Periodic table, main group elements
The main groups 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
Group I
| Group | 1 |
|---|---|
| Period | |
| 2 | 3 Li |
| 3 | 11 Na |
| 4 | 19 K |
| 5 | 37 Rb |
| 6 | 55 Cs |
| 7 | 87 Fr |
The alkali metals are the series of elements in Group 1 (IUPAC style) of the periodic table (excluding hydrogen in all but one rare circumstance): lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). They are all highly reactive and are never found in elemental form in nature. As a result they are stored under oil.
Introduction
The alkali metals are silver-colored (caesium has a golden tinge), soft, low-density metals, which react readily with halogens to form ionic salts, and with water to form strongly alkaline (basic) hydroxides. These elements all have one electron in their outermost shell, so the energetically preferred state of achieving a filled electron shell is to lose one electron to form a singly charged positive ion.
Hydrogen, with a solitary electron, is sometimes placed at the top of Group 1, but it is not an alkali metal (except under extreme circumstances as metallic hydrogen); rather it exists naturally as a diatomic gas. Removal of its single electron requires considerably more energy than removal of the outer electron for the alkali metals. As in the halogens, only one additional electron is required to fill in the outermost shell of the hydrogen atom, so hydrogen can in some circumstances behave like a halogen, forming the negative hydride ion. Binary compounds of hydride with the alkali metals and some transition metals have been prepared.
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.
Alkali metals are highly reactive. They have the lowest ionization potentials in their respective periods, as removing the single electron from the outermost shell gives them the stable inert gas configuration. But their second ionization potentials are very high, as removing an electron from a species having a noble gas configuration is very difficult.
Reactions in water
Alkali metals are famous for their vigourous reactions with water, and these reactions become increasingly violent as you move down the periods. The reaction with water is as follows:
Alkali metal + water → Alkali metal hydroxide + hydrogen
With potassium as an example:
In this reaction, enough energy is produced to ignite the hydrogen, creating a lilac flame above the potassium
Explanation of above periodic table slice
| Alkali metals | atomic number in black are solids | solid borders are primordial elements (older than the Earth) | dashed borders are naturally radioactive elements with no isotopes older than the Earth |
See also
External
- Science aid:Alkali metals A simple look at alkali metals
- Doc Brown, Alkali metals
Wiki
Group 2
| Group | 2 |
|---|---|
| Period | |
| 2 | 4 Be |
| 3 | 12 Mg |
| 4 | 20 Ca |
| 5 | 38 Sr |
| 6 | 56 Ba |
| 7 | 88 Ra |
The alkaline earth metals are the series of elements in Group 2 (IUPAC style) of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra) (though radium is not always considered an alkaline earth due to its radioactivity).
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 ancient Greeks consisted of four elements, including earth. This system was later refined by philosophers and alchemists such as Aristotle (4th century B.C.E.), Paracelsus (first half of 16th century), John Becher (mid 17th century) and Georg Stahl (late 17th century), with later thinkers subdividing 'earth' into three or more types. 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.
The alkaline earth metals are silvery colored, soft, low-density metals, which react readily with halogens to form ionic salts, and with water, though not as rapidly as the alkali metals, to form strongly alkaline (basic) hydroxides. Beryllium is an exception: It does not react with water or steam, and its halides are covalent. For example, where sodium and potassium react with water at room temperature, magnesium reacts only with steam and calcium with hot water. These elements all have two electrons in their outermost shell, so the energetically preferred state of achieving a filled electron shell is to lose two electrons to form doubly charged positive ions.
| Alkaline earth metals | atomic number in black are solids | solid borders are primordial elements (older than the Earth) | dashed borders are naturally radioactive elements with no isotopes older than the Earth |
Group 13
| Group | 13 |
|---|---|
| Period | |
| 2 | 5 B |
| 3 | 13 Al |
| 4 | 31 Ga |
| 5 | 49 In |
| 6 | 81 Tl |
| 7 | 113 Uut |
The Boron group is the series of elements in group 13 (IUPAC style) in the periodic table. These elements are characterized by having three electrons in their outer energy levels (valence layers). Boron is considered a metalloid, and the rest are considered metals of the poor metals group.
