Compounds and elements

The difference between elements and compounds is part of a very important understanding in the study of chemistry. Also, these are pure substances that exist in nature. Most notably, the main difference between element and compound is that the former is made up of the same types of atoms, while the latter is made up of different elements. Read on for more information!

Element definition

An element refers to a substance that comprises only one type of atom . A good example of this is that of the hydrogen atom, since its atoms have only one proton and only one electron. Also, if there is a change in the number of protons in an atom, the type of element changes.

Definition of compound

A compound refers to a substance that is formed due to a combination of two or more elements that are different from each other . This combination of elements occurs in such a way that the atoms belonging to different elements are linked by chemical bonds. These bonds are formed due to the exchange of electrons between the atoms.

Differences in properties

Elements are distinguished by name, symbol, atomic number, melting point, boiling point, density, and ionization energies. In the Periodic Table , the elements are arranged according to their atomic number and grouped according to similar chemical properties and are represented by their symbols.

• Atomic number: the atomic number is indicated by the letter Z and is the number of protons present in the nucleus of the element’s atom. For example, carbon has 6 protons in its nucleus, therefore, Z = 6. The number of protons is also indicative of the electrical charge or the number of electrons present in the nucleus, which determines the chemical properties of the element.
• Atomic mass: The letter A indicates the atomic mass of the element, which is the total number of protons and neutrons in the nucleus of an atom of the element. Isotopes of the same elements differ in their atomic masses.
• Isotopes: The isotopes of an element have the same number of protons in their nucleus but differ in the number of neutrons. Elements of natural origin have more than one stable isotope. Therefore, isotopes have similar chemical properties (due to the same number of protons) but different nuclear properties (due to the different number of neutrons). For example, carbon has three isotopes, carbon 12, carbon 13, and carbon 14.
• Allotropes: the atoms of an element can form bonds with each other in more than one way, resulting in differences in their chemical properties. For example, carbon joins in a tetrahedron to form a diamond and the layers of carbon hexagons form graphite.

Compounds are made up of different elements in a fixed proportion . For example, 1 atom of sodium (Na) combines with 1 atom of chlorine (Cl) to form a molecule of sodium chloride compound (NaCl). The elements of a compound do not always retain their original properties and cannot be separated by physical means. The combination of elements is facilitated by its valence. Valence is defined as the number of hydrogen atoms required that can combine with one atom of the element that forms the compound.

Most compounds can exist as solids (low enough temperatures) and can be decomposed by the application of heat. Sometimes foreign elements get trapped within the crystalline structure of compounds, giving them an inhomogeneous structure. Compounds are represented by their chemical formula that follows the Hill system, in which the carbon atoms are listed first, followed by the hydrogen atoms, after which the elements are listed in alphabetical order.

Visualizing the differences

This image shows the differences between elements and compounds at the atomic level. Elements have only 1 type of atoms; compounds have more than 1 . Elements and compounds are substances; They differ from mixtures in which different substances are mixed, but not by atomic bonds.

History of elements and compounds

The elements were initially used as a reference to any state of matter such as liquid, gas, air, solid, etc. The Indian, Japanese and Greek traditions refer to five elements: air, water, earth, fire and ether. Aristotle conceptualized a new fifth element called ‘ quintessence ‘, which apparently formed the heavens. As the research continued, many eminent scientists paved the way for the current understanding and description of the elements. Among them, the works of Robert Boyle, Antoine Lavoisier, Dmitri Mendeleev stand out.. Lavoisier was the first to make a list of chemical elements and Mendeleev was the first to order them according to their atomic number in the Periodic Table. The most current definition of an element is provided by studies carried out by Henry Moseley who affirm that the atomic number of an atom is physically expressed by its nuclear charge.

Before the 19th century, the use of the term compound could also mean a mixture. It was in the 19th century that the meaning of a compound could be distinguished from a mixture. Alchemists such as Joseph Louis Proust, Dalton and Berthollet and their studies on various compounds have given modern chemistry the current definition of compound. Proust’s work demonstrated to the world of chemistry that the compounds were a constant composition of the respective elements.

CAS number

Each chemical is identified by its unique numerical identifier: the CAS (Chemical Abstract Service) number . Therefore, every element and chemical compound has a CAS number. This makes searching the database for elements and compounds more convenient.

More details about the elements

An element is a substance in which the atoms have the same number of protons . Consequently, this means that the atoms of an element have the same atomic number. The decomposition of elements is not possible and therefore they are the simplest substances.

Although all the atoms of an element must have the same number of protons, their number of neutrons can certainly be different . Consequently, they can also be of different masses. Also, isotopes are forms of an element whose atoms have different numbers of neutrons.

Certainly, there is a difference between elements and components. The latter refers to a small part of a larger entity that is mostly a manufactured object. On the contrary, the first is one of the simplest parts of which everything consists.

More details on compounds

There are differences between a mixture and a compound, since the first occurs with the realization of a physical mixture of several substances . On the contrary, the second occurs due to a combination of multiple substances through a chemical reaction .

Often times, a compound does not behave like any of its constituent elements. For example, the elements hydrogen (H) and oxygen (O) tend to be gases at room temperature, when atmospheric pressure is normal. However, compound water is liquid at room temperature, maintaining normal atmospheric pressure.

The atoms of some elements do not easily bond with other elements. Therefore, they do not form compounds. Most notable are inert or noble gases such as neon, argon, helium, xenon, krypton, and radon.