Chemical compound

A chemical compound is a chemical substance made up of many identical molecules (or molecular entities) that contain atoms from more than one chemical element. These atoms are held together by strong forces called chemical bonds. For example, water (H₂O) is a compound made of two parts hydrogen and one part oxygen. Pure water can be shown in a ball-and-stick model, which helps us see how the atoms are arranged in space.

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 in nature and in many human activities, such as cooking, medicine, and manufacturing.

There are four main types of chemical compounds, depending on how their atoms are bonded together. Molecular compounds are held together by covalent bonds, ionic compounds by ionic bonds, intermetallic compounds by metallic bonds, and coordination complexes by coordinate covalent bonds. Each type behaves differently and has unique properties.

Each chemical compound can be described using a chemical formula, which shows the number of atoms of each element in the compound. For example, the formula for water is H₂O, meaning each molecule has two hydrogen atoms and one oxygen atom. Many compounds also have a special number called a CAS number, given by the Chemical Abstracts Service. Today, scientists have registered over 350,000 different chemical compounds for use around the world.

History of the concept

The idea of a "compound" dates back to at least 1661, when Robert Boyle wrote The Sceptical Chymist. In his book, Boyle used words like "compound" and "compounded body" to describe substances made from mixing different materials. He talked about things like gold, lead, and even wine as examples of these "perfectly mixt bodies."

Later, in 1724, Isaac Watts helped make the idea clearer in his book Logick. He explained that 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 stuck 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 have high melting points. 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 ordered atoms. These compounds are often hard and keep their shape well 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 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 in a way that creates 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 to each other on the periodic table of elements. Ionic bonding is different — here, 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 electronegative atom.

Reactions

Main article: Chemical reaction

When two chemical compounds come together, they can change into new substances through a chemical reaction. During this process, the bonds that hold the atoms together in each compound break apart. Then, new bonds form, creating different compounds than before. For example, if we have two compounds called AB and CD, they might react to form AD and CB, where each letter stands for a different atom. This shows how chemicals can interact and transform into new materials.