Which molecule obey the octet rule?

Answer 1

Yes, it obeys the octet rule.

(Of coarse not an octet for the H atoms: they are saturated with a duplet (=2)).

To show you HOW this is done, you will need the structural formula:

If it is a monosaccharide there are already 32 different isomeres.

And even one of these and the most common one: alpha-D-gluco-pyranose (which is glucose) is too difficultto draw it in this simple 'html-text editor' layout.

Just as example some explaining calculation about electron bonding pairs and free pairs.

Valence electrons counting:

6 C = 6x4 = 24 e

12 H = 12x2 = 24 e

6 O = 6x6 = 36 e

Total of 84 electrons are available for free or covalent (= bonding) electron pairs

(total 84/2 = 42 pairs can be formed)

Needed for octets and H-duplets

6 C = 6x8 = 48 e

6 O = 6x8 = 48 e

12 H = 12x2 = 24 e

Total needed for octets/duplets = 120. These are 60 'needed to see' pairs

1. C has no free pairs, all 4 are covalent pairs (= 1 octet): 6x4 = 24 covalent bonds
2. O has 2 free and 2 covalent pairs (= 1 octet): 6x2 = 12 covalent bonds
3. H has no free pairs and 1 covalent pair (= 1 duplet): 12x1 = 12 covalent bonds

   Total of 24 double counted bonding pairs (48 pairs 'seen' from one atom AND 'seen' from the other atom bound to it, called covalent*) electron pairs)

One possible structure (which is not glucose) fitting the above calculation (1, 2, 3) is described here:

6 C atoms in a regular (bee hive) ring: 6 covalent pairs

6 H atoms directly to each C: 6 cov. pairs

6 O atom bonded at one side to each C atom: 6 cov. pairs

6 H atoms bonded to the other side of those 6 O atoms: 6 cov. pairs

Total of 24 double counted bonding pairs*) between all atoms.

This leaves 6x2 = 12 free electron pairs, two per O atom to fulfill their 'octet need'

And now you can conclude:

24 double counted = 48 'seen' electron pairs which are covalent*)

12 free electron pairs (2 on each O atom)

Total of 60 'structural drawn' pairs,

Thus this, being the same as the 'needed to see' pairs (60, see above), means that ALL atoms are obeying the octet(+ duplet) rule.

*) covalent means: 'seen by two' atoms which are bound together.

(The name of this formula would be 1,2,3,4,5,6-cyclo-hexane-hexa-ol, it isn't even a monosaccharide)

Answer 2

Most molecules will obey the octet rule. It does not matter how many shells the element has. An element with 3 shells is electrically stable with both 8 or 18 electrons in its valence shell.

Some molecules which obey this rule include oxygen and chlorine gas.

Answer 3

Molecules that do not follow the octet rule are usually more reactive than ones that do. Free radicals do not follow the octet rule. They have at least one unpaired electron.