Question

How many electrons are involved when two atoms in a molecule are connected by a "double bond"? Write the Lewis structure of a molecule containing a double bond.

Short answer

In a double bond, four electrons are involved as two pairs of electrons are shared between two atoms. The Lewis structure for an oxygen molecule (O2) containing a double bond is \( \mathrm{O} = \mathrm{O} \), where each oxygen atom has two bond pairs (the double bond) and two lone pairs.

Step-by-step solution

Understand the concept of a double bond

In a double bond, two pairs of electrons are shared between two atoms. This means that a total of four electrons are involved in a double bond.

Write the Lewis structure for a molecule with a double bond

To write the Lewis structure of a molecule containing a double bond, follow these steps: 1. Determine the total number of valence electrons in the molecule. 2. Choose a central atom, which is usually the element that needs the greatest number of electrons to complete its octet (except Hydrogen). 3. Place the remaining atoms around the central atom. 4. Add single bonds between the central atom and each surrounding atom. 5. Distribute the remaining valence electrons as lone pairs to complete the octet of each atom (except hydrogen, which needs only a pair). 6. If any atoms still lack a complete octet, move the lone pairs to form a double bond (creating a shared pair of electrons). As an example, let's draw the Lewis structure for a molecule of oxygen (O2).

Determine total valence electrons

Each oxygen atom has 6 valence electrons. So, in the case of O2, there is a total of 12 valence electrons (6+6).

Choose the central atom

Since there are only two oxygen atoms in O2, they will both be central atoms.

Place surrounding atoms

As there are only two atoms, they will be bonded together.

Add single bonds between atoms

Draw a single bond between the two oxygen atoms. This will use 2 of the 12 valence electrons.

Distribute remaining valence electrons

Each oxygen atom needs 6 more electrons to complete its octet. Distribute the remaining electrons as lone pairs. There are two pairs of electrons for each oxygen atom currently and 10 more valence electrons to be distributed \$ (12 - 2 = 10) \$.

Move lone pairs to form a double bond if needed

Since the octet for each oxygen atom has not been completed, we move two lone pairs on each oxygen atom to be shared between them, creating a double bond (two shared pairs). Now, we have a double bond between the two oxygen atoms, and each oxygen atom has a completed octet. The final Lewis structure for the oxygen molecule containing a double bond is: \[ \mathrm{O} = \mathrm{O} \] Each oxygen atom has two bond pairs (represented by the double bond) and two lone pairs.