Chemical bond

A chemical bond is the connection that holds together atoms or ions to form molecules, crystals, and other structures. This bond can happen in different ways.

One way is through the force between oppositely charged ions, called an ionic bond. Another way is when atoms share electrons, known as a covalent bond. There are also weaker connections, like hydrogen bonds, that help shape the structure of many important molecules.

Because opposite electric charges attract, the negatively charged electrons around an atom’s center, called the nucleus, are pulled toward the positively charged protons inside the nucleus. When electrons are shared between two nuclei, they are pulled toward both, holding the atoms together. This sharing creates a stable distance between the nuclei.

Chemical bonds are very important because they decide how atoms are arranged and what properties different materials have. Whether we are looking at the soft, shiny metal of a metal or the exact shape of a small molecule, these bonds are what make each substance unique. Scientists use special theories, like quantum theory, to understand and predict how strong and what kind of bonds will form in different situations.

Overview of main types of chemical bonds

A chemical bond is when atoms stick together. This happens because of how the outer parts of atoms, called valence electrons, behave. There are a few main types of bonds.

One common type is a covalent bond, where atoms share electrons. This sharing makes the atoms stick together in certain shapes, like how molecules form. Covalent bonds can make things soft, like waxes, or very strong, like diamonds.

Another type is an ionic bond, where one atom gives an electron to another atom. This creates positively and negatively charged particles that stick together because of their opposite charges. Ionic bonds make things like table salt, which are strong but can break easily.

Metallic bonding is another type, where atoms in metals share their electrons in a “sea” that moves freely. This makes metals strong but also easy to bend, and it helps them conduct electricity and heat well.

History

Main articles: History of chemistry and History of molecular theory

Pre-atomic chemical theory

In the late 1600s, Robert Boyle said that elements are different from compounds. Later, Antoine Lavoisier showed that compounds are made of elements in fixed amounts. He showed that water can be split into hydrogen and oxygen. He also said that in chemical reactions, matter does not disappear—it just changes form.

Atomic theory

Main article: History of atomic theory

In 1911, Ernest Rutherford found that atoms have a tiny, dense center called a nucleus. Electrons orbit around it. This helped explain how atoms behave.

Modern chemical theory

In 1916, Gilbert N. Lewis suggested that atoms can share electrons to form bonds. Around the same time, Walther Kossel proposed that some bonds form when electrons move from one atom to another. These ideas helped scientists understand how atoms stick together to make molecules.

Bonds in chemical formulas

In molecular formulas, we show the bonds between atoms in different ways, depending on what we are studying. For example, in organic chemistry, we might look only at a special part of the molecule called the functional group. The formula for ethanol can be written in several ways: in a special 3D shape, in a flat 2D shape showing every bond, a simpler flat form (CH₃–CH₂–OH), or just by separating the functional group (C₂H₅OH). Sometimes, scientists also show the electrons that are not involved in bonding.

Strong chemical bonds

Strong chemical bonds are the forces that hold atoms together to make molecules. These bonds form when electrons move between atoms or are shared among them. This creates a pull between the atoms, keeping them close.

There are different types of strong bonds. Some happen when one atom gives electrons to another, making ions that stick together. Others happen when atoms share electrons equally. The way atoms share or give electrons depends on how much they "want" those electrons. Scientists call this electronegativity. Big differences in this desire make ionic bonds, while smaller differences make covalent bonds. In metallic bonds, electrons move freely among many atoms, giving metals their shiny look and good conductivity.

Intermolecular bonding

Main article: Intermolecular force

Molecules can stick together or push apart because of weak bonds. These bonds change how a substance behaves, like how easily it melts.

There are different kinds of these weak bonds. Some happen between molecules that have small charges, while others happen because of how the molecules’ electrons move around. One special kind is the hydrogen bond, which helps explain why water stays liquid at higher temperatures than expected.

Theories of chemical bonding

Bonds between atoms can be thought of in different ways.

One type is called ionic bonding. In this type, electrons stay close to one atom, and the atoms attract each other through electric forces.

Another type is covalent bonding. In this type, electrons are shared between atoms. There are special theories to help us understand this, like valence bond theory and molecular orbital theory. These theories look at how atoms share electrons and how this affects the whole molecule.

Covalent bonds are often shaped in specific ways, forming different types like sigma and pi bonds, depending on the molecule's structure.

Sometimes, bonds are a mix of ionic and covalent, called polar covalent bonds. This depends on how much each atom "wants" the electrons.