CHEMISTRY

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CHEMISTRY
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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

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Elements

• Pure substances that cannot be broken down
  chemically into simpler kinds of matter
• More than 100 elements (92 naturally occurring)

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• 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

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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

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The Nucleus

• Central core
• Consists of positive charged protons and neutral
  neutrons
• Positively charged
• Contains most of the mass of the atom

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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

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The Neutrons

• The number varies slightly among atoms of the
  same element
• Different number of neutrons produces isotopes of
  the same element

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Atomic Mass

• Protons neutrons are found in the nucleus of an
  atom
• Protons and neutrons each have a mass of 1 amu
  (atomic mass unit)
• The atomic mass of an atom is found by adding the
  number of protons neutrons in an atom

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The Electrons

• Negatively charged high energy particles with
  little or no mass
• Travel at very high speeds at various distances
  (energy levels) from the nucleus

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• 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

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Energy Levels

• Atoms have 7 energy levels
• The levels are K (closest to the nucleus), L, M,
  N, O, P, Q (furthest from the nucleus)
• The K level can only hold 2 electrons
• Levels L Q can hold 8 electrons (octet rule)

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Periodic Table

• Elements are arranged by their atomic number on
  the Periodic Table
• The horizontal rows are called Periods tell the
  number of energy levels
• Vertical groups are called Families tell the
  outermost number of electrons

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Compounds

• Most elements do not exist by themselves
• Readily combine with other elements in a
  predictable fashion

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• 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

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• 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

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Chemical Formulas

• Subscript after a symbol tell the number of atoms
  of each element
• H20 has 2 atoms of hydrogen 1 atom of oxygen
• Coefficients before a formula tell the number of
  molecules
• 3O2 represents 3 molecules of oxygen or (3x2) or
  6 atoms of oxygen

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• The physical and chemical properties of a
  compound differ from the physical and chemical
  properties of the individual elements that
  compose it

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• The tendency of elements to combine and form
  compounds depends on the number and arrangement
  of electrons in their outermost energy level
• Atoms are most stable when their outer most
  energy level is filled

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• 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 that
  store energy

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Covalent Bonds

• Formed when two atoms share one or more pairs of
  electrons

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Ionic Bonds

• Some atoms become stable by losing or gaining
  electrons
• Atoms that lose electrons are called positive ions

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• Atoms that gain electrons are called negative
  ions
• Because positive and negative electrical charges
  attract each other ionic bonds form

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Energy and Matter

• Energy
• The ability to do work or cause change
• Occurs in various forms
• Can be converted to another form
• Forms important to biological systems are
  chemical, thermal, electrical and mechanical
  energy
• Free energy is the energy in a system that is
  available for work

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States of Matter

• Atoms are in constant motion
• The rate at which atoms or molecules in a
  substance move determines its state

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• Solid
• Molecules tightly linked together in a definite
  shape
• Vibrate in place
• Fixed volume and shape

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• Liquids
• Molecules not as tightly linked as a solid
• Maintain fixed volume
• Able to flow and conform to shape of container

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• 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 (heat) must be added to or removed from a
  substance

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Energy and Chemical Reactions

• Living things undergo thousands of chemical
  reactions as part of the life process

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• Many are very complex involving multistep
  sequences called biochemical pathways
• Chemical equations represent chemical reactions
• Reactants are shown on the left side of the
  equation
• Products are shown on the right side

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• The number of each kind of atom must be the same
  on either side of the arrow (equation must be
  balanced)
• Bonds may be broken or made forming new compounds

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Energy Transfer

• Much of the energy organisms need is provided by
  sugar (food)
• Undergoes a series of chemical reactions in which
  energy is released (cell respiration)
• The net release of free energy is called an
  exergonic (exothermic) reaction

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• Reactions that involve a net absorption of free
  energy are called endergonic (endothermic)
  reactions
• Photosynthesis is an example
• Most reactions in living organisms are
  endergonic therefore living organisms require a
  constant source of energy

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• Most chemical reactions require energy to begin
• The amount of energy needed to start the reaction
  is called activation energy

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• Certain chemical substances (catalysts) reduce
  the amount of activation energy required
• Biological catalysts are called enzymes

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• Enzymes are an important class of catalysts in
  living organisms
• Mostly protein
• Thousands of different kinds
• Each specific for a different chemical reaction

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Enzyme Structure

• Enzymes work on substances called substrates
• Substrates must fit into a place on an enzyme
  called the active site
• Enzymes are reusable!

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Reduction-Oxidation Reactions

• Many of the chemical reactions that help transfer
  energy in living organisms involve the transfer
  of electrons (reduction-oxidation redox
  reactions)

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• Oxidation reaction reactant loses electron(s)
  becoming more positive

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• Reduction reaction reactant gains electron(s)
  becoming more negative

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Solutions
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Solutions

• A solution is a mixture in which 2 or more
  substances are uniformly distributed in another
  substance

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• 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
• Water is the universal solvent

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• 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

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• 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)
• H2O ? H (hydrogen ion) OH- (hydroxide ion)
• H H2O ? H3O (hydronium ion)

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Acids and Bases

• One of the most important aspects of a living
  system is the degree of acidity or alkalinity

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Acids

• Number of hydronium ions in solutions is greater
  than the number of hydroxide ions
• HCl ? H Cl-

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Bases

• Number of hydroxide ions in solution is greater
  than the number of hydronium ions
• NaOH ? Na OH-

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pH Scale

• logarithmic scale for comparing the relative
  concentrations of hydronium ions and hydroxide
  ions in a solution
• ranges from 0 to 14

• Each pH is 10X stronger than next
• e.g. ph 1 is 10 times stronger than ph 2

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• the lower the pH the stronger the acid
• the higher the pH the stronger the base
• pH 7.0 is neutral

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Buffers

• Control of pH is very important
• Most enzymes function only within a very narrow
  pH
• Control is accomplished with buffers made by the
  body
• Buffers keep a neutral pH (pH 7)

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• Buffers neutralize small amounts of either an
  acid or base added to a solution
• Complex buffering systems maintain the pH values
  of your bodys many fluids at normal and safe
  levels

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