Question

What does a double bond represent? How many pairs of electrons are shared between the atoms in a double bond? Draw the Lewis structure of a simple molecule that contains a double bond.

Short answer

A double bond represents a chemical bond between two atoms where two pairs of electrons are shared, resulting in a strong connection and increased stability. In a double bond, there are two pairs of shared electrons, totaling four electrons involved in the bond. The Lewis structure of a simple molecule containing a double bond, such as O₂, is O=O, where each line (=) between the oxygen atoms represents a pair of shared electrons.

Step-by-step solution

Define a Double Bond

A double bond is a chemical bond between two atoms where two pairs of electrons are shared. This type of bond results in the strong connection of atoms within a molecule, making the molecule more stable and less reactive.

Number of Shared Electron Pairs

In a double bond, there are two pairs of shared electrons, which means a total of four electrons are involved in forming the bond between the two atoms.

Example: Lewis Structure of O₂

To provide an example of a simple molecule with a double bond, let us consider an oxygen (O₂) molecule. 1. Identify the number of valence electrons in each oxygen atom. In this case, oxygen has six valence electrons. Since there are two oxygen atoms, we have a total of 12 valence electrons available for O₂. 2. Draw the two oxygen atoms and place a bond between them, which represents two shared electrons (one electron pair). This leaves 10 valence electrons (12 initial valence electrons - 2 from the bond). 3. Add the remaining valence electrons around each oxygen atom to fill their outer shells, with each atom abiding by the octet rule (eight valence electrons per atom). In this case, after the initial bond, each oxygen atom gets four more electrons, totaling six valence electrons each. 4. To satisfy the octet rule, we need to share another pair of electrons between the two oxygen atoms. Remove two of the lone electrons on each oxygen atom and place them between the atoms as a second shared pair. This completes the double bond, with each oxygen atom having eight valence electrons (two pairs being shared and two lone pairs). The Lewis structure of a simple molecule containing a double bond, O₂, can be represented as: O = O where each line (=) between the oxygen atoms represents a pair of shared electrons.

Key concepts

Lewis Structure

In chemistry, a Lewis structure is a schematic representation of the valence electrons of atoms within a molecule, illustrating the specific bonding between atoms as well as the lone pairs of electrons that may exist. Valence electrons are shown as dots around the atomic symbols, and bonds between atoms are indicated by lines - a single line for a single bond and a double line for a double bond.

When drawing a Lewis structure, the first step is to calculate the total number of valence electrons that all atoms in the molecule have. This total will guide the placement of electrons to fulfill the octet rule for each atom. Once the valence electrons are placed as lone pairs, the remaining are used to form bonds between atoms. For molecules with double bonds, two pairs of electrons are shared, which is represented by two lines between the atoms. For example, in the Lewis structure of oxygen (O₂), a double bond is represented as O=O, with each oxygen sharing two pairs of electrons.

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom and are crucial in determining how an atom will chemically bond with others. These electrons have the most significant role in chemical reactions since they can be lost, gained, or shared to form bonds. For main group elements, the number of valence electrons corresponds to the atom's group number in the periodic table.

Understanding the configuration of an atom’s valence electrons is essential for predicting its chemical properties and behavior. In a Lewis structure, valence electrons determine how atoms bond. In the case of the oxygen molecule (O₂), each oxygen atom starts with six valence electrons. Therefore, to achieve a stable electron configuration, the atoms share electrons through a double bond.

Chemical Bonds

Chemical bonds are the attractive forces holding atoms together in molecules or compounds. There are various types of chemical bonds including ionic, covalent, and metallic bonds. A covalent bond, which includes single, double, and triple bonds, involves the sharing of electron pairs between atoms. The number of shared electrons determines the bond type: one pair for a single bond, two pairs for a double bond, and three pairs for a triple bond.

A double bond is a type of covalent bond where four valence electrons (two pairs) are shared between two atoms. This sharing results in a stronger and a shorter bond than a single bond, which only shares one pair of electrons. The double bond plays a significant role in the properties and structure of the molecule, as seen in the oxygen molecule's Lewis structure, where the double bond provides stability and a specific shape to the molecule.

Octet Rule

The octet rule is a chemical rule of thumb that states atoms tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The octet is energetically favorable and confers stability to the atom. There are exceptions to this rule, particularly for hydrogen (which follows the 'duet' rule, needing only two electrons) and for elements in periods beyond the second period of the periodic table that can have more than eight valence electrons.

In Lewis structures, the octet rule guides the placement of electrons to fulfill the atoms' need for eight valence electrons. Double bonds often form between atoms that can share two pairs of electrons to complete their octet, such as the two oxygen atoms in O₂. By sharing these electrons, both atoms achieve a full valence shell, satisfying the octet rule and creating a more stable molecule.