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Valence electrons are the outermost electrons of an atom and are crucial in determining how the atom will interact with others. These electrons can participate in forming chemical bonds with other atoms, as they are the ones most loosely held by the nucleus. In the context of ethylene ((C_{2}H_{4})), each carbon atom contributes four valence electrons and each hydrogen atom contributes one.

By adding up the valence electrons from all the atoms in ethylene, we come to a total of 12 valence electrons that are available for bonding. Understanding the count of valence electrons is the first step in predicting the chemical properties and bond patterns of a molecule, which eventually lead to the creation of its Lewis structure.

Chemical bonding is the force that holds atoms together in a molecule. There are primarily three types of chemical bonds: ionic, covalent, and metallic. Ethylene, a simple hydrocarbon, is an example of a molecule that forms covalent bonds, which involve the sharing of pairs of valence electrons between atoms.

In the Lewis structure for ethylene, each hydrogen atom shares its single electron with a carbon atom, forming four simple covalent bonds. Moreover, the carbon atoms share a pair of electrons forming a single bond, and they also share another pair to fulfill the carbon atoms' need for more electrons, resulting in a double bond C=C. Through these shared pairs, or bonding pairs, all atoms achieve greater stability resembling noble gas configurations.

The octet rule is a chemical rule of thumb that reflects the observation that atoms tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electron configuration as a noble gas.

The exception to this rule is hydrogen, which can reach a stable configuration with only two electrons. For the carbon atoms in ethylene, forming four single covalent bonds does not suffice to complete each carbon's octet. By forming a double bond, where two pairs of electrons are shared, each carbon ends up surrounded by an octet of electrons, adhering to the octet rule. This is reflected in the final Lewis structure of ethylene, (H_{2}C=CH_{2}), where each line between the atoms represents a pair of shared electrons.