They can bond by holding hands or interlocking their arms. Once they've formed their molecule, have them move around again like before by telling them that the temperature has gotten warmer, like the temperature of the room they are in. If there is an odd number of people, one group can have third person bond with them. Some may say that it's harder because they had to stick with their buddy, while others may say that it was about the same. Depending on time, you can also have them find out what number they have bonded to.
Many molecules form by identical atoms bonding together, like oxygen and nitrogen molecules.
The oxygen molecules they breathe are each made of two oxygen atoms that have bonded together. The same is true for nitrogen, except that two nitrogen atoms are bonded together. Molecules form this way, also. Two examples are carbon monoxide and nitrogen monoxide, in which either a carbon or a nitrogen atom binds with an oxygen atom. Both molecules are bad for us and are considered air pollutants.