Chemical compound

A chemical compound is a chemical substance made up of many identical molecules (or molecular entities). These molecules contain atoms from more than one chemical element. The atoms are held together by strong forces called chemical bonds.

For example, water (H₂O) is a compound. It is made of two parts hydrogen and one part oxygen. Pure water can be shown in a ball-and-stick model. This model helps us see how the atoms are arranged.

Chemical compounds can change into different substances through chemical reactions. During these reactions, the bonds between atoms can break, form, or both. This ability to change makes chemical compounds very important. They play roles in nature and in many human activities, such as cooking, medicine, and manufacturing.

There are four main types of chemical compounds. These types depend on how their atoms are bonded together. Molecular compounds are held together by covalent bonds. Ionic compounds are held together by ionic bonds. Intermetallic compounds are held together by metallic bonds. Coordination complexes are held together by coordinate covalent bonds. Each type behaves differently and has unique properties.

Each chemical compound can be described using a chemical formula. The formula shows the number of atoms of each element in the compound. For example, the formula for water is H₂O. This means each molecule has two hydrogen atoms and one oxygen atom. Many compounds also have a special number called a CAS number. This number is given by the Chemical Abstracts Service. Today, scientists have registered many different chemical compounds for use around the world.

History of the concept

The idea of a "compound" started around 1661. Robert Boyle wrote a book called The Sceptical Chymist. In it, he used the word "compound" to describe things made by mixing different materials. He gave examples like gold, lead, and wine.

In 1724, Isaac Watts helped explain the idea better in his book Logick. He said some substances are simple, like elements, and cannot be broken down. Others are compounds, made from two or more simple substances mixed together. For example, a needle made of steel is simple, but a sword with a handle made from different materials is a compound.

Definitions

A chemical compound is a substance made of two or more different types of atoms from chemical elements joined together in fixed amounts. For example, water is a compound made of two hydrogen atoms and one oxygen atom, written as H₂O. Chemical compounds can change into different substances through chemical reactions. We show the make-up of a compound using a chemical formula, like H₂O, which tells us how many atoms of each element are in the compound.

Types

Main article: Molecule

A molecule is a group of atoms joined together by chemical bonds. It can be made of atoms from one element, like in oxygen (O₂), or from more than one element, like in water (H₂O). A molecule is the smallest part of a substance that still acts like that substance.

Main article: Ionic compound

An ionic compound is made of tiny parts called ions that stick together because of electric forces. These compounds are usually hard and stay solid at high temperatures. When melted or dissolved, they can carry electricity because the ions are free to move.

Main article: Intermetallic compound

An intermetallic compound is a special mix of metals that forms a solid material with atoms in a regular pattern. These compounds are often hard and stay strong even at high temperatures.

Main article: Coordination complex

A coordination complex has a central metal atom or ion surrounded by other molecules or ions called ligands. Many metals, especially those found in the middle of the periodic table, form these kinds of compounds.

Bonding and forces

Compounds stay together because of different kinds of bonds and forces. One of the weakest forces is called London dispersion forces, which are part of the Van der Waals force. These forces happen when electrons in nearby atoms line up and create a temporary pull between them.

Another important type of bond is the covalent bond, where atoms share electrons with each other. This usually happens between elements that are close on the periodic table of elements. Ionic bonding is different — one atom gives its electrons to another, creating positively and negatively charged ions that stick together. Hydrogen bonding is another special kind of connection that happens when a hydrogen atom interacts with another atom.

Reactions

Main article: Chemical reaction

When two chemical compounds come together, they can change into new substances. This happens through a chemical reaction. During this process, the bonds that hold the atoms together break apart. Then, new bonds form, creating different compounds than before. For example, two compounds can react to form new materials.