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Chemistry Edited

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Chemistry Edited Chemistry Edited Presentation Transcript

  • CHEMISTRY
  • Composition of Matter
    • Matter - Everything in universe is composed of matter
      • Matter is anything that occupies space or has mass
        • Mass – quantity of matter an object has
        • Weight – pull of gravity on an object
  • Elements
    • Pure substances that cannot be broken down chemically into simpler kinds of matter
    • More than 100 elements (92 naturally occurring)
    View slide
    • 90% of the mass of an organism is composed of 4 elements (oxygen, carbon, hydrogen and nitrogen)
    • Each element unique chemical symbol
      • Consists of 1-2 letters
      • First letter is always capitalized
    View slide
  • Atoms
    • The simplest particle of an element that retains all the properties of that element
    • Properties of atoms determine the structure and properties of the matter they compose
    • Our understanding of the structure of atoms based on scientific models not observation
  • The Nucleus
    • Central core
    • Consists of positive charged protons and neutral neutrons
    • Positively charged
    • Contains most of the mass of the atom
  • The Protons
    • All atoms of a given element have the same number of protons
    • Number of protons called the atomic number
    • Number of protons balanced by an equal number of negatively charged electrons
  • The Neutrons
    • The number varies slightly among atoms of the same element
  • The Electrons
    • Negatively charged high energy particles with little mass
    • Travel at very high speeds at various distances (energy levels) from the nucleus
      • Electrons in the same energy level are approximately the same distance from the nucleus
      • Outer energy levels have more energy than inner levels
      • Each level holds only a certain number of electrons
  • Compounds
    • Most elements do not exist by themselves
    • Readily combine with other elements in a predictable fashion
    • A compound is a pure substance made up of atoms of two or more elements
      • The proportion of atoms are always fixed
    • Chemical formula shows the kind and proportion of atoms of each element that occurs in a particular compound
    • The physical and chemical properties of a compound differ from the physical and chemical properties of the individual elements that compose it
    • The tendency of elements to combine and form compounds depends on the number and arrangement of electrons in their atoms
    • Atoms are most stable when their outer most energy level is filled
    • Most atoms are not stable in their natural state
    • Tend to react (combine) with other atoms in order to become more stable (undergo chemical reactions)
    • In chemical reactions bonds are broken; atoms rearranged and new chemical bonds are formed
  • Covalent Bonds
    • Formed when two atoms share one or more pairs of electrons
    • Molecules are the simplest part of a substance that retains all of the properties of the substance and exists in a free state
    • Some molecules are large and complex
  • Ionic Bonds
    • Some atoms become stable by losing or gaining electrons
    • Atoms that lose electrons are called positive ions
    • Atoms that gain electrons are called negative ions
    • Because positive and negative electrical charges attract each other ionic bonds form
  • States of Matter
    • Atoms are in constant motion
    • The rate at which atoms or molecules in a substance move determines its state
      • Solid
        • Molecules tightly linked together in a definite shape
        • Vibrate in place
        • Fixed volume and shape
      • Liquids
        • Molecules not as tightly linked as a solid
        • Maintain fixed volume
        • Able to flow and conform to shape of container
      • Gas
        • Molecules have little or no attraction to each other
        • Fill the volume of the occupied container
        • Move most rapidly
    • To cause a substance to change state, thermal energy must be added to or removed from a substance
  • Solutions
    • A solution is a mixture in which 2 or more substances are uniformly distributed in another substance
    • Solute is the substance dissolved in the solution
      • Particles may be ions, atoms, or molecules
    • Solvent is the substance in which the solute is dissolved
    • Solutions can be composed of varying proportions of a given solute in a given solvent --- vary in concentration (measurement of the amount of solute)
    • A saturated solution is one in which no more solute can be dissolved
    • Aqueous solution (water) are universally important to living things
  • Acids and Bases
    • One of the most important aspects of a living system is the degree of acidity or alkalinity
    • Dissociation of water
      • Breaking apart of the water molecule into two ions of opposite charge (due to strong attraction of oxygen atom of one molecule for H atom of another water molecule)
      • H 2 O  H + (hydrogen ion) + OH - (hydroxide ion)
  • Acids
    • Number of hydronium ions in solutions is greater than the number of hydroxide ions
        • HCl  H + + Cl -
  • Bases
    • Number of hydroxide ions in solution is greater than the number of hydronium ions
        • NaOH  Na + + OH -
  • pH Scale
    • logarithmic scale for comparing the relative concentrations of hydronium ions and hydroxide ions in a solution
    • ranges from 0 to 14
    • the lower the pH the stronger the acid
    • the higher the pH the stronger the base
    • pH 7.0 is neutral
  • Buffers
    • Control of pH is very important
    • Most enzymes function only within a very narrow pH
    • Control is accomplished with buffers
    • Buffers neutralize small amounts of either an acid or base added to a solution
    • Complex buffering systems maintain the pH values of your body’s many fluids at normal and safe levels