The boron group consists of boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl), and ununtrium (Uut) (unconfirmed).
Boron occurs sparsely probably because of disruption of its nucleus by bombardment with subatomic particles produced from natural radioactivity. Aluminum occurs widely on earth and in fact, it is the third most abundant element in the earth's crust (7.4%).
| Metalloids | Poor metals | atomic number in black are solids | solid borders are primordial elements (older than the Earth) | dotted borders are radioactive, synthetic elements |
|---|
Group 14
| Group | 14 |
|---|---|
| Period | |
| 2 | 6 C |
| 3 | 14 Si |
| 4 | 32 Ge |
| 5 | 50 Sn |
| 6 | 82 Pb |
| 7 | 114 Uuq |
The carbon group is group 14 (IUPAC style) in the periodic table. In schools, it is often known as group 4.
Each element in this group has 4 electrons in its outer energy level. In most cases, the elements share their electrons. The tendency to lose electrons increases as the size of the atom increases, as it does with increasing atomic number. Carbon alone forms negative ions, in the form of carbide (C4-) ions. Silicon and germanium, both metalloids, each can form +4 ions.
The group consists of carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and ununquadium (Uuq).
| Nonmetals | Metalloids | Poor metals | atomic number in black are solids | solid borders are primordial elements (older than the Earth) | dotted borders are radioactive, synthetic elements |
|---|
Group 15
| Group | 15 |
|---|---|
| Period | |
| 2 | 7 N |
| 3 | 15 P |
| 4 | 33 As |
| 5 | 51 Sb |
| 6 | 84 Bi |
| 7 | 115 Uup |
The Nitrogen group elements (a.k.a. group VA) are also known as IUPAC Group 15 (formerly Group V) of the periodic table.
This group has the defining characteristic that all the component elements have 5 electrons in their outermost shell, that is 2 electrons in the s subshell and 3 in the p subshell. They are therefore 3 electrons short of filling their outermost electron shell in their non-ionized state. The most important element of this group is Nitrogen (N), which in its diatomic form is the principal component of air.
Other members of the group include Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi) and ununpentium (UUp) (unconfirmed).
The collective name pnicogens (now also spelled pnictogens) is also sometimes used for elements of this group, with binary compounds being called pnictides: neither term is approved by IUPAC. Both spellings are said to derive from the Greek πνίγειν (pnigein), to choke or stifle, which is a property of nitrogen.
| Nonmetals | Metalloids | Poor metals | atomic number in black are solids | solid borders are primordial elements (older than the Earth) | dotted borders are radioactive, synthetic elements |
|---|
Group 16
| Group | 16 |
|---|---|
| Period | |
| 2 | 8 O |
| 3 | 16 S |
| 4 | 34 Se |
| 5 | 52 Te |
| 6 | 84 Po |
| 7 | 116 Uuh |
The chalcogens (with the "ch" pronounced with a hard "c" as in "chemistry") are the name for the periodic table group 16 (old-style: VIB or VIA) in the periodic table. It is sometimes known as the oxygen family. It consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), the radioactive polonium (Po), and the synthetic ununhexium (Uuh). The compounds of the heavier chalcogens (particularly the sulfides, selenides, and tellurides) are collectively known as chalcogenides. Unless grouped with a heavier chalcogen, oxides are not considered chalcogenides.
The name is generally considered to mean "ore former" from the Greek chalcos "ore" and -gen "formation". [1]
Oxygen and sulfur are nonmetals, and polonium, selenium and tellurium are metalloid semiconductors (i.e., their electrical properties are between those of a metal and an insulator). Nevertheless, tellurium, as well as selenium, is often referred to as a metal when in elemental form.
Chalcogenides are quite common as minerals. For example, FeS2 (pyrite) is an iron ore and AuTe2 gave its name to the gold rush town of Telluride, Colorado in the United States.
The formal oxidation number of the chalcogen is generally -2 in a chalcogenide but other values (e.g. -1 in pyrite) can be attained.
