What is a chemical compound?

chemical compound is a substance formed by the union of two or more atoms of different chemical elements. Chemical compounds are held together thanks to chemical bonds , which are related to the electrons of the bonded atoms; that is to say, in a chemical compound the electrons (outermost) of the atoms take part in the formation of the bonds.

The components of chemical compounds (chemical elements) cannot be separated from each other by physical methods, such as distillation, centrifugation, filtration, etc., requiring instead chemical methods to achieve this.

An example of a chemical compound is water. It is made up of only two atoms of two different chemical elements: oxygen and hydrogen, having the chemical formula H 2 O. Therefore, two H’s join with one O to form H 2 O.

A chemical element, unlike chemical compounds, is the simplest and most basic form that constitutes matter . It occurs as a unique type of atom that cannot be broken down into simpler substances by chemical reactions.

Types of chemical compounds

Chemical compounds can be classified mainly following two criteria:

  • According to the type of bond that joins the chemical elements present in the chemical compound.
  • According to the composition and structure of the chemical compound.

According to the type of link

Depending on the type of bond, the chemical compounds can be:

  • Molecules . They are chemical compounds formed by two or more types of different chemical elements, which are joined by a covalent bond. This bond is characterized by the sharing of one or more pairs of external electrons, or valence, between two atoms.
  • Ions . Electrically charged chemical compounds are called ionic chemicals, and their ions are held together by ionic bonding . This bond occurs when a metal-type chemical element unites with a non-metal chemical element.
  • Intermetallic compounds . It is a type of metallic alloy that constitutes a solid material that is located between two or more metallic chemical elements to keep them together.
  • Coordination . They are made up of a central metallic element, called the coordination center, and which are surrounded by a set of bound molecules or ions known as ligands. Hemoglobin, for example, is a protein found in red blood cells that carries oxygen in the blood. Hemoglobin has a coordinating compound called a heme group. In the center of the heme there is an iron atom that is involved in the transport of oxygen by hemoglobin.

According to the composition and structure

According to this criterion, chemical compounds are classified as organic and inorganic.

  • Organic compounds . They are compounds whose main chemical element is carbon, which usually forms bonds with atoms of the same carbon and hydrogen. However, oxygen, nitrogen, sulfur, boron, phosphorus, etc. are also present, although to a lesser extent. Organic compounds can be:
    • Aliphatic. The molecules of the aliphatic compounds can have linear or cyclic forms, that is, in closed forms such as triangles, squares, pentagons, etc. They can have three types of carbon bonds: single (CC), double (C = C) or triple (C≡C).
    • Aromatics. They are cyclic compounds that alternately have single carbon-carbon bonds and carbon-carbon double bonds.
    • Heterocyclic. They are compounds that have a cyclic structure, which can present the substitution of a carbon atom for another chemical element (O, S, N, etc.).
    • Organometallic. They are organic compounds that can have metallic elements in their composition.
    • Polymers. They are large molecules (macromolecules) that are made up of small and identical units that are repeated throughout the polymer, and are called monomers.
  • Inorganic compounds. The inorganic compounds , unlike organic not have carbon as the central chemical element, but its composition involved in most known chemical elements. Inorganic compounds can be:
    • Basic oxides. They are formed by the reaction of a metallic chemical element, such as sodium, calcium, iron, copper, etc., with oxygen. For example, sodium oxide (NaO) is a basic oxide. They are called basic oxides because they will give rise to the bases or hydroxides.
    • Acidic oxides. They originate from the reaction of a non-metallic chemical element, such as chlorine, fluorine, sulfur, bromine, etc., with oxygen. For example, bromic oxide (Br 2 O 5 ) is an acidic oxide. They are called acid oxides because they give rise to acids.
    • Hydrides They present in their chemical composition the presence of hydrogen. There are two types: metal hydrides and non-metal hydrides.
    • Metallic. They are formed by the reaction of hydrogen, with the oxidation state -1, with a metal. These chemical compounds are the only ones in which hydrogen with the oxidation state -1 is present. For example, CaH 2 is calcium hydride.
    • Not metallic. They are formed by the reaction of hydrogen, with oxidation state +1, with a non-metallic element with its lower oxidation state. Chlorine hydride (HCl) is a gas that, when dissolved in water, gives rise to hydrochloric acid.
    • Acids. They are inorganic chemical compounds, although there are organic acids, which have a pH lower than 7 and turn the color of litmus paper to red. They can be classified as hydracids and oxacids.
    • Hydracids. They originate from the reaction of hydrogen with a non-metal to form a hydride that, when dissolved in water, produces an acid; for example, hydroiodic acid (HI).
    • Oxacids. It is caused by the reaction of an oxide of a non-metallic chemical element with water. For example, the reaction of sulfuric oxide (SO 3 ) with water produces sulfuric acid (H 2 SO 4 ).
    • You go out. They are chemical compounds that originate from the interaction of acidic and basic compounds. In its composition there can be as many metallic elements as non-metallic ones. The salts are classified as:
      • Neutral salts. They originate in a neutralization reaction between an acid and a base with the formation of salt and water. For example, the reaction of sodium hydroxide (NaOH) with hydrochloric acid (HCl) produces sodium chloride (NaCl), a salt, and water. They are called neutral because they do not produce a pH variation.
      • Acid salts. They are formed by the reaction of a hydroxide of a metal with valence +1, with an acid with several hydrogens. The reaction of lithium hydroxide (LiOH) with carbonic acid (H CO ) produces the substitution of only one hydrogen for one lithium, which gives rise to lithium bicarbonate (LiHCO ), an acid salt and water.
      • Basic salts. They are produced by the reaction of a base that has more than one OH group with an acidic acid, for example, hydrochloric acid. By reacting the acid with the calcium hydroxide, Ca (OH) , a chlorine atom replaces a hydroxyl group (OH). This produces calcium hydroxychloride (CaClOH), a basic salt, and water.

