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While covalent bonds are relatively strong, the intermolecular forces between molecules are weaker. To contrast, the lattice energy must be overcome to separate the ions from each other in ionic compounds.

Think of this section as an introduction. It is much easier to write electron-dot structures using the rules listed in the next section.

We have single, double, and triple bonds.

The rules seem arbitrary to students.

They have been developed in order to get to a finished structure.

It’s important to follow the rules as developed. Otherwise, students have a difficult time knowing when to do multiple bonding.

Step 2: The positioning of the terminal atoms about the central is not critical as long as they simply surround the central atom.

Step 3: The terminal atom is hydrogen.

Step 5: The central atom has an octet so no multiple bonding.

Step 4: The central atom already has an octet.

Step 5: The central atom has an octet so no multiple bonding.

Step 1: Subtract 1 from the total number of valence because of the 1+ charge.

Step 3: The terminal atoms are hydrogen.

Step 5: The central atom has an octet so no multiple bonding.

Don’t forget to show the charge on the ion!

Step 2: The least electronegative atom is the central one (hydrogen can’t be the central atom).

Step 3: Two of the terminal atoms are hydrogen.

Step 4: There are no remaining electrons to place on the central atom.

Step 5: “Borrow” a pair from oxygen to complete the central atom’s octet.

Step 2: The central atom is in row 3 so there can be more than 8 electrons.

Step 4: There are no remaining electrons.

Step 5: The central atom has at least 8 electrons so no multiple bonding.

Step 4: The remaining electrons go on the central atom.

Step 5: The central atom has at least 8 electrons so no multiple bonding.

Step 4: There is only 1 more pair of electrons. Thus, the central oxygen only has 3 pairs of electrons (less than an octet). Step 5: There is a choice to be made. If all that is desired is the electron-dot structure, then either of the 2 terminal oxygen atoms could have been chosen.

Either electron-dot structure suggests that ozone has a double and a single bond. A bond analysis actually shows one type of bond and it’s neither a single nor a double bond. A resonance hybrid attempts to overcome this shortcoming of electron-dot structures. At this stage, we usually just take this simplified look at resonance structures. Organic chemistry, for example, takes a much deeper look at resonance.

The sum of the formal charges will be equal to the overall charge of the molecule or ion.

How can carbon have 4 bonds if there are only 2 unpaired valence electrons?

Promotion of 1 electron allows for 4 unpaired valence electrons.

The 4 bonds in CH4 must be equivalent (tetrahedral distribution).

Summary.

Pictures of liquid oxygen attracted to the poles of an electromagnet are nice to show at this point.