Chapter 2 The Atomic Nature of Matter

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Chapter 2The Atomic Nature of Matter

• Department of Chemistry and Biochemistry
• Seton Hall University

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Atomic Theory

• Bulk of atomic theory was described by Dalton
• Basic key is the definition of a compound
  (anybody remember?)
• We can see individual atoms via STM, and it
  confirms our expectations (consider what if it
  didnt?)

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Daltons Theory

• All matter is composed of tiny particles called
  atoms
• All atoms of a given element have identical
  chemical properties that are characteristic of
  that element
• Atoms form chemical compounds by combining in
  whole-number ratios
• Atoms can change how they are combined, but they
  are neither created nor destroyed in chemical
  reactions (the Law of the Conservation of Mass)

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Several Related Points

• Matter and energy are interconverted, the amount
  of mass involved is unmeasureable
• Atoms and molecules are continually in motion
• Diffusion - the passage of a particle
• Dynamic equilibrium - balanced motion of
  particles (consider evaporation, diffusion)

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Atomic Architecture

• Matter is held together by forces
• gravitational
• electrical
• magnetic
• Atoms consist of
• nucleus - contains protons and neutrons
• electrons

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Atomic Architecture

• Nucleus contains essentially all of the mass of
  the atom, but essentially none of the volume
• Electrons have virtually none of the mass, but
  occupy basically all of the volume
• An atom the size of a baseball stadium will have
  a nucleus the size of a pea

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Atomic Diversity

• An element is identified by the charge of its
  nucleus (the number of protons)
• Isotopes have the same number of protons, but
  different number of neutrons
• X - element symbol
• A - atomic mass (number of protons and neutrons)
• Z - atomic number (number of protons)

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Isotopes

• Most elements occur naturally as two or more
  isotopes, hence the fractional atomic mass
• Isotopes of hydrogen
• protium - one proton, one electron
• deuterium - one proton, one neutron, one electron
• tritium - one proton, two neutrons, one electron
• Mass spectrometry - see fig 53 measures mass
  very precisely

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Charged species

• Charged chemical species are called ions
• cations - positively charged
• anions - negatively charged
• Ions can be atoms or molecules
• Compounds formed from two or more ions are called
  ionic compounds or salts
• Salts often dissolve in liquids to give separated
  ions

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Forms of energy

• Kinetic - E0.5mv2
• Potential
• Thermal
• Chemical
• Radiant
• Electrical

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Conservation of Energy

• Energy is neither created nor destroyed in a
  chemical process, but may be transferred from one
  body to another or changed from one form to
  another
• End of Chapter 2