Regions Of The Periodic Table

How the Periodic Tabular array of the Elements is arranged

The classic Periodic Table organizes the chemical elements according to the number of protons that each has in its atomic nucleus. (Image credit: Karl Tate, Livescience.com contributor)

Scientists had a rudimentary understanding of the periodic tabular array of the elements centuries ago. But in the tardily 19th century, Russian chemist Dmitri Mendeleev published his outset attempt at grouping chemical elements according to their atomic weights. In that location were only virtually 60 elements known at the time, but Mendeleev realized that when the elements were organized by weight, certain types of elements occurred in regular intervals, or periods.

Today, 150 years after, chemists officially recognize 118 elements (after the addition of 4 newcomers in 2016) and withal use Mendeleev'south periodic table of elements to organize them. The table starts with the simplest atom, hydrogen, and so organizes the rest of the elements by atomic number, which is the number of protons each contains. With a handful of exceptions, the guild of the elements corresponds with the increasing mass of each atom.

The table has seven rows and 18 columns. Each row represents ane period; the flow number of an element indicates how many of its energy levels house electrons. Sodium, for case, sits in the third period, which means a sodium cantlet typically has electrons in the kickoff 3 energy levels. Moving downwardly the table, periods are longer because it takes more electrons to make full the larger and more than circuitous outer levels.

The columns of the table represent groups, or families, of elements. The elements in a grouping often look and behave similarly, because they take the aforementioned number of electrons in their outermost trounce — the face they show to the world. Group 18 elements, on the far right side of the table, for example, have completely full outer shells and rarely participate in chemic reactions.

Elements are typically classified as either a metallic or nonmetal, but the dividing line between the 2 is fuzzy. Metal elements are usually good conductors of electricity and heat. The subgroups within the metals are based on the like characteristics and chemical properties of these collections. Our description of the periodic table uses commonly accustomed groupings of elements, according to the Los Alamos National Laboratory (opens in new tab).

The periodic table of elements is arranged into several broad groups (Image credit: Future)

Groups of the Periodic table

Alkali metals: The alkali metals make up nearly of Grouping 1, the table's first cavalcade. Shiny and soft enough to cut with a knife, these metals first with lithium (Li) and end with francium (Fr). They are also extremely reactive and will burst into flame or even explode on contact with water, so chemists shop them in oils or inert gases. Hydrogen, with its single electron, also lives in Group ane, but the gas is considered a nonmetal.

Alkaline metal-world metals: The alkaline-earth metals make upward Group ii of the periodic table, from beryllium (Be) through radium (Ra). Each of these elements has two electrons in its outermost energy level, which makes the alkaline earths reactive enough that they're rarely found alone in nature. Just they're not every bit reactive as the brine metals. Their chemical reactions typically occur more slowly and produce less heat compared to the alkali metals.

Lanthanides: The third group is much as well long to fit into the third column, so it is broken out and flipped sideways to become the height row of the island that floats at the bottom of the table. This is the lanthanides, elements 57 through 71 — lanthanum (La) to lutetium (Lu). The elements in this group accept a silverish white color and tarnish on contact with air.

Actinides: The actinides line the bottom row of the island and incorporate elements 89, actinium (Ac), through 103, lawrencium (Lr). Of these elements, only thorium (Th) and uranium (U) occur naturally on Earth in substantial amounts. All are radioactive. The actinides and the lanthanides together form a group called the inner transition metals.

Transition metals: Returning to the main trunk of the table, the rest of Groups iii through 12 stand for the rest of the transition metals. Hard but malleable, shiny, and possessing skillful electrical conductivity, these elements are what you typically recall of when you hear the word metal. Many of the greatest hits of the metal globe — including golden, silver, iron and platinum — live here.

Post-transition metals: Ahead of the leap into the nonmetal earth, shared characteristics aren't neatly divided along vertical group lines. The post-transition metals are aluminum (Al), gallium (Ga), indium (In), thallium (Tl), tin (Sn), lead (Pb) and bismuth (Bi), and they span Grouping 13 to Grouping 17. These elements have some of the classic characteristics of the transition metals, but they tend to be softer and bear more than poorly than other transition metals. Many periodic tables will feature a bolded "staircase" line below the diagonal connecting boron with astatine. The mail-transition metals cluster to the lower left of this line.

Metalloids: The metalloids are boron (B), silicon (Si), germanium (Ge), arsenic (Every bit), antimony (Sb), tellurium (Te) and polonium (Po). They form the staircase that represents the gradual transition from metals to nonmetals. These elements sometimes behave as semiconductors (B, Si, Ge) rather than every bit conductors. Metalloids are also chosen "semimetals" or "poor metals."

Nonmetals: Everything else to the upper right of the staircase — plus hydrogen (H), stranded manner back in Group 1 — is a nonmetal. These include carbon (C), nitrogen (North), phosphorus (P), oxygen (O), sulfur (S) and selenium (Se).

Halogens: The elevation 4 elements of Group 17, from fluorine (F) through astatine (At), stand for one of two subsets of the nonmetals. The halogens are quite chemically reactive and tend to pair upwards with alkali metals to produce diverse types of salt. The table common salt in your kitchen, for instance, is a wedlock between the alkali metal sodium and the halogen chlorine.

Noble gases: Colorless, odorless and near completely nonreactive, the inert, or noble gases round out the table in Group 18. Many chemists expect oganesson (previously designated "ununoctium"), one of the 4 newly named elements, to share these characteristics; however, because this element has a one-half-life measuring in the milliseconds, no i has been able to test information technology directly. Oganesson completes the seventh period of the periodic table, so if anyone manages to synthesize element 119 (and the race to exercise so is already underway), it will loop around to kickoff row viii in the alkali metal column.

Considering of the cyclical nature created by the periodicity that gives the tabular array its name, some chemists prefer to visualize Mendeleev'southward tabular array every bit a circumvolve.

Additional resources:

Watch this brief video about the periodic table and element groups, from Crash Grade (opens in new tab).
Flip through this interactive periodic tabular array of elements at ptable.com (opens in new tab).
Check out this free, online educational resource for understanding elemental groups from CK-12 (opens in new tab).

Ben Biggs is a keen and experienced scientific discipline and technology writer, published book author, and editor of the accolade-winning magazine, How It Works. He has also spent many years writing and editing for technology and video games outlets, afterward becoming the editor of All Virtually Space then, Existent Crime mag.