Chemical element
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A chemical element is a substance that cannot be divided into smaller chemical parts. The smallest particle of such an element is an atom. Atoms are made up of Protons, neutrons, and electrons.
A pure element contains only one kind of atom. The number of protons in the atoms of an element is known as that element's atomic number. For example, all atoms with 6 protons in their nuclei are of the chemical element carbon, and all atoms with 92 protons in their nuclei are of the element uranium.
116 different chemical elements are known to modern chemistry. 90 of these elements can be found in nature, and the others can only be made in laboratories. The first man-made element was Technetium in 1937. All man-made elements are radioactive and unstable.
Chemical elements are commonly arranged in the periodic table.
Atoms of the same element, whose nuclei contain a different number of neutrons, are said to be different isotopes of the element.
Chemical elements are also given a unique chemical symbol. Chemical symbols of elements come from their English or Latin names (For example, carbon has the chemical symbol 'C', and sodium has chemical symbol 'Na', after the Latin natrium).
Elements can combine (react) to form pure compounds (such as water, salts, oxides, and organic compounds). In many cases, these compounds have a fixed composition and their own structure and properties.
Some elements, particularly metal elements mix together in any proportion to form new structures. Such new structures are not compounds. They are called mixtures.
[edit] Classification
Elements can be classified based on physical states. At room temperature and pressure, most elements are solids, only 11 are gases and 2 are liquids.
Elements can also be classified into metals and non-metals. There are many more metals than non-metals.
However, a few elements have properties in between those of metals and non-metals. These elements are called semi-metals (or metalloids).
