1. This is a step by step process! Creating Lewis/Structural formulas for molecules:

2. Identify the central atom - group priority is IV (4) – 1 st priority V (5) – 2 nd priority VI (6) – 3 rd priority Hydrogen and group VII atoms are never central atoms. If you have two of the same element that are the central atom, place them side by side and bond them first. Step 1

3. Step 2 Surround the central atom(s) with the other atoms.  The central atom is the one you selected as top priority.  If there is a tie (two of the same), you bond those to each other and then surround the bonded priority atoms (there are a few exceptions but we’ll ignore these for now.

4. Step 3 If group VI is involved as a central atom: Show as bent if there are only single bonds, meaning you may have to rewrite the final structure’s shape.

5. Step 4 To determine if the molecule has polar bonds: 1.Determine the types of atoms that are bonding. 2.Subtract their electronegativities. 3.Differences of:  0.40 or less — non-polar covalent  greater than 0.40 to 1.60 — polar covalent  greater than 1.6 — ionic

6. Step 5 To determine if a molecule is polar BOTH of these conditions must exist: - The molecule must have at least one polar bond. - The molecule must be asymmetric, meaning it looks lop-sided in some way.

7. Step 6 To determine van der Waals forces, you need to know there are 3 kinds: 1.London dispersion — more electrons, greater attraction. All molecules display this. This is the weakest force. 2.Dipole-dipole - attraction between the opposite poles of polar molecules. This is the next weakest force. 3.Hydrogen bond — similar to dipole-dipole, but must have hydrogen bonded directly to N, O or F. This is a fairly strong force of attraction.

8. Why do I need to know this stuff? The strongest van der Waals force determines physical properties so…

9. This means that:  Polar molecules including the ones that can hydrogen bond (strongest force) tend to be liquids and solids at room temperature. This is NOT always true but this does mean that they will have higher melting and boiling points than non-polar molecules of similar mass.  Polar molecules including the ones that can hydrogen bond tend to dissolve in each other. Sugar is polar, and so is water, so they mix well. Kerosene is non polar and does not mix with water because water is polar.