Chemical element

A chemical element is a special type of atom. Every element has its own number of protons, which is like its ID number. For example, oxygen has 8 protons. Scientists have found 118 elements so far.

94 of these are found naturally on Earth, like the gold used for coins.

The other 24 are synthetic, which means they are made by scientists in labs. One amazing fact is that most of the universe is made of just two elements: hydrogen and helium!

All these elements are organized on a chart called the Periodic Table, which helps us see how they are similar.

A chemical element is a substance made of only one kind of atom. The identifying feature of an element is its atomic number, which is the number of protons in its nucleus. For example, every carbon atom has 6 protons. Sometimes atoms of the same element have different numbers of neutrons; these are called isotopes.

Most elements are solids, like iron, but some are gases, like nitrogen. Only two elements, mercury and bromine, are liquids at room temperature. Elements can also change their physical form; carbon can be soft graphite in a pencil or a hard diamond. This is called allotropy.

In 1869, a scientist named Dmitri Mendeleev created the Periodic Table to organize all known elements.

He arranged them in rows and columns based on their properties. Today, we know of 118 elements. The first 94 occur naturally, while the rest are synthetic. Most of the elements that make up your body are oxygen, carbon, hydrogen, nitrogen, phosphorus, and sulfur.

Chemical elements are the fundamental building blocks of all matter in the universe. An element is defined by its atomic number, which is the specific number of protons found in the nucleus of its atoms. For instance, hydrogen has an atomic number of 1, while gold is 79.

While the number of protons stays the same for an element, the number of neutrons can vary. These different versions are called isotopes. Most elements have several isotopes, some of which are stable and others that are radioactive and decay over time.

The way elements behave depends on their electrons, which orbit the nucleus in layers called shells.

The arrangement of these electrons determines how an element reacts with others to form compounds. This behavior is why the Periodic Table is so important. Created by Dmitri Mendeleev in 1869, the table organizes elements into groups (columns) and periods (rows).

Elements in the same column usually have similar properties. For example, metals like copper and gold are excellent at conducting electricity.

The history of elements goes back to ancient times when people used gold, silver, and copper. However, the modern idea of an element took a long time to develop. Ancient Greeks thought everything was made of earth, air, fire, and water. In 1661, Robert Boyle argued that matter was actually made of tiny particles called "corpuscles." Later, in 1789, Antoine Lavoisier published the first modern list of 33 elements.

Where do elements come from? Most hydrogen and helium were created during the Big Bang at the start of the universe.

Heavier elements, like carbon and oxygen, are forged inside stars. The heaviest elements, such as uranium, are created during massive star explosions called supernovae. On Earth, we have identified 118 elements. The first 94 are found in nature, but elements 95 through 118 are synthetic, meaning they must be created by scientists in nuclear reactors.

These synthetic elements are often very unstable and only last for a fraction of a second before decaying.

A chemical element is a species of atom characterized by the number of protons in its nucleus, a value known as the atomic number (Z). This number is fundamental because it determines the electric charge of the nucleus, which in turn dictates the number of electrons the atom holds in its non-ionized state. These electrons occupy specific atomic orbitals and shells, governed by quantum mechanics, which define the element's chemical reactivity and its position on the periodic table.

While the atomic number defines the element, atoms of the same element can possess different numbers of neutrons (N). These variants are called isotopes. For example, carbon always has 6 protons, but it can have 6, 7, or 8 neutrons, resulting in carbon-12, carbon-13, and carbon-14.

The stability of these isotopes depends on the neutron-proton ratio. While light elements often have stable isotopes with equal numbers of protons and neutrons, heavier elements require more neutrons to counteract the electrical repulsion between protons. Elements like uranium have no stable isotopes and undergo radioactive decay.

The organization of these elements is best represented by the periodic table, first recognized in 1869 by Dmitri Mendeleev.

Mendeleev arranged elements by increasing atomic weight so that those with similar properties appeared in vertical columns called groups. This periodic recurrence of properties allowed him to predict the existence of elements that had not yet been discovered. Today, the table is divided into blocks (s, p, d, and f) based on electron subshells.

The origin of the elements is a story of cosmic proportions. Approximately 75% of the universe's elemental mass is hydrogen and 25% is helium, both produced during Big Bang nucleosynthesis. Heavier elements are the products of stellar evolution. Stars fuse hydrogen into helium, and in more massive stars, this process continues up to iron. Elements heavier than iron are produced through neutron capture during supernovae or neutron star mergers.

On Earth, we recognize 118 elements. The first 94 occur naturally, though some like technetium and plutonium only appear in trace amounts as decay products. The remaining 24 elements are synthetic, produced through human-made nuclear reactions.

Historically, the definition of an "element" has shifted from the classical Greek roots of earth, air, fire, and water to the rigorous atomic definitions of today. Robert Boyle’s 1661 work, The Sceptical Chymist, was a turning point, moving away from alchemy toward a particle-based view of matter.

Later, Henry Moseley’s 1913 discovery proved that the nuclear charge (atomic number) was the true physical basis for an element's identity, rather than atomic weight. This resolved ambiguities where some elements with higher atomic weights actually had lower atomic numbers than their neighbors.

Naming and symbols are now standardized by the International Union of Pure and Applied Chemistry (IUPAC). While ancient elements like gold (Au) and iron (Fe) retain symbols based on their Latin names (aurum and ferrum), newer elements are often named after scientists (einsteinium) or locations (californium).

Elements can also exist in different structural forms called allotropes. Carbon, for instance, can appear as the hardest natural mineral, diamond, or as the soft, conductive lubricant, graphite.

These physical differences arise from how the atoms are bonded together, even though the underlying element remains the same.