CHEMISTRY 2 3RD QUARTER

• Atoms are the building blocks of matter, the shape of an atom explain elements behavior
• Atomos (400 BC)


  • Democritus
  • Atoms are the building blocks of matter, the shape of an atom explain elements behavior
• Solid Sphere (1803)


  • John Dalton
  • Atom is a solid indivisible sphere
• Plum Pudding (1897)


  • J.J Thomson
  • Negative electrons are embedded in a sea of positive charges
• Nuclear (1911)

  • Ernest Rutherford
  • Positive charges are located within a central nucleus
• Planetary (1913)

  • Niels Bohr
  • Electrons are restricted in circular orbits with different energy levels
• Quantum (1926)

  • Erwin Schrödinger
  • Electrons are in clouds surrounding the nucleus, and this cloud is less dense
• Atomic Orbitals


  • Electrons act like waves
  • The exact location of electrons cannot be determined
• Orbitals


  A region in an atom where there is a high probability of finding electrons
• Atomic Orbitals


  • s
  • p
  • d
  • f
• Quantum Numbers

  • Principal (Distance of the electron from nucleus)
  • Azimuthal (Shape of the orbital)
  • Magnetic (Orientation of the orbital)
  • Spin (Orientation of the electron spin)
• Electron Configuration Notation


  Describes how electrons are distributed in atomic orbitals
• Stability of Noble Gases

  • Elements in Group 8A also called as noble gases are the most stable elements in the periodic table and are thus nonreactive under ordinary conditions
  • Except for helium with only two electrons in its orbital, noble gases have 8 valence electrons
  • Such octet configuration is the most stable arrangement an atom can have
  • The atoms of the other elements in the periodic table tend to achieve the configuration of the nearest noble gas by reacting with the same element or with other elements to form new compounds
  • This principle is referred to as the octet rule
• Lewis Structure


  A system of representing the valence electrons of atoms using diagrams

  
• Writing Lewis Structure

  1. Place a dot in each of the four sides of the element symbol before pairing with another as needed to represent all the valence electrons

  2. There are no strict rules on which sides to pair up first
• Ions and their Lewis Structure

  • Metals have one to three valence electrons, which can be easily removed because of their relatively low ionization energy
  • Nonmetals having high electron affinity, can gain valence electrons to fill their s and p orbitals and form an octet

  
• Group Number and Valence Configuration of a Neutral Atom


  Related to the charge of its corresponding ion
• Formation of Ionic Compounds

  Electrons given off by a metal atom are gained by the nonmetal, forming ionic bond in the process
• Ionic Compounds and Lewis Structure

  Ionic compounds generally exist between a metal and a nonmetal as a result of their high electronegativity difference
• Properties of Ionic Compounds

  • High melting point and boiling point (Strong ionic bonds require high energy to separate)
  • Conduct electricity in solution (Ions can move freely)
  • Some can conduct electricity in solid state (Solid electrolytes)
  • Solid at room temperature (Stable lattice structure)
  • Hard and brittle (Fixed and stable lattice)
• Covalent Bonding


  • Nonmetal atoms have relatively similar electronegativities, they tend to attract valence electrons equally (or almost equally) and just share them to achieve an octet (or duet)
  • Compounds that result from covalent bonding are called molecular compounds
• Types of Covalent Bond

  • Single covalent bond
  • Double covalent bond
  • Triple covalent bond
• Drawing Lewis Structure of Molecules and Polyatomic Ions

  1. Find the number of electrons available for distribution

  2. Arrange the atoms, the least electronegative atom is assigned as the central atom

  3. Distribute the remaining electrons such that there are two electrons for hydrogen and eight electrons for other atoms

  4. If there are not enough electrons for the atoms to have eight electrons each, change the single bonds to double or triple bonds

  5. If there is more than one Lewis structure, choose the symmetrical one

  6. Enclose the structure of a polyatomic ion in brackets and place the charge at the upper right corner

  
• Formal Charge


  • Compares the number of electrons "owned" by an atom in a molecule or ion with those possessed by the atom in a free state
  • Formal charge = (no. of valence electrons) - (no. of unshared electrons) - (1/2 no. of shared electrons)

  
• Formal charges help determine the correct Lewis structure of a molecule or polyatomic ion

  
• Electronegativity


  The ability of an atom in a molecule to attract shared electrons towards itself
• Atoms with higher electronegativity attract the shared electrons towards themselves greater than others
• Uneven charge distribution


  Some sites in a molecule or ion are electron-rich, electron-poor, or neutral

  
• Formal charge


  Compares the number of electrons "owned" by an atom in a molecule or ion with those possessed by the atom in a free state

  
• Formula for finding formal charge

  Formal charge = (no. of valence e-) - (no. of unshared e-) - (1/2 no. of shared e-)

  
• Carbon dioxide (CO2)


  • Formal charges of each atom

  
• Carbonate ion (CO3^2-)


  • Lewis structure and formal charges of each atom

  
• Molecular Geometry


  • The 3-dimensional arrangement of atoms within a molecule or polyatomic ion

  
• VSEPR Theory


  Electron pairs around an atom assume an arrangement in space that reduces the repulsions between them
• Arrangement of electron domains

  1. Two domains - 180°

  2. Three domains - 120°

  3. Four domains - 109.5°
• Polarity


  Separation of electric charges leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end
• Polar molecules


  • Must contain polar bonds due to a difference in electronegativity between the bonded atoms
• Nonpolar covalent bond


  Bonding electrons shared equally between two atoms, no charges on atoms
• Polar covalent bond


  Bonding electrons shared unequally between two atoms, partial charges on atoms
• Ionic bond


  Complete transfer of one or more valence electrons, full charges on resulting ions