To determine the correct Lewis structure for ethylene (C2H4), we should follow the basic steps of drawing Lewis structures for molecules:
1. **Count the total number of valence electrons:** Each carbon atom has 4 valence electrons and each hydrogen atom has 1 valence electron. Thus, for C2H4, we have a total of:
$(2 \text{Carbon atoms} \times 4 \text{ electrons/Carbon}) + (4 \text{ Hydrogen atoms} \times 1 \text{ electron/Hydrogen}) = 8 + 4 = 12 \text{ valence electrons}.$
2. **Determine the central atom:** Hydrogen can only form one bond, so it cannot be a central atom. Therefore, the two carbon atoms must be central and bonded to each other.
3. **Sketch a skeleton structure:** Connect the central atoms with a single bond to begin with and arrange the hydrogen atoms around them.
4. **Distribute the remaining electrons to satisfy the octet rule:** Each carbon atom requires 8 electrons to fulfill the octet rule. Here is how you can distribute the electrons using the stepwise approach:
- Connect each hydrogen to a carbon with a single bond. Each bond is two electrons. This accounts for:
$(4 \text{ H-C bonds} \times 2 \text{ electrons/bond}) = 8 \text{ electrons}$
leaving us with:
$12 \text{ total valence electrons} - 8 \text{ electrons in H-C bonds} = 4 \text{ electrons}$
left to be placed.
- Place the remaining 4 electrons between the carbon atoms in the form of a double bond (two pairs of electrons), which satisfies the octet rule for both carbon atoms and uses up all 12 valence electrons.
5. **Review and confirm:** Each hydrogen atom has 2 electrons (full valence shell for hydrogen), and each carbon atom has 8 electrons, fulfilling the octet rule.
The correct Lewis structure is thus the one with each hydrogen single-bonded to a carbon and the two carbon atoms double-bonded to each other. In the list you provided, option C represents the correct Lewis structure for ethylene, C2H4:
```
H H
| |
H--C=C--H
| |
H H
```
Each line represents one pair of shared electrons (a single bond), and each pair of parallel lines between the carbon atoms represents two pairs of shared electrons (a double bond), fulfilling the octet rule for both carbon atoms and placing all hydrogen atoms with a full valence shell (two electrons).
