U1L3 Intramolecular Bonds

Chemical Bonds

• Chemical bonds are formed between atoms by interaction of their respective electrons

• Three types of intermolecular bonds (bond that hold atoms in a molecule together

  • Ionic bonds

  • Covalent bonds

  • Polar covalent bonds

Ionic Bonds

• Ionic bond: occurs when there is a transfer of one or more electrons from one atom to another

• Transfer leads to the formation of a cation and anion

• Resulting electrostatic attraction between these two oppositely charged ions is an ionic bond

• Losing=positive, gaining=negative

• Opposite charges attract

Covalent Bonds

• Covalent bond: involves sharing of electrons between atoms to achieve a stable electron configuration (stable octet)

• Ex. 2 hydrogen atoms combine to form a molecule of hydrogen gas

• Electrons always attempt to move as far away from one another as possible creating different molecular shapes (VSEPR Theory)

• Like charges repel

• When there is an equal sharing of electrons, the bond is purely covalent

  • Same electronegativity and electron affinity, so same strength

  ---

Polar Covalent Bonds

• Polar covalent bond - occurs when there is an unequal sharing of electrons within a molecule

• Ex. in water, polar bonds are formed because O has a greater attraction for shared electrons (electronegative) than H

  • EN O = 3.5, EN H = 2.1

  • ΔEN = 3.5 - 2.1 = 1.4

• Polar bonds doesn’t always mean polar molecules

Determining Bond Type

• Type of bond that forms is determined by the difference in electronegativity of the 2 atoms involved

Determining Molecular Polarity

1. Draw a Lewis Dot Diagram for each atom

   

2. Determine structural formula of molecule

   

3. Does molecule have a positive end and a negative end?

• Symmetrical = non-polar

• Asymmetrical = polar

• Polar molecules are good solvents because they can disrupt ionic bonds

  ---

Polar Molecules are Good Solvents

• When salt and water are mixed, the negative end of water molecules are attracted to Na⁺, while the positive end of water molecules are attracted to Cl^-

• Water molecules form “spheres of hydration” around ions, causing the salt to dissolve