What is an element?
Element is a compound that consists solely of the same kind of atoms and protons and neutrons are specific to that atom. For example, oxygen is an element, while water is not. There are 118 elements at the time of writing, 92 of which are naturally existing and the rest are man-made. There are numbers given for the classification of the elements according to their characteristics and this table of elements is known as the periodic system of the elements.
In addition to a division by atomic number, the constituents have been divided into groups according to their characteristics. The three main categories are metals , semi-metals and non-metals. These three categories and their subgroups are reviewed in the following sections.
The metals are the type of elements that cover the the following four characteristics in common.
- They have metal gloss (Skinny by grinding or cutting).
- They are good heat and power conductors.
- They form positive ions.
- They are solid at room temperature (with the exception of mercury (Hg))
Subdivisions of the metals are: Alkali metals, lanthanides, alkaline earth metals, actinides and transition metals. Of this metals, only the first two will be further elucidated in this article.
Alkali metals cover all the constituents of the first main group of the periodic system, near hydrogen, and include lithium, sodium, potassium, rubidium, cesium and francium. It is characteristic of these elements that they all have only one electron in the outer shell. This means in practice that they only emit a single electron, and therefore basically form ions with a positive charge of 1 an example of which is Na+ and K+. The reason why only this type of ions are formed is that the constituents will achieve a noble gas-like state when they are given an electron. Thus all their shells are completely filled. They also have approximately noble gas-like properties and therefore they are not easy to oxidize further. On the other hand, the alkali metals are reactive to such as sodium can for react with water in an almost explosive reaction.
The lanthanides include the elements with atomic numbers from 57 to 71. These are characterized by being able to form an ion with a positive charge of 3 such as La3+and Pr3+. Furthermore, they are known to have far more complicated magnetic properties compared to other groups of elements. Since they all have atomic numbers less than 92, they are naturally found on Earth, and by far the majority of the constituents of this group are included in different types of monazite mineral.
The semi-metals are characterized by both having metallic and non-metallic properties. The group comprises seven elements: boron, silicon, germanium, arsenic, antimony, tellurium and polonium. Looking at the periodic table, these elements are located precisely in the interface between the metals and the non-metals.
This group of elements is characterized by high electronegativity. That is, these elements attract electrons better than others, so they do not easily deliver an electron. In addition, they do not have any metallic properties. There are three subdivisions of the non-metals: Noble gases, Halogens and other non-metals.
The halogens comprise the entire 17th main group in the periodic system, meaning fluorine, chlorine, bromine, iodine and astat. These elements are characterized by having seven outermost electrons, and with their high electronegativity, an ion with a negative charge of 1 is often formed such as Cl- and Br-. However, they can also achieve other oxidation steps, such as +5 and especially +7. Finally, an oxidation step of 0 is also common when the elements are in their pure form, ie as Br2 and I2. The many possible oxidation steps make halogens particularly useful for redox reactions. Another feature of the electron configuration and electronegativity is the ability to form an acid with hydrogen. If there is HCl, then the chlorine atom will attract the one electron of the hydrogen atom to an extent that it is an ion.
A radioactive element differs from other elements by spontaneously decaying. That is, the element is converted to either another element or to another isotope. That is, an atom where the number of neutrons does not equal the number of protons. An element is radioactive if its core is unstable. It may happen if it has an excess of energy or core particles. By the latter one can imagine that the helium’s (He) nuclear nuclei contain four neutrons instead of regular two. Lets have a look at the decaying forms; alpha decay is characterized by the nuclear core emitting two protons and two neutrons (ie a helium core). Thus the element transforms into the element whose atomic number is two numbers lower. Uranium (U) will thus fall into thorium (Th) while dispatching a helium core.
This type of decay is the most common for elements whose atomic number is greater than 82. Within radioactivity alpha decay is associated with beta decay and gamma decay.