# Elements --- **Elements** are pure substances. Everything—literally everything—is built from them. The study of the elements, and the combinations thereof is called [[chemistry]]. The smallest division of an element is called an [[atom]]—if you divide it any further then what you have no longer retains the properties inherent of the element. There are currently ~118 elements that we know of, but presumably there are some more heavy (and highly unstable) elements that theoretically exist out there. Elements are classified based on their physical and chemical properties. They are arranged on the **periodic table of elements** such that elements with similar properties are located closer to each other, and disparate elements are further. One can predict the properties and traits of an element on the table simply by understanding the properties associated with its location on the table. ![[periodic table of elements.png]] Atoms of some elements can combine with atoms of some other elements (or, indeed, with others of the same element), forming [[molecule|molecules]]. Combinations of elements like these are called mixtures, like we find in [[solution|solutions]]. The elements in the body that are particularly important to [[biology#The Chemistry of Biology|biology]] are hydrogen, carbon, [[oxygen]], [[nitrogen]]. [[phosphate|Phosphorus]] and [[calcium]], and [[sodium]] all act as important electrolytes. ## Gases Gasses are elements that are in the [[matter|state]] of gas in normal conditions. ### Halogens The **halogens** are a highly reactive group of elements, found in the 7A group. They are so reactive because they *only need 1* more electron to fill their [[electron shell|valance shells]], and will do pretty much anything to get it. If they do succeed in gaining an extra electron or two they become and [[ion]]. ### Noble Gas The **noble gasses** are a highly stable group of elements, found in the 8A group. They are so nonreactive because their [[electron shell|valance shells]] are naturally full, and they are very happy to keep it that way. ## Metals & Nonmetals **Metals** are a type of [[element]] that are found on the left and middle of the periodic table of elements. They are shiny, ductile and malleable. They are good conductors of heat and electricity. **Nonmetals** are, as the name suggests a type of [[element]] that is not a metal. They are found on the right hand side of the periodic table of elements. They are not especially shiny, ductile or malleable, and are poor conductors of heat and electricity. ### Alkali Metals The **alkali metals** are found in the first group of the periodic table of elements that have special properties of metals. They are highly reactive because they have one extra electron in their valance shells, and will do almost anything to get rid of it. If they succeed in getting rid of it they become [[ion|ionized]]. Notable alkali metals in biology are [[sodium]] and [[potassium]]. ### Metalloids **Metalloids** are a type of [[element]] that has properties somewhere between metals and nonmetals. They are found in the zig-zag stair pattern of the periodic table of elements. They are better conductors than nonmetals, but not as good as metals. Therefore, they are often used as semiconductors and insulators. ___