What is a chemical element? Definition:
On chemical element is a so-called pure substance that consists only of itself and can not be split into different individual components using chemical methods. Currently, 118 different elements are known. Chemical elements can be clearly distinguished from each other by their atomic number. This number, also known as the atomic number, indicates the number of protons in the nucleus. Consequently, identical elements have the same atomic number. The figure on the left shows the chemical element gold, which has a total of 79 protons.
Much of the chemical elements were discovered only in the 17th and 18th centuries. To date, only a few pure substances have been known, including e.g. Copper, mercury, iron or even gold. From antiquity to the late Middle Ages, the four basic elements earth, fire, air and water were still considered. This four element teaching, i.a. Represented by Aristotoles and Plan (albeit in slightly modified form), people's minds lasted for nearly two millennia.
To differentiate from the chemical element is the chemical compound.
Pure elements and mixing elements:
Pure elements are elements with a single, naturally occurring isotope. Of 118 elements, only 22 are pure elements: aluminum, arsenic, beryllium, bismuth, cesium, cobalt, fluorine, gold, holmium, iodine, manganese, sodium, niobium, phosphorus, plutonium, praseodymium, rhodium, scandium, terbium, thorium, thulium and Yttrium.
The atoms of the respective pure elements are thus always identical in terms of proton number and neutron number. All other elements are among the mixing elements. These have two or more naturally occurring isotopes.
The most common chemical elements:
With a share of about 90%, the earth's crust contains mainly oxygen, silicon, aluminum, iron, calcium and sodium in various chemical compounds. With a variety of elements, we practically never 'come into contact'. There are three reasons for this: Firstly, many elements are so rare or present in extremely small amounts on our planet. Second, some of the heavy elements have only been created artificially in the laboratory and therefore do not occur in nature. And third, we know z.T. not at all in which objects of everyday life rare elements occur. For example, in a commercial computer, many rare items are 'obstructed', e.g. Palladium, neodymium or praseodymium.
In comparison, the distribution of the elements in the cosmos looks very different. Hydrogen and helium together make up 98% of the elements. Both elements have formed in the context of the so-called nucleosynthesis (formation of atomic nuclei) shortly after the Big Bang.