Chapter 2 - Chemical Basis of Life I

Chapter 2 - Chemical Basis of Life I - THE CHEMICAL BASIS...

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Click to edit Master subtitle style 4/30/11 THE CHEMICAL BASIS OF LIFE I:ATOMS,MOLECULES, AND WATER CHAPTER 2
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4/30/11 All living organisms are a collection of atoms and molecules. Atoms n Atoms are nature’s building material. n Matter : Anything that has mass and occupies space n Smallest functional units of matter that form all chemical substances and that cannot be further broken down into other substances by ordinary chemical or physical means. Matter is composed of extremely small particles called atoms. n Each specific type of atom is a chemical element
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4/30/11 Three subatomic particles Protons- positive, found in nucleus, same number as electrons Neutrons- neutral, found in nucleus, number can vary Electrons- negative, found in orbitals, same number as protons Entire atom has no net electric charge
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4/30/11 Electrons occupy orbitals Scientists initially visualized an atom as a mini solar system This is an oversimplified but convenient image Electrons travel within regions surrounding the nucleus (orbitals) in which the probability is high of finding that electron Can be depicted as a cloud - Niels Bohr in 1913
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4/30/11 Orbitals S orbitals are spherical P orbitals are propeller or dumbbell shaped Each orbital can hold only 2 electrons An atom with more than 2 electrons has more than 1 n Atoms with progressively more electrons have orbitals within electron shells that are at greater and greater distances from the center of the nucleus 1st shell - 1 spherical orbital (1s) - holds 2 electrons 2nd shell - 1 spherical orbital (2s) and 3 dumbbell-shaped orbitals (2p) – can hold 4 pairs of electrons
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4/30/11 Nitrogen An atom of nitrogen has seven protons and seven electrons 2 electrons fill 1st shell 5 electrons in 2nd shell 2 fill 2s orbital 1 each in the 3 p orbitals Outer 2nd shell is not full Electrons in the outer shell that are available to combine with other atoms are called the valence
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4/30/11 Protons Number of protons in an atom is its atomic number The atomic number is also equal to the number of electrons in the atom so that the net charge is zero Neutrons n The particles in the nucleus that have no charge.
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4/30/11 Periodic table Organized by atomic number Rows correspond to number of electron shells Columns, from left to right, indicate the numbers of electrons in the outer shell Similarities of elements within a column occur because they have the same number of electrons in their outer shells, and therefore they have similar chemical bonding properties
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Chapter 2 - Chemical Basis of Life I - THE CHEMICAL BASIS...

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