Chemical element
Introduction
A chemical element is a pure substance that cannot be broken down by chemical means into simpler substances. Each element is characterized by a unique atomic number, representing the number of protons in its nucleus. As of 2021, 118 elements have been identified, the majority of which are metals.
History
The concept of chemical elements dates back to ancient times. Early philosophers such as Empedocles and Aristotle proposed that all matter was composed of four basic elements: earth, air, fire, and water. However, the modern understanding of chemical elements began to take shape in the 17th century with the work of Robert Boyle and Isaac Newton.
Definition and Characteristics
A chemical element is defined by the number of protons in its nucleus, known as the atomic number. This number is unique for each element and determines its position in the periodic table. The atomic weight of an element is the average mass of its atoms, usually expressed in atomic mass units (amu).
Classification
Chemical elements can be classified in several ways, including by their physical and chemical properties, their atomic structure, and their occurrence in nature. The most common classification divides elements into metals, nonmetals, and metalloids.
Occurrence and Abundance
The abundance of chemical elements varies widely, both on Earth and in the universe at large. Hydrogen and helium are the most abundant elements in the universe, while oxygen and silicon are the most abundant elements in the Earth's crust.
Discovery and Naming
The discovery of new elements has been a central part of chemistry for centuries. The naming of elements has often been a contentious issue, with different scientists and countries proposing different names for the same element.
Applications
Chemical elements have a wide range of applications, from the construction of buildings and vehicles to the production of electronics and medicines. The properties of each element determine its uses.
Toxicity and Environmental Impact
Some elements are toxic to humans and other organisms, and their release into the environment can have serious ecological consequences. The study of the environmental impact of chemical elements is a key part of environmental chemistry.