Differences between chemical compounds and chemical elements

Each chemical element corresponds to a specific atom and only to that type of atom; that is, a chemical element does not have different types of atoms. The atom is the elementary particle of matter that is not divided by physical or chemical methods.

The atom of a chemical element can join with the atoms of other chemical elements to form chemical compounds, which can be separated into their components (chemical elements) using chemical methods.

Chemical elements and chemical compounds could be equated with a puzzle: puzzle pieces have different characteristics, so they can be equated to chemical elements.

The pieces of the puzzle can be put together to form different shapes. The shapes formed could be equated with chemical compounds. Once the activity is finished, the puzzle figures can be separated into their constituent pieces.

Examples of chemical compounds

Below you can see a series of examples of everyday chemical compounds:

  • HCl: Hydrochloric acid
  • 2 S: Hydrogen sulfide
  • HF: Hydrofluoric acid
  • 2 SO 4 : Sulfuric acid
  • HClO 4 : Perchloric acid
  • 3 PO 4 : Phosphoric acid
  • 2 CO 3 : Carbonic acid
  • HNO 3 : Nitric acid
  • NaOH: Sodium hydroxide
  • Ca (OH) 2 : Calcium hydroxide
  • Fe (OH) 2 : Ferrous hydroxide
  • Fe (OH) 3 : Ferric hydroxide
  • NaH: Sodium hydride
  • Cu 2 O: Cuprous oxide
  • CuO: Cupric oxide
  • Fe 2 O 3 : Ferric oxide
  • Cl 2 O 7 : Perchloric oxide
  • Br 2 O: Hypobromous oxide
  • 2 O 3 : Hypoiodine oxide
  • NaCl: Sodium chloride
  • FeCl 3 : Ferric Chloride
  • HCO 3 : Sodium bicarbonate
  • CH 3 COONa: Sodium acetate
  • Na 2 SO 4 : Sodium sulfate
  • FeSO 4 : Ferrous sulfide
  • 2 O: Water
  • CO 2 : Carbon dioxide
  • 6 H 12 O 6 : Glucose
  • 12 H 22 O 11 : Sucrose

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