What Is an Element?
A chemical element is the simplest form of matter that cannot be broken down using any chemical means. Any substance made up of one type of atom is an example of that element. All atoms of an element contain the same number of protons. For example, helium is an element -- all helium atoms have 2 protons. Other examples of elements include hydrogen, oxygen, iron, and uranium. Here are some essential facts to know about elements:
Essential Element Facts
- While every atom of an element has the same number of protons, the number of electrons and neutrons can vary. Changing the number of electrons forms ions, while changing the number of neutrons forms isotopes of an element.
- The same elements occur everywhere in the universe. Matter on Mars or in the Andromeda Galaxy consists of the same elements found on Earth.
- The elements were formed by nuclear reactions inside stars. Initially, scientists thought only 92 elements occurred in nature, but now we know many of the short-lived radioactive elements are also made in stars.
- There are different forms of pure elements, called allotropes. Examples of allotropes of carbon include diamond, graphite, buckminsterfullerene, and amorphous carbon. Although they all consists of carbon atoms, these allotropes have different properties from each other.
- Elements are listed in order of increasing atomic number (number of protons) on the periodic table. The periodic table arranged elements according to periodic properties or recurring trends in the characteristics of the elements.
- The only two liquid elements at room temperature and pressure are mercury and bromine.
- The periodic table lists 118 elements, but when this article was written (August 2015), the existence of only 114 of these elements had been verified. There are new elements yet to be discovered.
- Many elements occur naturally, but some are man-made or synthetic. The first man-made element was technetium.
- Over three-quarters of the known elements are metals. There are also a small number of nonmetals and elements with properties in between those of metals and nonmetals, known as metalloids or semimetals.
- The most common element in the universe is hydrogen. The second most abundant element is helium. Although helium is found throughout the universe, it is very rare on Earth because it does not form chemical compounds and its atoms are light enough to escape Earth's gravity and bleed out into space. Your body contains more hydrogen atoms than atoms of any other element, but the most common element, by mass, is oxygen.
- Ancient man was exposed to several pure elements that occur in nature, including carbon, gold, and copper, but people did not recognize these substances as elements. The earliest elements were considered to be earth, air, fire, and water -- substances we now know consist of multiple elements.
- While some elements exist in pure form, most bond together with other elements to form compounds. In a chemical bond, atoms of one element share electrons with atoms of another element. If it's a relatively equal sharing, the atoms have a covalent bond. If one atom basically donates electrons to an atom of another element, the atoms have an ionic bond.
Organization of Elements in the Periodic Table
The modern periodic table is similar to the periodic table developed by Mendeleev, but his table ordered elements by increasing atomic weight. The modern table lists the elements in order by increasing atomic number (not Mendeleev's fault, since he did not know about protons back then). Like Mendeleev's table, the modern table groups elements according to common properties. Element groups are the columns in the periodic table. They include alkali metals, alkaline earths, transition metals, basic metals, metalloids, halogens, and noble gases. The two rows of elements located below the main body of the periodic table are a special group of transition metals called the rare earth elements. The lanthanides are the elements in the top row of the rare earths. The actinides are elements in the bottom row.