The main group elements of the periodic table are groups 1, 2 and 13 through 18. Elements in these groups are collectively known as main group or representative elements. These groups contain the most naturally abundant elements, comprise 80 percent of the earth"s crust and are the most important for life. Economically the most produced chemicals are main group elements or their compounds. It is in the main group elements that we most clearly see the trends in physical and chemical properties of the elements that chemists have used to understand the "stuff" things are made of.

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Contents


1 Group 1 (Alkali Metals)2 Group 2 (Alkaline Earth Metals)3 Group 13 (Boron Group)4 Group 14 (Carbon Group)5 Group 15 (Nitrogen Group)6 Group 16 (Chalcogens)7 Group 17 (Halogens)8 Group 18 (Noble Gases)

Group 1 (Alkali Metals)

The alkali metals are the series of elements in Group 1 of the periodic table (excluding hydrogen in all but one rare circumstance). The series consists of the elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).

Properties

The alkali metals are silver-colored (caesium has a golden tinge), soft, low-density metals. These elements all have one valence electron which is easily lost to form an ion with a single positive charge. They have the lowest ionization energies in their respective periods. This makes them very reactive and they are the most active metals. Due to their activity they occur naturally in ionic compounds not in their elemental state.

Group1Period234567
3 Li 
11 Na 
19 K 
37 Rb 
55 Cs 
87 Fr 

The alkali metals react readily with halogens to form ionic salts, such as table salt, sodium chloride (NaCl). They are famous for their vigorous reactions with water to liberate hydrogen gas. These reactions also often liberate sufficient energy to ignite the hydrogen and can be quite dangerous. As we move down the group the reactions become increasingly violent. The reaction with water is as follows:

Alkali metal + water → Alkali metal hydroxide + hydrogen

With potassium as an example:

2K(s)+2H2O(l) →2KOH(aq)+H2(g)displaystyle 2K_(s)+2H_2O_(l) o 2KOH_(aq)+H_2_(g)
*

The oxides, hydrides, and hydoxides of these metals are basic (alkaline). In particular the hydoxides resulting from the reaction with water are our most common laboratory bases (alkalis). It is from this character that they derive their group name.

Hydrogen also has a single valence electron and is usually placed at the top of Group 1, but it is not a metal (except under extreme circumstances as metallic hydrogen); rather it exists naturally as a diatomic gas. Hydrogen can form ions with a single positive charge, but removal of its single electron requires considerably more energy than removal of the outer electron from the alkali metals. Unlike the alkali metals hydrogen atoms can also gain an electron to form the negatively charged hydride ion. The hydride ion is an extremely strong base and does not usually occur except when combined with the alkali metals and some transition metals (i.e. the ionic sodium hydride, NaH). In compounds hydrogen most often forms covalent bonds.

Under extremely high pressure, such as is found at the core of Jupiter, hydrogen does become metallic and behaves like an alkali metal; see metallic hydrogen.

Group 2 (Alkaline Earth Metals)

Group2
Period
24Be
312Mg
420Ca
538Sr
656Ba
788Ra

The alkaline earth metals are the series of elements in Group 2 of the periodic table. The series consists of the elements beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra) (though radium is not always considered an alkaline on earth due to its radioactivity).

Properties

The alkaline earth metals are silvery colored, soft, low-density metals, though are a bit harder than the alkali metals. These elements all have two valence electrons and tend to lose both to form ions with a two plus charge. Berylium is the least metallic element in the group and tends form covalent bonds in its compounds.

These metals are less active than the alkali metals, but are still fairly active. They react readily with halogens to form ionic salts, and can react slowly with water. Magnesium reacts only with steam and calcium with hot water. Beryllium is an exception: It does not react with water or steam, and its halides are covalent. The oxides are basic and dissolve in acids and the hydroxides are strong bases, though not as soluable as the alkali metal hydroxides.

The alkaline earth metals are named after their oxides, the alkaline earths, whose old-fashioned names were beryllia, magnesia, lime, strontia and baryta. These were named alkaline earths because of their intermediate nature between the alkalis (oxides of the alkali metals) and the rare earths (oxides of rare earth metals). The classification of some apparently inert substances as "earths" is millennia old. The earliest known system used by the Greeks consisted of four elements, including earth. Later alchemists applied the term to any solid substance that did not melt and was not changed by fire. The realization that "earths" were not elements but compounds is attributed to the chemist Antoine Lavoisier. In his Traité Élémentaire de Chimie (“Elements of Chemistry”) of 1789 he called them Substances simples salifiables terreuses, or salt-forming earth elements. Later, he suggested that the alkaline earths might be metal oxides, but admitted that this was mere conjecture. In 1808, acting on Lavoisier"s idea, Humphry Davy became the first to obtain samples of the metals by electrolysis of their molten earths.

Group 13 (Boron Group)

Group13Period234567
5B
13Al
31Ga
49In
81Tl
113Uut

The Boron group is the series of elements in group 13 (formerly group III) in the periodic table. It consists of the elements boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl), and ununtrium (Uut) (unconfirmed).

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Properties

In this group we begin to see the changeover toward non-metallic character. First appearing at the top of the group. Boron is a metalloid, it has characteristics intermediate between metals and non-metals, and the rest of the group are metals. These elements are characterized by having three valence electrons. The metals can loose all three electrons to form ions with a three plus charge in ionic compounds, but boron tends to form covalent bonds. The oxides of the metals dissolve in acids so may be considered basic, but aluminum oxide also dissolves in bases. It is amphoteric; that is, it displays both acidic and basic characteristics. This is another indication of the changeover to non-metallic character. Aluminum is the third most abundant element in the earth"s crust (7.4 percent), and is widely used in packaging materials. Aluminum is an active metal, but the stable oxide forms a protective coating over the metal making resistant to corrosion.