Bonding and Shapes of Molecules

• Atoms are electrically neutral because they have equal numbers of protons and electrons
• An ion is a charged atom
• Cation is positive
• Anion is negative
• Atoms complete incomplete outer shells by gaining/losing electrons to become stable
• Hydroxide ion, OH-
• Sulfate ion, SO4(2-)
• Nitrate ion, NO3-
• Carbonate ion, CO3(2-)
• Ammonium ion, NH4+
• Ionic bonding is between metals and non-metals
• Isoelectronic: When two atoms have the same number of electrons
• The bond is due to electrostatic attraction between oppositely charged ions
• Noble gases have full valance shells, making them stable
• In an ionic compound, millions of ions compact to form a 3D structure called a giant lattice
• Properties of a giant lattice:

  • High MP, BP because of high energy needed to break the electrostatic bonds
  • Can't conduct electricity normally because they're too corrupt
  • Dissolves; can conduct electricity in water because electrons get free space
  • Crystaline structure
• If energy valor is released by water binds to ions if the greater than the energy needed to overcome the bond, the substance dissolves
• Ionic compounds are brittle, when they get hit, the rows slide and places the same charges on top of each other, the charges repel and the lattice splits and shatters
• Non-metals bond via sharing valance shell electrons to form a covalent bond
• Non-metals attain a full valance via bonding
• A single covalent bond is an electrostatic attraction between a pair of shared valance electrons and the nuclei of the atom
• Covalent bonds are extremely strong but the strength varies on the atoms involved
• The protons of an hydrogen atom are held together by the electrostatic attraction to the shared pair of electrons
• In dot and cross diagrams, only valance shell are necessary to be depicted
• A lone pair of electrons are a pair of electrons in the outer shell that are not part of a covalent bond
• A dative (co-ordinate) bond occurs when an atom shares a lone pair of electrons to form a bond
• Covalent Properties:

  • Weak forces between molecules
  • Low MP and BP
  • Good insulator (neutral molecules, no free charge carriers)
  • Soluble in non-polar solvent
  • Do not conduct (no mobile charged particles)
• Polar Molecules:

  • May dissolve in polar solvents
  • Solubility depends on strength
  • Molecules can have polar or non-polar parts
• Non-polar molecules:

  • Simple molecules usually soluble
  • Non-polar molecules will form intermolecular forces
  • Non-polar molecules are usually insoluble in polar solvents
• Charge Density: The amount of charge in a given area
• Across a period, the radius decreases and the charge density increases
• Down a group, the radius increases and the density decreases
• Charge density applies to ionic radii only, not atomic radii
• VSEPR: Valance Shell Electron Pair Repulsion
• VSEPR:

  • Electrons repel each other and arrange themselves far apart from each other as possible
  • Electron pairs surrounding a central atom therefore determine the shape of a molecules or ion
  • Different numbers of Electrons around an atom result in different shapes
• Repulsion Hierarchy:

  bonded-bonded < bonded-lone < lone-lone
• Lone pairs are more repulsive because they take up less volume with the same charge; thus having a bigger charge density
• A solid line represents the bond
• A solid wedge represents the bond coming out
• A dotted line represents the bond going behind