &...

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2:010 Principles of Biology 1 LECTURE 4 Chemistry As you saw in lab last week there is a fundamental structural unit to all life forms. That is the cell and it can only be seen with a light microscope. In another course (Chemistry) you took as a prerequisite to this one, you studied another fundamental structural unit; that of physical matter. You called this the atom. There are 92 different types of atoms that exist in Nature. Each type is the fundamental structural unit for a different element. However, even a single atom is a complex system (network) of interacting subatomic particles. All atoms are made of the same types of particles; electrons (e - ), protons (p + ) and neutrons (n). What distinguishes the atoms of one element from those of another is the number of each type of subatomic particle. Atomic Number = number of e - = number of p + Atomic Mass = number of p + + number of n It is clear from these representations of atomic structure that most of the atom is empty space. Since you are made of atoms you too are mostly empty space. In fact, it has been estimated that if you condense all the atoms in your body to eliminate the empty space you would be left with a single object the size of a dust particle. 1
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What type of atoms are you made of? The x-axis is the atomic number of each of the elements. The y-axis represents the log of the relative abundance of each of the elements by weight. Oxygen (Z=8) is 65% Carbon (Z=6) is 18.5% All together these 4 elements make up 96% of the weight Hydrogen (Z=1) is 9.5% of your body. Nitrogen (Z=7) is 3.3% The other 4% is from P, Ca, S, K, Na, Mg, Cl In contrast, oxygen and silicon (Z=14) are the most abundant elements in the Earth’s crust. With high levels of Al, Ca, K, and Cr. The solar system is 90% Hydrogen with Helium being the next most abundant element. 2
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The main conclusions from these elemental analyses are: 1. The elemental composition of life forms is quantitatively different from that of non-living matter in the Earth’s crust and in the solar system. 2. The elemental composition of life forms is NOT qualitatively different from that of non-living matter. There are no unique elements that are only present in organisms. No evidence of a unique type of living matter as described by vitalists. Why does life have its particular elemental composition? Why is life carbon based? The answers to these questions may be found in the structure of the different elements is characterized by the distribution of electrons in shells around the nucleus. 3
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These electron shells are at various distances from the nucleus. The greater the distance the higher the potential energy. The lower energy (closer) shells are filled first. The outermost shell is the valence shell and contains the valence electron some of which
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This note was uploaded on 03/30/2008 for the course BIO 2:010 taught by Professor Denburg during the Spring '08 term at University of Iowa.

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LECTURE 04 ATOMS, CHEMICAL BONDS, CARBON COMPOUNDS &...

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