The highest formal oxidation number +6 is found in sulfates, selenates and tellurates, e.g. in Na2SeO4 (sodium selenate). Modern chemical understanding based on quantum theory somewhat outdates the use of formal oxidation numbers in favour of a many-electron wavefunction approach allowing detailed computer simulation, though the concept, while flawed, is still useful in thought experiments.
| Nonmetals | Metalloids | Poor metals | atomic number in red are gases | atomic number in black are solids | solid borders are primordial elements (older than the Earth) | dashed borders are naturally radioactive elements | dotted borders are radioactive, synthetic elements |
|---|
See also
- Gold chalcogenides
- Periodic table
External links
Group 17
- This article discusses the group of chemical elements in the periodic table:for the light bulb, see the halogen lamp.
| Group | 17 |
|---|---|
| Period | |
| 2 | 9 F |
| 3 | 17 Cl |
| 4 | 35 Br |
| 5 | 53 I |
| 6 | 85 At |
| 7 | 117 Uus |
The halogens are a chemical series. They are the elements in Group 17 (old-style: VII or VIIA) of the periodic table: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At) and the as yet undiscovered ununseptium (Uus). The term halogen was coined to mean elements which produce salt in union with a metal. It comes from 18th century scientific French nomenclature based on erring adaptations of Greek roots.
These elements are diatomic molecules in their natural form. They require one more electron to fill their outer electron shells, and so have a tendency to form a singly-charged negative ion. This negative ion is referred to as a halide ion; salts containing these ions are known as halides.
Halogens are highly reactive, and as such can be harmful or lethal to biological organisms in sufficient quantities. Chlorine and iodine are both used as disinfectants for such things as drinking water, swimming pools, fresh wounds, dishes, and surfaces. They kill bacteria and other potentially harmful microorganisms, a process known as sterilization. Their reactive properties are also put to use in bleaching. Chlorine is the active ingredient of most fabric bleaches and is used in the production of most paper products.
Halide ions combined with single hydrogen atoms form the hydrohalic acids (i.e., HF, HCl, HBr, HI), a series of particularly strong acids. (HAt, or "hydrastatic acid", should also qualify, but it is not typically included in discussions of hydrohalic acid due to astatine's extreme instability toward alpha decay.)
They react with each other to form interhalogen compounds. Diatomic interhalogen compounds (BrF, ICl, ClF, etc.) bear strong superficial resemblance to the pure halogens.
Many synthetic organic compounds such as plastic polymers, and a few natural ones, contain halogen atoms; these are known as halogenated compounds or organic halides. Chlorine is by far the most abundant of the halogens, and the only one needed in relatively large amounts (as chloride ions) by humans. For example, chloride ions play a key role in brain function by mediating the action of the inhibitory transmitter GABA and are also used by the body to produce stomach acid. Iodine is needed in trace amounts for the production of thyroid hormones such as thyroxine. On the other hand, neither fluorine nor bromine are believed to be really essential for humans, although small amounts of fluoride can make tooth enamel resistant to decay.
They show a number of trends when moving down the group - for instance, decreasing electronegativity and reactivity, increasing melting and boiling point.
| Halogen | Atomic Mass (u) | Melting Point (K) | Boiling Point (K) | Electronegativity (Pauling) |
| Fluorine | 18.998 | 53.53 | 85.03 | 3.98 |
| Chlorine | 35.453 | 171.6 | 239.11 | 3.16 |
| Bromine | 79.904 | 265.8 | 332.0 | 2.96 |
| Iodine | 126.904 | 386.85 | 457.4 | 2.66 |
| Astatine | (210) | 575 | 610 ? | 2.2 |
| Ununseptium | (291)* | * | * | * |
* Ununseptium has not yet been discovered; values are either unknown if no value appears, or are estimates based on other similar chemicals.
| Halogens | atomic number in red are gases | atomic number in green are liquids | atomic number in black are solids |
|---|---|---|---|
| solid borders are primordial elements (older than the Earth) | dashed borders are naturally radioactive elements | dotted borders are radioactive, synthetic elements | those without borders have not been discovered yet |
See also
- pseudohalogen
Group 18
| Group | 18 |
|---|---|
| Period | |
| 1 | 2 He |
| 2 | 10 Ne |
| 3 | 18 Ar |
| 4 | 36 Kr |
| 5 | 54 Xe |
| 6 | 86 Rn |
| 7 | 118 Uuo |
The noble gases are the chemical elements in group 18 (old-style Group 0) of the periodic table. This chemical series contains helium, neon, argon, krypton, xenon, and radon.
