Lesson 4 | Polarity of Molecules

• Element is a pure substance made of all same atoms
• Compound - two or more elements bonded together
• group of atoms (2 or more atoms bonded together)
• not all molecules are compounds, but all compound are molecules
• CHEMICAL BONDING- attraction between atoms, ions or molecules that enables the formation of chemical compounds
• IONIC BOND – transfer of one or more valence electron (outer shell electron associated with an atom and that participates in the bonding process) from one atom to another ---- metal + non-metal
• COVALENT BOND – sharing an electron pair between atoms --- non-metal + non-metal
• Polar covalent – electrons are unequally shared, unbalanced distribution of electrical charge
• Non-polar covalent – equal sharing, balanced electron charge
• POLARITY means having dipoles or a positive and negative ends
• A dipole has 2 partially-charged regions / poles of a molecule and is symbolized by an arrowhead pointing to the more electronegative atom and a cross tail located at a less electronegative atom.
• POLAR COVALENT

  ▹ Have DIPOLES

  ▹ Polar bonds present and arranged in such a way that the bond dipoles do not cancel

  ▹ The charge is not uniformly distributed (electrically asymmetric)

  ▹ Have lone pairs (pair of valence electrons that do not participate in bonding) at the central atom
• NON-POLAR COVALENT

  ▹ Do not have dipoles because they add up to zero or cancel out

  ▹ The charge is uniformly distributed (electrically symmetric)

  ▹ No lone pairs on central atom
• OCTET RULE - attraction between atoms, ions or molecules that enables the formation of chemical compounds . An element should have contact to eight valence electrons in a bond or exactly fill up its valence shell, to ensure that the atom is stable.
• ELECTRONEGATIVITY DIFFERENCE (EN)

  -the degree to which an atom attracts electrons in a chemical bond

  Elements with the higher EN value become thepartial negative pole while elements with thelower EN value become the partial positive pole. This makes the molecule a polar molecule.
• ELECTRONEGATIVITY– tendency of an element to

  attract an electron from other atoms.
• MOLECULAR GEOMETRY

  -The valence shell electron pair repulsion theory or VSEPR theory helps predict the spatial arrangement of atoms in a polyatomic molecule.
• LEWIS DOT STRUCTURE - simplified representation of the valence shell electrons in a molecule. It is used to show how the electrons are arranged around individual atoms in a molecule. Electrons are shown as "dots" or for bonding electrons as a line between the two atoms.