The timeless Periodic Table organizes the chemical aspects according to the number of proloads that each has in its atomic nucleus.(Image credit: Karl Tate, steustatiushistory.org contributor)
In the late 1nine century, Russian chemist Dmitri Mendeleev publimelted his initially attempt at grouping chemical elements according to their atomic weights. There were only about 60 aspects well-known at the moment, yet Mendeleev realized that when the aspects were arranged by weight, specific types of facets developed in regular intervals, or periods.

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Today, 150 years later, chemists officially recognize 118 aspects (after the addition of four newcomers in 2016) and also still usage Mendeleev"s routine table of facets to organize them. The table starts via the simplest atom, hydrogen, and then organizes the remainder of the elements by atomic number, which is the number of prolots each consists of. With a handful of exceptions, the order of the aspects synchronizes via the increasing mass of each atom.

The table has salso rows and also 18 columns. Each row represents one period; the duration variety of an element suggests exactly how many type of of its power levels house electrons. Sodium, for circumstances, sits in the 3rd period, which indicates a sodium atom frequently has electrons in the first three energy levels. Moving dvery own the table, periods are longer bereason it takes more electrons to fill the larger and also even more complex outer levels.


The columns of the table recurrent teams, or households, of aspects. The elements in a group regularly look and behave similarly, because they have actually the same variety of electrons in their outermany shell — the confront they present to the civilization. Group 18 aspects, on the far ideal side of the table, for instance, have completely full outer shells and also rarely take part in chemical reactions.


Elements are typically classified as either a steel or nonmetal, yet the separating line in between the 2 is fuzzy. Metal elements are generally good conductors of electricity and warm. The subteams within the metals are based on the equivalent features and chemical properties of these collections. Our description of the periodic table uses commonly welcomed groupings of elements, according to the Los Alamos National Laboratory.


Alkali metals: The alkali steels make up the majority of of Group 1, the table"s first column. Shiny and also soft enough to reduced through a knife, these steels start with lithium (Li) and also finish with francium (Fr). They are additionally incredibly reactive and will burst right into flame or also explode on contact via water, so chemists keep them in oils or inert gases. Hydrogen, through its single electron, also resides in Group 1, yet the gas is thought about a nonmetal.

Alkaline-earth metals: The alkaline-earth metals comprise Group 2 of the periodic table, from beryllium (Be) through radium (Ra). Each of these facets has actually two electrons in its outermost power level, which renders the alkaline earths reenergetic sufficient that they"re rarely uncovered alone in nature. But they"re not as reactive as the alkali steels. Their chemical reactions typically take place more gradually and also develop much less heat compared to the alkali metals.

Lanthanides: The 3rd group is much also lengthy to fit into the third column, so it is damaged out and also flipped sideways to become the height row of the island also that floats at the bottom of the table. This is the lanthanides, elements 57 via 71 — lanthanum (La) to lutetium (Lu). The aspects in this group have a silexceptionally white color and also tarnish on contact via air.


Actinides: The actinides line the bottom row of the island and also consist of facets 89, actinium (Ac), via 103, lawrencium (Lr). Of these elements, only thorium (Th) and uranium (U) occur normally on Earth in extensive amounts. All are radioenergetic. The actinides and the lanthanides together develop a group dubbed the inner shift metals.

Transition metals: Returning to the primary body of the table, the remainder of Groups 3 via 12 recurrent the remainder of the change metals. Hard but malleable, shiny, and also possessing excellent conductivity, these elements are what you typically think of once you hear the word steel. Many kind of of the best hits of the steel world — consisting of gold, silver, iron and platinum — live right here.

Post-change metals: Ahead of the jump into the nonsteel people, mutual characteristics aren"t neatly split along vertical team lines. The post-transition steels are aluminum (Al), gallium (Ga), indium (In), thallium (Tl), tin (Sn), lead (Pb) and bismuth (Bi), and also they expectations Group 13 to Group 17. These elements have actually some of the classical characteristics of the transition steels, but they tfinish to be softer and also conduct more poorly than other transition metals. Many kind of periodic tables will attribute a bolded "staircase" line below the diagonal connecting boron with astatine. The post-transition metals cluster to the lower left of this line.

Metalloids: The metalloids are boron (B), silsymbol (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po). They create the stairsituation that represents the steady change from steels to nonmetals. These facets occasionally behave actually as semiconductors (B, Si, Ge) fairly than as conductors. Metalloids are also called "semimetals" or "negative steels."

Nonmetals: Everything else to the upper appropriate of the staircase — plus hydrogen (H), stranded means earlier in Group 1 — is a nonsteel. These include carbon (C), nitrogen (N), phosphorus (P), oxygen (O), sulfur (S) and selenium (Se).

Halogens: The peak four aspects of Group 17, from fluorine (F) through astatine (At), represent among two subsets of the nonsteels. The halogens are rather chemically reactive and tend to pair up with alkali steels to create assorted types of salt. The table salt in your kitchen, for instance, is a marital relationship between the alkali steel sodium and the halogen chlorine.

Noble gases: Colorless, odormuch less and practically completely nonreenergetic, the inert, or noble gases round out the table in Group 18. Many type of chemists mean oganesboy, one of the 4 freshly named elements, to share these characteristics; but, because this aspect has a half-life measuring in the milliseconds, no one has actually been able to test it directly. Oganesson completes the seventh duration of the periodic table, so if anyone maneras to synthesize aspect 119 (and the race to execute so is already underway), it will certainly loop around to begin row eight in the alkali steel column.

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Due to the fact that of the cyclical nature created by the periodicity that offers the table its name, some chemists favor to visualize Mendeleev"s table as a circle.