The Chemical Context of Life

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The Chemical Context of Life

• Atomic structure
• The periodic table
• Chemical bonding
• Important elements in living organisms

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A. Atomic Structure

• Matter
• Anything that takes up space and has mass
• Atom
• The smallest stable particle of matter
• Composed of protons, neutrons, and electrons

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A. Atomic Structure

• Protons
• Positively charged
• Atomic mass ? 1 atomic mass unit
• Located in the nucleus of an atom
• Neutrons
• Electrically neutral
• Atomic mass ? 1 atomic mass unit
• Located in the nucleus of an atom

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A. Atomic Structure

• Electrons
• Negatively charged
• Atomic mass very small, almost negligible
• Located in electron shells (orbitals) around the
  nucleus
• In a neutral atom, the number of electrons and
  protons is the same
• Atoms can lose or gain electrons during chemical
  bonding

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A. Atomic Structure

• Element
• A substance composed of only a single type of
  atom
• Atomic number of an element
• The number of protons in its atoms
• The atomic number is the same for all atoms of an
  element
• Mass number of an element
• The number of protons plus the number of neutrons
  in its atoms
• The atoms of an element may have a variable
  number of neutrons

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A. Atomic Structure

• Isotopes of an element
• Different forms of an element with the same
  atomic number but with different mass numbers
• The atoms of some isotopes are stable
• Other isotopes are radioactive, having unstable
  atoms that spontaneously break apart (decay) to
  form other atoms
• When radioactive atoms decay, energy is released

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A. Atomic Structure

• For example, carbon has three isotopes
• Carbon-12, with 6 protons and 6 neutrons, is the
  most common form of carbon
• Carbon-13, with 6 protons and 7 neutrons, is
  stable (non-radioactive) and rare
• Carbon-14, with 6 protons and 8 neutrons, is
  unstable (radioactive) and rare

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B. The Periodic Table

• In the periodic table
• Elements are listed in order of their atomic
  numbers
• Elements are designated by standard one or
  two-letter abbreviations
• Elements in the same vertical column often have
  very similar chemical bonding properties

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C. Chemical Bonding

• Chemical bonding occurs when two or more atoms
  combine
• Atoms combine by exchanging or sharing electrons
  in their outermost electron shell
• Chemical compound
• Formed when the atoms of two or more different
  elements combine by chemical bonding
• Properties of a compound are usually very
  different than those of its elements

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C. Chemical Bonding

• Ionic bonds
• Formed when electrons are completely transferred
  from one atom to another
• The atom that gains electrons becomes a negative
  ion (anion)
• The atom that loses electrons becomes a positive
  ion (cation)
• Example Sodium chloride Na Cl ? Na Cl

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C. Chemical Bonding

• Covalent bonds
• Form when two atoms share one or more pairs of
  electrons
• Molecule consists of two or more atoms that are
  joined by covalent bonding
• Covalent bonds are generally more stable than
  ionic bonds in aqueous (water) solution

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C. Chemical Bonding

• Other types of atomic molecular interactions
• Polar interactions
• Attraction between partially charged (polar)
  molecules and other polar or charged molecules
• Similar to ionic bonding
• Hydrogen bonding
• Interaction between a hydrogen atom and two
  strong electronegative groups
• Hydrophobic interactions
• Attraction between molecules that are insoluble
  in water

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D. Important Elements

• See table in the textbook
• Major covalent constituents of biomoleculesC H
  N O P S