Chemical element

A chemical element is a type of atom with a set number of protons. This number is called the atomic number. For example, oxygen has an atomic number of 8, meaning each oxygen atom has 8 protons in its nucleus. Atoms of the same element can have different numbers of neutrons, called isotopes.

Most of the material in the universe is made of elements, with a few rare exceptions like neutron stars. By November 2016, the International Union of Pure and Applied Chemistry recognized 118 elements. The first 94 are found naturally on Earth, while the other 24 are synthetic elements made in labs.

The story of finding elements began with early human societies discovering materials like carbon, sulfur, copper, and gold. Our modern understanding of elements grew from the work of Dmitri Mendeleev, who created the first periodic table in 1869. This table arranges elements by their atomic numbers and shows patterns in their physical and chemical properties.

Description

A chemical element is a type of atom that has a special number of protons, called its atomic number. For example, oxygen has an atomic number of 8, meaning every oxygen atom has 8 protons. Elements can be single kinds of atoms, like pure gold, or parts of other substances, like hydrogen and oxygen in water.

Chemical elements are organized by their properties, such as atomic number and how they react with other elements. The periodic table is a common way to show elements, grouping those with similar properties together. Some elements exist naturally, like hydrogen and helium. Others are made by scientists in laboratories.

Atomic nucleus properties

The center of an atom, called the nucleus, is made up of protons and neutrons. Protons have a positive charge, and neutrons have no charge. They stay together because of a strong force, even though the protons push apart because they have the same charge.

An atom’s identity is decided by the number of protons in its nucleus. This number is called the atomic number. For example, all carbon atoms have 6 protons, so carbon’s atomic number is 6. Atoms of the same element can have different numbers of neutrons. These are called isotopes. They have almost the same chemical properties but can act differently in nuclear reactions.

Chemical and physical properties

Quantum mechanics helps explain how electrons are arranged in layers around the nucleus of an atom. These layers are called shells. Shells can only hold a certain number of electrons. The way electrons are arranged in shells determines many of an element's properties and its place in the periodic table.

Elements are grouped based on whether they conduct electricity. Metals conduct electricity, nonmetals do not, and metalloids are in between. Metals tend to lose electrons to form positive ions, while nonmetals gain electrons to form negative ions. The periodic table organizes elements into rows and columns that show patterns in their properties. This makes it a useful tool in many areas of science and technology.

Nomenclature and symbols

Chemical elements are known by their atomic numbers, names, and symbols. The atomic number shows how many protons are in an atom’s center. For example, oxygen has an atomic number of 8, so each oxygen atom has 8 protons.

Elements get names from many places, such as their properties, places, or scientists. Scientists agree on these names so everyone uses the same terms around the world. Each element also has a special symbol, like “O” for oxygen, which helps scientists share their ideas clearly in any language.

Origin of the elements

Main article: Nucleosynthesis

Most of the universe is made of something we can't see, called dark matter and dark energy. Only a small part, about 4.6%, is ordinary matter, like the atoms around us.

The elements we find on Earth and in space were created in different ways. The simplest elements, hydrogen and helium, were formed just after the Big Bang. Heavier elements, like carbon and iron, are made inside stars. Even heavier elements, such as uranium, are created when stars explode or collide. Some lighter elements, like lithium and beryllium, are made when cosmic rays hit other atoms.

Abundance

Main article: Abundance of the chemical elements

The amount of each element in the universe depends on how it was created. Hydrogen and helium, the two most common elements, were made during the Big Bang. Heavier elements are created inside stars.

On Earth, the mix of elements is different from the rest of the solar system. Lighter elements like hydrogen and helium are much less common because they were lost early in Earth’s formation. Oxygen is the most common element on Earth because it bonds with other elements like silicon and iron. Living things are made mostly of six key elements: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Some organisms also need extra elements, like magnesium for chlorophyll in plants or calcium for shells in molluscs.

History

The idea of an "element" has changed over time. Ancient thinkers like the Greeks thought of basic building blocks of nature as things like earth, water, air, and fire. Later, scientists began to think of elements as basic, unchanging substances that make up all matter.

In the 1600s, Robert Boyle suggested that matter is made of tiny particles that can combine in many ways. By the late 1700s, Antoine Lavoisier made one of the first lists of elements. In the 1800s, Dmitri Mendeleev created the periodic table to organize these elements, showing patterns in their properties.

Many elements were known to ancient cultures, like gold and copper. Others, such as phosphorus, were discovered much later. Scientists continue to find and study new elements.