Unit 1.4

• Coordinate bonding is similar to covalent bonding. The only difference being that the shared pair of electrons come from the same atom.
• All bonding is a result of electrical attractions and repulsion between protons and electrons, with attractions outweighing repulsions. In covalent bonding, the electron pair between the 2 atoms repel one another but is overcome by the attractions to both nuclei.
• Electronegativity is the ability of an atom to attract a shared pair of electrons in a covalent bond.
• Polar bonds are created when the difference in electronegativity between the 2 atoms in a covalent bond is larger than 0.4 and 1.9. This means that the atom with a higher electronegativity will pull the shared pair of electrons closer to itself, becoming slightly negative, whereas the other less electronegative atom will become slightly positive as the pair of electrons are pulled away from it.
• If the electronegative difference between atoms in a covalent bond is larger than 2.0, the bond becomes ionic.
• VSEPR (valence she'll electron pair repulsion) states that lone pair-lone pair repulsion > lone pair-bonding pair repulsion> bond pair-bond pair repulsion.
• The shape of molecules can be predicted using VSEPR theory.
• Intermolecular forces are the forces of attraction the between molecules of a substance together
• Intramolecular bonding is the bonding between atoms of a molecule.
• Intermolecular forces are much weaker than intramolecular bonding.
• There are 3 types of intermolecular bonding: hydrogen bonding (the strongest), permanent dipoles and temporary dipoles (the weakest).
• Polar molecules have dipoles, one slightly negative end and one slightly positive end. These are permanent dipoles because of the difference in electronegativity. The slightly positive dipoles would be attracted to the slightly negative dipoles of another molecule, forming a temporary dipoles.
• Electrons are constantly moving around the nuclei in molecules. Therefore, at any given moment the electron cloud is unsymmetrical even in non-polar molecules. This causes temporary dipoles. The slightly positive temporary dipoles can attract the electrons of another molecule, inducing another temporary dipoles.
• Hydrogen bonds occur between molecules containing hydrogen atoms bonded to small, very electronegative elements which have lone pairs - fluorine, oxygen or nitrogen.
• A linear shaped molecule has 180° bond angles, 2 bond pairs and 0 lone pairs.
• A trigonal planar shaped molecule has 120° bond angles, 3 bond pairs and 0 lone pairs
• A tetrahedral shaped molecule has 109.5° bond angles, 4 bond pairs and 0 lone pairs.
• A trigonal pyramidal shaped molecule has 107° bond angles, 3 bond pairs and 1 lone pairs
• A bent shaped molecule has 104.5° bond angles, 2 bond pairs and 2 lone pairs.
• A trigonal bipyramidal shaped molecule has 120°/90° bond angles, 5 bond pairs and 0 lone pairs.
• An octahedral shaped molecule has 90° bond angles, 6 bond pairs and 0 lone pairs.