The Chemical Foundations of Life

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Chapter 2
The Chemical Foundations of Life
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Key Questions

• What is matter?
• What determines the properties of an atom?
• What kinds of bonds bring atoms together to form
  molecules?
• What special characteristics of water made it
  possible for life to evolve?

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What is Matter?

• Matter is any substance that
• Occupies space
• Has mass
• Exists in different states or phases
• Solid
• Liquid
• Gas
• Matter consists of one or more pure substance
• Element has its own unique properties
• Chemical rxns transform pure substances into
  other substances, w/o changing the total amount
  of matter
• Chemical rxns cannot change or destroy elements

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Elements, Atoms Molecules

• Elements pure substances that cannot be
  converted into simpler substances in chemical
  reactions
• Ex H, He, O, C, Ag, Au.
• 92 naturally occurring elements
• Elements can be created or changed by means of
  nuclear rxns,
• Nuclear rxns the high-energy transformation of
  individual atoms that occur in a nuclear reactor
  or in the core of stars such as sun
• Atoms tiny particles that compose elements
• The smallest units that still have properties of
  an element
• Atoms are made of smaller subatomic particles,
  including protons, neutrons, and electrons
• Molecules stable assembly of 2 or more atoms
• Ex H2, O2, N2.

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Periodic Table of Elements
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Common Elements Found in Living Organisms

• Carbon 18
• Oxygen 65
• Hydrogen 10
• Nitrogen 3
• Others 4

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Distribution of Elements in the Human Body and
the Earths Crust
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Compounds and Mixtures

• Compounds pure substances formed from 2 or more
  different elements
• Water, H2O
• Carbon Dioxide, CO2
• A compound is unlike the elements that compose it
• Mixture Random combinations of compounds
• Ex sand and salt
• The sand remains sand and the salt remains as
  salt
• One component of a mixture does not affect the
  properties of the other components
• The components of a mixture can be present in any
  ratio
• Sugar and milk in coffee

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What Is an Atoms Structure?

• Atom is made of
• Protons positive charge, located in nucleus,
  heavy
• Neutrons neutral charge, located in nucleus,
  heavy
• Electrons negative charge, located in shells
• Atomic number equals the number of protons.
• Atomic weight equals the number of protons and
  neutrons.
• Usually an atom is neutral, so the number of
  protons equals the number of electrons.

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Decaying Atoms and Isotopes
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Chemical Bonds

• Covalent Bonds 2 atoms share one or more
  electrons
• Strongest most common one in living organisms
• Sometimes unequal sharing polar
• Examples water, methane

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Chemical Bonds

• Ionic bonds atoms gain or lose electrons
• Form a positive or negative ion
• Example NaCl
• Electronegativity the atoms of each element have
  the tendency to attract electrons

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Water The Most Important Life Molecule

• Special properties of water
• Density liquid phase is more dense
• Heat Capacity absorbs large amounts of heat

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More Water Properties

• Cohesion ??? an attraction between molecules of
  the same substance
• stickiness of water
• Surface tension the tendency of a substance to
  form a smooth round surface
• Water is high cohesive and create high surface
  tension
• Water is cohesive because of H-bond
• Adhesion ???A substance clings to and wets
  other surfaces
• Waters adhesiveness results from the tendency of
  water molecules to form H-bond w/ other polar or
  charged molecule
• Capillary action Water clings to itself
  (cohesion) and clings to other surfaces
  (adhesion), makes it readily enters and climbs
  tiny tubes
• Waters cohesiveness and adhesiveness help trees
  raise water from roots deep in the ground to
  leaves hundreds of feet in the air
• Solvent ability to dissolve

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More Water Properties

• Solvent A solvent is any fluid in which other
  substance dissolve
• Ex. Salt in water
• Water is a powerful solvent, especially for ions
  (ex. Salt) and polar molecules (ex. Sugar)
• The water molecules crowding around the ions
  separate them from one another
• Some molecules are amphipathic have both
  hydrophobic and hydrophilic regions
• Detergent, remove oil by making it soluble in
  water
• Phospholipid, a membrane component with
  hydrophilic heads point outward and hydrophobic
  tails pointing inward

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How Do Water Molecules Change in Solution?

• Hydrogen ion When hydrogen atom has no electron
  at all and becomes a naked nucleus, it is just a
  proton, can jump back and forth between the
  oxygen atoms of two different water molecules
• Water Molecules Swap Protons
• Hydroxide ion Water loses a proton, has a
  negative charge
• Hydronium ion Water w/ an extra hydrogen ion
  (H), has a positive charge
• Ions form due to the unequal sharing of electrons

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Acids, Bases pH

• Acid - molecule that can give up a hydrogen ion
• An acid dissolved in water adds H to the water
  and raises the concentration of H
• Ex. Vinegar, stomach acid
• Base a molecule that can accept a H
• pH scale that measures the number of hydrogen
  ions ie. power of hydrogen
• pH scale is based on the logarithm of the
  concentration of H
• The greater the conc. of hydrogen ions, the lower
  the pH value
• Ex. Stomach acid pH 1, saliva pH 7
• Human blood pH 7.4,
• pH lt 6.95 nervous system unresponsive then coma
  and death
• pH gt 7.7 nervous system overreactive then muscle
  spasms and convulsion
• Acid blood from severe diarrhea
• Basic blood from diuretic or took too much HCO3-
  of soda for an upset stomach

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Key Concepts

• Atom fundamental unit of an element
• Molecule fundamental unit of a compound
• Covalent bonds involve a sharing of electrons
  unequal sharing results in a polar molecule
• In an ionic bond, electrical attraction holds
  atoms together
• Molecules interact by forming hydrogen bonds or
  hydrophobic interactions