Chemical elements. Atomic elements. Simple substances. Elements of the periodic table. These are all different terms for the same concept. A long time ago, “elements” used to mean earth, air, wind and fire – but that is no longer true. The idea of an “element”, a basic building block of matter, has piqued the curiosity of mankind for many ages. But in chemistry – what exactly is an element – how do we define it?
History of the elements
Aristotle decreed that there were four earthly elements – air, wind, earth and fire. His notion of elements remained unchanged for just over two thousand years, until the French chemist Antoine Lavoisier performed a series of experiments that made him realize there were “simple substances” that he would later call elements. Nitrogen, hydrogen, oxygen, carbon, sulfur and phosphorus were six early elements that he classified as such, but he also misclassified some compounds as elements, like ammonia.
Fast forward 87 years. Russian chemist Dmitry Mendeleev arranged the 52 known elements into rows and columns, which he called the periodic table. Soon more elements were discovered, and the last to be discovered naturally occurring element, rhenium, was isolated in 1925.
Definition of an Element
We can define an element, as a type of matter that can not be broken down into a simpler substance by chemical means. The only way to break down an element, or change it into a different element, is via a nuclear reaction. You can crush an element, throw it, burn it, stomp on it, or dissolve it in acid – but you still won’t transform, decompose or change the substance into another element. But you might make a mess.
It is important to note, that an element can take many different forms. Let’s talk about an example – sodium. Pure sodium is a shiny, highly reactive metal. Sodium is also found in table salt, in the form of sodium ions, which are bonded to chlorine atoms. These sodium ions are not shiny or reactive like elemental sodium, but table salt still “contains” the element sodium. And if we dissolve salt in water, the sodium ions are dissolved in solution. The solution “contains” the element sodium, but it is not in elemental form. The elemental form of an element is when it exists not chemically combined with any other atom or ion.
How many Elements are there?
There are currently 118 elements known to humankind. 94 elements are naturally occurring, and 24 elements have been artificially produced, or synthetically produced, via nuclear reactions. These 24 elements are sometimes called man-made elements. Elements can be solids, liquids or gases at room temperature, 20 degrees Celsius.
The first element on the periodic table is hydrogen. The last element, the one most recently synthesized in 2002, is element 118, oganesson – named after the Russian-Armenian physicist Yuri Oganesson.
Out of the 94 naturally occurring elements, 6 of them occur only in extremely small trace quantities – for example francium or neptunium. Those six are all radioactive and only exist as decay products of other more abundant radioactive elements.
Properties of Elements
Elements have a variety of different chemical and physical properties. But what do they have in common?
To start with, every element has a unique number of protons. If you modify the number of protons of an element via a nuclear reaction, you end up with a different one. A pure element consists of only one type of atom – atoms of that element.
Most elements have isotopes – different forms of the element that have the same number of protons and electrons, but a different number of neutrons. Isotopes of an element generally have the same chemical properties, but may have slightly different physical properties.
Another property of an element – is that it has a unique symbol, atomic number, and its own square on the famous periodic table. The symbol, known as an atomic symbol, is usually an abbreviation for its name, like Cl for chlorine. But sometimes the atomic symbol abbreviated the Latin name. For example, Na is the abbreviation for Natrium, the Latin name for the element sodium. The atomic number represents the number of protons an element has, ranging from 1 to 118. The periodic table is a chart of all of the elements, arranged in rows and columns by “families”. Read about how to read the periodic table.
Examples of Elements
Some of the more well-known elements include sodium, magnesium, iron, copper, helium, carbon, hydrogen, nitrogen, and gold. Iron, copper and gold are all solid metals. Helium and argon are examples of inert gases. Carbon is a solid “nonmetal”, while mercury is a liquid metal at room temperature. The 118 elements all have different fascinating physical and chemical properties, and you could spend a lifetime studying the compounds of just one element.
A molecule may consist of one element, or multiple elements. A compound always contains two or more elements. An atom can only be a single element, and all elements are made of atoms of that element. Ions are charged particles made up of a single element, or multiple elements.
Want to learn more?
Our friend Eric Scerri co-authored a great book called “What is a chemical element“. Citation for the book is Eric Scerri, Elena. Ghibaudi (eds.) What is a Chemical Element?, OUP, 2020. Dr. Scerri delves into the definition of an element in more detail. For example – what exactly is carbon? Is it a particular isotope? Is it an “average” of all of its isotopes? Does it have particular properties, and if so what are those properties? And what about its allotropes? And are the super-heavy elements, which decompose in fractions of a second, really “chemical elements”? Did Mendeleev have the correct abstract notion of an element? This book brings up many excellent points about the elements to mull over. “The disappearing spoon” and “Uncle Tungsten” are also great books to learn more about the elements.