Double bond

Tiny bits called atoms hold hands to make things.

Most bits hold hands just once. This is a single bond. But some bits hold hands twice. This is a double bond.

A double bond uses four tiny parts to stay together. This makes the grip very strong. It also makes the bond short.

Carbon atoms often hold hands this way. They can also hold hands with oxygen. These bonds help build many things.

Scientists draw these bonds with two lines. It looks like an equals sign. It shows a very tight grip.

Atoms use bonds to stick together. Most atoms use a single bond. This uses two electrons. A double bond is different. It uses four electrons to hold atoms together.

Double bonds are very strong. They are also shorter than single bonds. Carbon atoms often form these bonds. This happens in things called alkenes. Carbon can also bond with oxygen. This is called a carbonyl group. Other atoms like nitrogen and sulfur can do this too.

Scientists draw a double bond with two lines. It looks like an equals sign. This was first used by Alexander Butlerov.

In a molecule like ethylene, the bond is made of two parts. One part is a sigma bond. The other part is a pi bond. The pi bond makes it hard for atoms to turn. They must stay in place. This can lead to different shapes in a molecule. Some molecules have bonds that skip along a chain. This is called conjugation.

In some heavy elements, double bonds act differently. They may not be flat. They can even twist or bend. This is true for elements like tin or lead.

Atoms use bonds to stick together. A double bond is a special kind of connection. It is a covalent bond between two atoms. This bond uses four bonding electrons. A single bond only uses two electrons. Double bonds are very important in chemistry. They are often found between two carbon atoms. These are called alkenes.

How does a double bond work? It is actually made of two different parts. First, two orbitals overlap to form a sigma bond. This is the first connection between the atoms. Next, two p-orbitals come together to form a pi bond. For this to work, the p-orbitals must stay parallel. This means the atoms cannot rotate around the bond. Because they cannot turn, molecules can have different shapes. This is called cis-trans isomerism.

Scientists have studied these bonds for a long time. A Russian chemist named Alexander Butlerov introduced them. He created the way we write them in chemical notation. In a skeletal formula, we draw them with two parallel lines. This looks just like an equals sign. This simple drawing helps scientists see how atoms connect.

Double bonds have very specific measurements. They are shorter and stronger than single bonds. For example, an ethylene C=C bond is 133 pm long. A single C-C bond in ethane is 154 pm. The energy for a double bond is 636 kJ mol-1. A single bond is only 368 kJ mol-1. These bonds are also electron-rich. This makes them reactive with things like halogens.

Double bonds appear in many different places. You can find them between carbon and oxygen. This is called a carbonyl group. They also exist in azo compounds with nitrogen. Some bonds can even skip along a chain. This is called a conjugated system. In heavy elements like tin or lead, they act differently. These bonds might twist or bend instead of staying flat.

In chemistry, a double bond is a specific type of covalent bond. A covalent bond happens when two atoms share electrons to stay connected. While a single bond involves only two bonding electrons, a double bond involves four electrons. This extra sharing changes how the atoms interact. Double bonds are vital to the structure of many molecules. They are often found between two carbon atoms in molecules called alkenes.

To understand how a double bond works, we must look at orbital hybridization. This describes how an atom's electron clouds, or orbitals, change shape to bond. In a molecule like ethylene, each carbon atom has three sp2 orbitals. These three orbitals lie flat in a single plane with angles of about 120 degrees. The fourth orbital is a p-orbital, which sits perpendicular to that plane. When the two carbon atoms approach, two sp2 orbitals overlap to create a sigma bond. This is the primary connection between the atoms. At the same time, the two p-orbitals overlap to form a pi bond.

The pi bond created by the p-orbitals has very specific rules. For the overlap to be at its maximum, the p-orbitals must remain parallel to each other. Because they are locked in this parallel position, the atoms cannot rotate around the central bond. This lack of rotation leads to a phenomenon called cis-trans isomerism. This means molecules can have different shapes based on how their parts are arranged. This structural rigidity is a direct result of the pi bond's geometry. This property is essential for understanding how complex molecules behave.

Double bonds are physically different from single bonds in several ways. They are generally shorter and much stronger. For instance, the carbon-to-carbon bond in ethylene is 133 pm long. In contrast, the single bond in ethane is 154 pm. The strength, or bond enthalpy, is also much higher. An ethylene double bond has a strength of 636 kJ mol−1. A single bond in ethane is only 368 kJ mol−1. However, the double bond is not exactly twice as strong as a single bond. This is because the pi bond is weaker than the sigma bond due to less effective overlap.

Chemists use specific notation to represent these connections in formulas. The Russian chemist Alexander Butlerov introduced double bonds into chemical notation. In a skeletal formula, a double bond is drawn as two parallel lines. This looks exactly like an equals sign. Double bonds are also electron-rich areas. This high density of electrons makes them reactive. They can easily participate in addition reactions, such as those involving halogens. These reactions occur because the bond is looking for electron acceptors.

Double bonds appear in many different chemical groups. You can find them in carbonyl groups, which connect carbon to oxygen. They also exist in imines, where carbon connects to nitrogen. Azo compounds feature a nitrogen-to-nitrogen double bond. In some molecules, double bonds can alternate with single bonds in a chain. This creates a conjugated system, where p-orbital overlap extends over many atoms. This can even lead to aromaticity in cyclic molecules. However, in cumulenes, two double bonds sit next to each other without overlapping.

There is a concept known as the double bond rule. This rule notes that double bonds are common among period 2 elements like carbon, nitrogen, and oxygen. They are much less common with elements from higher periods. Heavier elements in group 14, like tin and lead, behave differently. Their double bonds often create twisted or bent structures rather than flat ones. For example, distannenes have a trans bent structure. In these heavy elements, the bonding often involves weak donor-acceptor interactions rather than strong shared overlaps.