Basic Chemistry Review

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Basic Chemistry Review
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Chemical Context of Life

• Organisms composed of matter
• Matter takes up space and has mass
• Matter is made up of elements
• Elements cannot be broken down into other
  substances
• Compounds consists of 2 or more different
  elements in fixed ratio
• Ex. NaCl
• Essential Elements of Life CHNOPSCaK

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Atomic Structure

• Atoms smallest unit of matter
• Subatomic particles
• electrons (-), protons(), neutrons (0)
• Atomic number - of protons
• Atomic Mass - p n
• Ex. N

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Isotopes

• Isotopes atoms with more neutrons
• Ex. 99 of C is carbon-12 or 12C
• 13C or rarely found 14C
• Radioactive isotope occurs when the nucleus
  decays giving off particles and energy, when it
  loses protons it transforms into another element
• Date fossils based on rate of decay
• Radioactive tags trace substances
• PET scan

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Energy Levels

• Energy the capacity to cause change
• Potential E vs. Kinetic E
• The more distant from the nucleus, the greater
  their potential E
• Energy levels states of potential E,
  represented by electron shells
• Valence shell outermost shell, contains valence
  electrons

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Chemical Bonds

• Chemical bonds attraction between 2 or more
  atoms
• Driving force to have full valence shell
• Covalent bonds (molecules)
• Electronegativity strength of attraction
• Ionic Bonds (ions)
• Hydrogen bonds (weak)
• Van der Waals interactions (very weak)

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Covalent Bonds

• Sharing of a pair of valence electrons by 2 atoms
  creating molecule Ex. H2
• Shell diagram or Lewis Dot
• Structural formula
• Molecular formula
• 2 types
• Nonpolar covalent e shared equally
• Polar covalent unequal sharing due to
  differences of electronegativity
• Ex. H2O

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Ionic Bonds

• The electronegativity is so strong, an atom can
  take an e away from another atom, creating
  charged particles called ions
• Cation () ion
• Anion (-) ion
• Opposite charges attract to form an ionic bond,
  compounds called salts

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Hydrogen Bonds

• Hydrogen bond is the weak attraction between d
  of H and d- of O or N of a different molecule

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Van der Waals Interactions

• Electrons move creating weak positive and
  negatively charged regions (even if non-polar)

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Chemical Reactions

• Chemical Rxn the making or breaking of chemical
  bonds leading to changes in matter
• Reactants starting materials
• Products end result
• Coefficients number of molecules involved
• Reversible reactions
• Chemical equilibrium - stabilized

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Water Supports all Life

• 75 of Earths surface is water
• Cells are 70 95 water!
• Water is a polar molecule
• Molecules of water held together by H-bonds

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Properties of Water

• Cohesion H bonds holding H2O together
• Adhesion clinging to other substances
• Capillary Action transport against gravity
• Surface Tension how difficult it is to break the
  surface of a liquid

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Properties of Water (contd)

• Moderate Temperature
• Heat passes from the warmer to the cooler object
  until stabilizes
• Temperature measured in Celsius scale
• Water freezes at 00C and boils at 1000C, Human
  Body Temp is 370C
• Specific Heat amount of heat that must be
  absorbed or lost for 1g of substance to change
  10C
• Calorie amount of heat to raise 1g of water by
  10C
• Waters specific heat is high 1cal/g/0C due to H
  bonds
• Therefore water resists changes in temperature
• Water also has a high heat of vaporization helps
  moderate climate
• Evaporative cooling prevents organisms from
  overheating

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Properties of Water (contd)

• Expansion upon Freezing
• Less dense as a solid than a liquid
• Water condenses until 40C then expands
• Ice floats insulating the water below and
  allowing life to exist in aquatic ecosystems

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Properties of Water (contd)

• Versatility as a Solvent
• Solute substance being dissolved
• Solvent dissolving agent
• Solution homogenous mixture of 2 or more
  substances
• Aqueous solution water is solvent
• Water forms a hydration shell around ionic
  compounds
• Water also dissolves polar compounds
• Hydrophilic any substance w/affinity for H2O
• Hydrophobic repel water (nonpolar)

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Determine Solute Concentration in Aqueous
Solutions

• Calculate Molarity mol of solute/ L solution
• First, determine molecular mass of molecule by
  adding all atomic masses in molecule
• Then, determine molar mass
• 1 Mol 6.02 x 1023 molecular mass in g

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Acids and Bases

• Dissociation of Water (reversible)
• Hydrogen ion (H) transferred to another molecule
• Left w/ Hydroxide ion (OH-)
• Acid increases H conc.
• Ex. HCl
• Base reduces H conc.
• Ex. NaOH
• Strong acids and bases dissociate completely when
  mixed w/ water

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The pH scale

• In any aqueous solution at 250C
• HOH- 10 -14
• pH -log H
• Ex. For pure water H 10-7
• -log10-7 7
• pH declines as H increases

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Buffers

• Internal pH of most cells is about 7
• Changes in pH can be harmful to cells
• Buffers minimize changes in concentrations of
  H and OH- in a solution
• Work by accepting excess H in an acidic solution
  or donating H in a basic solution. Most contain
  a weak acid and its corresponding base.