The Chemical Context of Life

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The Chemical Context of Life

• Chapter 2

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The Chemical Context of Life

• What is an element?
• The basic form of matter that cannot be broken
  down
• What is a compound?
• Two or more different elements combined in a
  fixed ratio
• What is an atom?
• The smallest unit of an element that still has
  the properties of that element.

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Subatomic particles

• neutrons
• no charge
• found in the nucleus
• mass of 1 amu
• protons
• positive charge
• found in the nucleus
• mass of 1 amu
• electrons
• negative charge
• found outside the nucleus
• little mass

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Characteristics of Elements

• Atomic number Number of protons in the
  nucleus of an atom
• Mass number Number of protons plus the number
  of neutrons in the nucleus
• Isotope An element that has a different mass
  than normal due to a change in the normal number
  of neutrons

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Electrons

• Located outside of the nucleus
• Unless otherwise indicated the number of
  electrons is the same as the number of protons
• Potential energy of electrons increases as their
  distance from the nucleus increases
• Electrons orbit the nucleus in energy levels

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Electron Energy Levels
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Electron Energy Levels

• The first energy level contains how many
  electrons?
• 2
• The second energy level contains how many
  electrons?
• 8
• The third energy level contains how many
  electrons?
• 8
• An element whose valence shell is complete is
  said to be what?
• Inert or unreactive

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Electron Orbitals
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Electron Configurations of First 18 Elements
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Chemical Bonds

• Covalent bond
• Sharing of a pair of valence electrons by two
  atoms
• Non-Polar Covalent bond
• Equal sharing of electrons
• Polar Covalent bond
• Unequal sharing of electrons

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• What sort of covalent bonds are seen here?

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Ionic Bonds

• Ion - transfer of electrons between atoms
• Ionic bond attraction between two oppositely
  charged ions
• Cation positively charged ion (lost electron)
• Anion negatively charged ion (gained electron)

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Hydrogen Bonds

• Oxygen is one of the most electronegative
  elements
• In a water molecule electronegative oxygen hogs
  electrons.
• This hogging of electrons results in which type
  of bond between oxygen and hydrogen within the
  water molecule?
• Polar covalent

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Hydrogen Bond

• Hydrogen bonds occur between two polar molecules,
  or between different polar regions of one large
  macro-molecule.
• One relatively negative region is attracted to
  a second relatively positive region.

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Van der Waals Interactions

• Weak attractions that occur when atoms and
  molecules are very close together
• May occur in regions of a single large molecule
  such as a protein

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Shape and function

• Molecular shape determines how molecules
  recognize and respond to one another
• Molecules with shapes similar to brain signal
  molecules can affect mood and pain perception
• Ex morphine and heroin mimic endorphins in the
  brain

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Chemical Reactions

• Starting materials are known as
• reactants
• Ending materials are known as
• products
• Matter can only be ______________ not created or
  ______________
• When forward and reverse reactions occur at the
  same rate, ______________ has been established

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Ionic bond, cation, anion