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Chapter 2 Outline - Chapter2: 2. o o

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Chapter 2: The Chemical Context of Life 2.1 – Matter consists of chemical elements in pure form and in combinations called compounds  Organisms are composed of  matter . o Matter anything that takes up space and has mass Elements and compounds  o Matter is made up of  elements . Element —a substance that cannot be broken down to other substances by chemical  reactions o There are 92 elements recognized as occurring in nature.  o Compound —a substance consisting of two or more different elements combined in a fixed  ratio. Ex. Table Salt=Sodium Chloride= (NaCl) A compound characteristics different than an element Essential Elements of Life  o About 25 of the 92 natural elements are known to be essential to life.  [Memorize S.P.O.N.C.H: (Sulfur, Phosphorus, Oxygen, Nitrogen, Carbon, and  Hydrogen)] O.N.C.H makes up 96% of the body o Trace elements— elements required by an organism in only minute quantities  Ex. Iron (Fe) is needed by all forms of life  Ex. Iodine (I) is essential for vertebrates  2.2 – An element’s properties depend on the structure of its atoms  Each element consists of a certain kind of  atom  that is different from the  atoms  of any other  element. o Atom— the smallest unit of matter that still retains the properties of an element Subatomic Particles o Protons— Positive charge o Electron— Negative charge o Neutron —electrically neutral  o Atomic Nucleus— the center of the atom that is packed tightly with protons and neutrons   Protons give the core a positive charge o Electrons form  assort of cloud of negative charge around the nucleus  o Dalton— unit of measurement used to measure atoms and subatomic particles (also called  atomic mass unit, or amu) Neutrons and protons = about 1 dalton each Electrons = about 1/200 of a Dalton, so when calculating mass of an atom, electron mass  is omitted Atomic Number and Atomic Mass
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o Atomic Number —number of protons unique to an element that is written as a subscript to  the left of the symbol for the element Because the positive electric charge created by protons must be balanced by a negative  charge, the number of electrons is the same as the number of protons  Ex.  2 He  o Mass Number— sum of protons plus neutrons in the nucleus of an atom; this is written as  superscript to the left of an elements symbol  Ex.  4 2 He  o You can figure out the number of neutrons by  subtracting the atomic number from the mass  number Ex.  4 2 He, has two neutrons  o Atomic mass— total mass of an atom  Ex.  23 11 Na is 23 Daltons Isotopes
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