Atomic Structure

• ATOM


  basic unit of an element
• NUCLEUS


  positive charge
• ELECTRON


  negative charge
• PROTON


  positive charge
• NEUTRON: a subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen.
• ATOMIC NUMBER


  number of protons in the nucleus
• RELATIVE ATOMIC MASS

  6.203 X 10^23
• Material Science Technology Programme (AS270), Faculty of Applied Sciences, UiTM Shah Alam
• Atom


  Basic Unit of an Element
• Atom


  • Diameter: 10 –10 m
  • Neutrally Charged
• Parts of an Atom


  • Nucleus
  • Electron Cloud

  
• Nucleus


  • Diameter: 10 –14 m
  • Accounts for almost all mass
  • Positive Charge

  
• Electron Cloud


  • Mass: 9.109 x 10 –28 g
  • Charge: -1.602 x 10 –9 C
  • Accounts for all volume
• Proton


  • Mass: 1.673 x 10 –24 g
  • Charge: 1.602 x 10 –19 C
• Neutron


  • Mass: 1.675 x 10 –24 g
  • Neutral Charge
• Atomic Number


  Number of Protons in the nucleus
• Relative atomic mass


  Mass in grams of 6.203 x 1023 (Avagadro Number) Atoms
• One Atomic Mass unit is 1/12th of mass of carbon atom
• One gram mole


  Gram atomic mass of an element
• Atomic number (proton number) plus neutron number equals mass number


  • Z+N=A
  • Neutron excess: D = N - Z = A - 2Z
• Electronic Configuration


  Arrangement of electrons in an atom
• Rules for Electronic Configuration


  • Aufbau principle
  • Pauli Exclusion principle
  • Hund's rule
• Electronegativity


  Ability of an atom in a molecule to attract the bonding electrons to itself
• Factors affecting Electronegativity
• Ionic bonds


  Strong atomic bonds due to transfer of electrons
• Covalent bonds


  Large interactive force due to sharing of electrons
• Electronegativity


  • Increases as we move across a period
  • Decreases descending (move down) a group
• Factors affecting electronegativity


  • Atomic size
  • Effective nuclear charge
• Small atom with high effective nuclear charge


  Has a greater ability to attract the bonding electrons to itself
• Electronegative elements


  Accept electrons during chemical reaction
• Some elements


  Behave as both electronegative and electropositive
• Electronegativity


  • The degree to which the atom attracts electrons to itself
  • Measured on a scale of 0 to 4.1
  • Example: Fluorine is 4.1, Sodium is 1.0
• Types of atomic and molecular bonds


  • Ionic bonds
  • Covalent bonds
  • Metallic bonds
  • Permanent Dipole bonds
  • Fluctuating Dipole bonds
• Ionic bonding


  Strong atomic bonds due to transfer of electrons
• Covalent bonding


  Large interactive force due to sharing of electrons
• Metallic bonds


  Non-directional bonds formed by sharing of electrons
• Permanent Dipole bonds


  Weak intermolecular bonds due to attraction between the ends of permanent dipoles
• Fluctuating Dipole bonds


  Very weak electric dipole bonds due to asymmetric distribution of electron densities
• Ionic bonding


  1. Electropositive element

  2. Electronegative atom

  3. Electron transfer

  4. Cation (+ve charge)

  5. Anion (-ve charge)

  6. Electrostatic attraction
• Ionic bonding in NaCl


  • Sodium atom
  • Chlorine atom
  • Sodium ion (Na+)
  • Chlorine ion (Cl-)