Etymology
The noble gases were previously referred to as inert gases, but this term is not strictly accurate because several of them do take part in chemical reactions. Another older term was rare gases, although in fact argon forms a considerable part (0.93% by volume, 1.29% by mass) of the Earth's atmosphere.
The name 'noble gases' is an allusion to the similarly unreactive Noble metals, so called due to their preciousness, resistance to corrosion and long association with the aristocracy.
| Noble gases | atomic number in red are gases | solid borders are primordial elements (older than the Earth) | dashed borders are naturally radioactive elements | dotted borders are radioactive, synthetic elements | those without borders have not been discovered yet |
|---|
Chemistry
The general physical properties of Noble gases are:
They are all monatomic molecules and chemically inert (unreactive), except for Kr and Xe, which have shown some reactivity in the laboratory—see noble gas compounds.
The noble gases' lack of reactivity is due to their having a complete valence shell. They have little tendency to gain or lose electrons. The noble gases have high ionization energies and negligible electronegativities. The noble gases have low boiling points and are all gases at room temperature.
Because of their unreactivity, the noble gases were not discovered until 1868, when helium was detected spectrographically in the Sun. The isolation of helium on Earth had to wait until 1895. The noble gases have very weak inter-atomic forces of attraction, and consequently very low melting points and boiling points. This is why they are all gases under normal conditions, even those with larger atomic masses than many normally solid elements.
Ununoctium
No isotopes with 118 protons have yet been detected in nature or synthesized in the laboratory. In the meantime, the systematic name "ununoctium" is used to refer to this hypothetical element. If discovered, ununoctium is expected to be another noble gas, filling the empty space in the periodic table beneath radon. All its isotopes are likely to be radioactive with a very short half-life in the millisecond range.
Applications
One of the most commonly encountered uses of the noble gases in everyday life is in lighting. Argon is often used as a suitable safe and inert atmosphere for the inside of filament light bulbs. Some of the noble gases glow distinctive colours when used inside lighting tubes (neon lights). Helium, due to its unreactivity (compared to flammable hydrogen) and lightness, is often used in blimps and balloons.
Physical Properties
| Property | |||||||
| Element Number | 2 | 10 | 18 | 36 | 54 | 86 | 118 |
| Element Name | Helium | Neon | Argon | Krypton | Xenon | Radon | Ununoctium |
| Normal Density | 0.1786 | 0.9002 | 1.7818 | 3.708 | 5.851 | 9.97 | N/A |
| Atomic Mass | 4.00 | 20.2 | 39.9 | 82.92 | 130.2 | 222.4 | N/A |
| Boiling Pt. (°C) | -268.83 | -245.92 | -185.81 | -151.7 | -106.6 | -62 | N/A |
| Melting Pt. (°C) | -272 | -248.52 | -189.6 | -157 | -111.5 | -71 | N/A |
External links
- Ohio State University press release for uranium compounds with noble gases.
- Rare Gases - Neon, Krypton, Xenon Properties, Uses, Applications
- Argon Ar Properties, Uses, Applications
- Science Aid: Noble gases Simple look at the properties and uses of noble gases
Credits
New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:
- Alkali_metal history
- Alkaline_earth_metal history
- Boron_group history
- Carbon_group history
- Nitrogen_group history
- Chalcogen history
- Halogen history
- Noble_gas history
The history of this article since it was imported to New World Encyclopedia:
Note: Some restrictions may apply to use of individual images which are separately licensed.
