How to determine the Lewis dot structure of O2
Oxygen atoms have 6 valence electrons. They need a stable octet but forming one bond wouldn’t help as this would leave them with only seven and one of these would be unpaired. However, forming a second bond would solve both these problems.
O2 has 6 + 6 = 12 valence electrons so you would think the O2 molecule would have O=O with two non bonded electron pairs on each O atom.
This is called singlet oxygen and does exist but not the normal structure for normal O2. The Lewis structure informs us that the molecule has a double bond that each of the oxygen atoms that make it up have two pairs of electrons without sharing.
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The form for normal oxygen is O – O with two non bonded electron pairs on each Oxygen atom and one unpaired electron on each O atom.
This is called triplet oxygen and is responsible for the pale blue color in liquid oxygen and the fact that liquid oxygen is paramagnetic.
The easiest way to them is in steps:
- Step 1: Count number of total Valance electrons (12 electrons in this case)
- Step 2: No. of Required electrons (always 8 hence, 16 electrons)
- Step 3: No. of Bonding Electrons (Required electrons – valence electrons: 4 electrons in this case)
- Step 4: No. of Non-Bonding Electrons (Valence electrons – Bonding electrons: 8 electrons)
The electrons in step 3 (4) tell you there will be a double bond and step 4 will tell you how many lone pairs of electrons are there (8) divide it by 2 and get the number of electrons per oxygen atom (8/2 = 4) hence 2 LONE pairs of electrons.
This works for any other atom/molecule/compound.
How to determine the Lewis dot structure of O2
Find the molecular formula. Oxygen gas = O2
Find how many total valence electrons in the substance. The oxygen atom has six, and there are two oxygen atoms, so your total is 12.
Arrange the atoms. In this case it’s easy: draw two Os, next to each other.
Make it a molecule- draw a line between the Os, representing a single bond. This bond contains one pair of shared electrons, leaving 10 more.
“Sprinkle” the rest of the electrons around the outer atoms, evenly in pairs, until you have placed all 10 remaining electrons.
Check the octet rule. Does each atom (besides hydrogen, but we don’t have any of those) have 8 electrons around it?
Remember the shared pair of electrons in the bond counts for both tons. You’ll see one of the oxygen atoms only has six, while the other one has 8.
So, what do you do when there aren’t enough of anything to go around? Share!
Take one pair of electrons from the oxygen atom with eight, and add another bond (shared pair) between the two atoms.
Now, you have a double bond. This allows both atoms to “have” the electrons in the bond, and both oxygen atoms now have 8 total electrons around them: four of their own, and four in the bond.
Done.
How to determine the Lewis dot structure of O2