Mendeleev's Periodic Table of Elements
Definition - What does Mendeleev's Periodic Table of Elements mean?
An element, in the context of chemistry, is a type of atom, dictated by the number of protons it contains in its nucleus, also known as its atomic number. This value determines a basis for the majority of the atom’s properties. The nuclear stability and atomic mass is determined by the number of neutrons. Its chemical state, reactivity, and the electronic properties are determined by the number of electrons. Varying numbers of neutrons in an element are referred to as isotopes of the element and varying electrons determine an element’s oxidation state.
Although the atomic number determines the base properties of an element, the element's properties as the atomic number increases follow a trend in the corresponding increase in the number of electrons the element has. These repeating trends form an organization of chemical elements into the periodic table of elements. The table lays out the property relationships between elements in similar columns, rows and regions of the table. The elements on the periodic table are broken down into the following major categories:
- Alkali metals
- Alkaline earth metals
- Transition metals
- Post-transition metals
- Noble gases
Each element on the periodic table is associated with an identifying chemical symbol with one to three letters.
Corrosionpedia explains Mendeleev's Periodic Table of Elements
Elemental properties derive from its proton and neutron filled nucleus and surrounding orbiting electrons. As the atomic number increases, each proton with a charge of +1 increase the positive charge of the nucleus, thus increasing the capacity of the element to hold more electrons, each with a -1 charge.
The electrons occupy special regions called orbitals. There are different orbital energy levels (1, 2, 3 …) and each energy level has different types of orbitals referred to by special letters (s, p, d, f). Each orbital type can only host a certain number of electrons (s = 2, p = 6, d = 10, f = 14). The periodic table organizes the elements according to these orbitals. Each row of the periodic table refers to a different orbital energy level (1, 2, 3 …) and different regions of columns refer to orbital types (s, p, d, f).
The alkali and alkaline earth metals are the first two columns of the periodic table, respectively. They correspond to the filling of the two s orbital electrons. These metals are highly reactive in their neutral metallic forms and react to form cationic ions. Although hydrogen is included in this region, its properties are unique compared to any other element on the periodic table.
The long region of the transition metals corresponds to the filling of the ten d orbitals. These elements are rich in metallic properties such as electric and thermal conductivity, catalytic activity and malleability.
The region to the right of the transition metals can be most easily referred to as the p-block, which comprises the filling of p-type orbitals and is a region difficult to categorize. The elements in these regions can be metallic, non-metallic or in between (metalloid). The metalloids divide the two regions in a diagonal from the top left to bottom right of the region. These elements can have semi-conductive properties. The non-metals include basic elements such as carbon, oxygen and nitrogen, which include a large portion of the elements common in biology. The second to last column are the halogens, which are highly reactive in their elemental forms and produce anionic ions. The final column of the table contains the noble gases, which are almost non-reactive and are all gaseous elements under standard conditions.
A region at the bottom of the periodic table showcases the actinides and lanthanides, which correspond to the filling of the f orbitals. Many of these elements are rare and radioactive, and some are not found in nature.