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Learning Outline

Introductory Chemistry

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Pre-A&P (BIO 095)

Chemistry is the basis for biology

Basic structural concepts

  • Atom: smallest part of a pure substance, or element, that still has the properties of that substance
  • Molecule: a particle made up of one or more atoms bound together
  • Element: a pure substance, made entirely of one kind of atom (all known elements are listed in the Periodic Table)
  • Compound: substance made of molecules that contain more than one kind of atom

Atomic structure and function video

  • Many different models exist; none are perfect slide
    • We’ll look at the Bohr model and electron cloud model first —then later structural and space-filling models
    • Bohr model (named for Niels Bohr) shows electrons orbiting the nucleus like planets orbit the sun
    • Electron cloud model (ECM) shows electrons as a cloud surrounding the nucleus
  • Nucleus
    • Protons have positive (+) charge; number of protons is “atomic number” and signifies kind of atom (which element)
    • Neutrons have no charge; optional and variable in number (isotopes)
  • Electrons
    • Electrons have a negative (-) charge and do not affect the type of element
    • Electrons may be present in regions called energy levels
      • The further from the nucleus, the more energy is needed by the electron to stay there –so the higher energy levels are farther from the nucleus
      • The lowest (first) energy level can contain up to two electrons
        • The next few can hold up to eight electrons each (the “octet rule”)
      • Energy levels fill from the inside out
Bohr model

Bohr model (hydrogen atom)

Bohr oxygen

Bohr model of oxygen atom (s and p are suborbitals) Credit

Energy levels

Electrons move to new energy levels as they gain or lose energy (squiggly arrow)

Electron cloud model (helium)

Electron cloud model (helium)

Behavior of atoms: chemical bonds slide

  • Atoms want to be “happy”—meaning having a full outer energy level
  • One path to happiness: ionic bonds
    • Occurs when an atom gives one or two electrons to another atom, giving both “full” outer energy levels
    • Ion: charged particle (atom or group of atoms)
    • Ions “stick” together because opposite charges attract —forming a bond
    • Electrolyte: molecule that dissolves in water to form ions
      • Sometimes the individual, dissolved ions are also called electrolytes
  • Another path to happiness: covalent bonds video
    • Outer level is “valence” level (from Latin word for outer garment)
    • Occurs when atoms share valence electrons (co-valent, get it?)
    • Sharing may not be equal slide
      • Polar molecules occur when sharing is NOT equal
        • Polar molecules are hydrophilic, or “get along with water”
        • Ions also “get along with water”
      • Nonpolar molecules occur when sharing IS equal
        • Nonpolar molecules are often hydrophobic, “don’t get along with water” slide

Other attractions

  • Sometimes also referred to as “bonds” or “weak attractions”
  • Hydrogen bonds (formed when polar molecules stick together) slide icon
  • Other weak attractions from temporary shifts in charge within molecules


  • Water is cohesive—hydrogen bonds make it “sticky” slide
  • May be represented H2O or H-O-H or HOH image
  • Solvent: something in which other molecules (solutes) are dissolved image
  • Solution: mixture of solutes dissolved in a fluid solvent

pH: acids, bases, and buffers slide

  • Water molecules may dissociate into H+ and OH
    • H+ is the hydrogen ion
    • OH is the hydroxide ion
  • Solutions with equal proportion of H+ and OH are “neutral”
  • Acids: solutions with higher proportion of H+
  • Bases: solutions with a lower proportion of H+ (alkaline solutions)
  • Can be expressed as “power of Hydrogen” or pH
    • pH scale is an inverse (base 10) logarithm of relative H+ concentration
    • 7 = neutral
    • acid = anything lower than 7
    • base = anything higher than 7
    • human blood plasma = pH 7.35-7.45
  • Buffer: system of molecules that absorb or release H+ —maintaining a relatively stable pH

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Last updated: July 7, 2017 at 21:02 pm