The eight main groups – for your AI tutor

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Context: the page “The eight main groups”

All eight main groups with all their elements. The main group tells how many electrons are in the outer shell.

Why

Elements in one group behave in a similar way. If you know the main group, you can predict how an element behaves.

Explore the elements

Every colour is a main group. Tap an element to find out how its atoms are built, which compounds it forms and what it is used for.

Interactive: I · Alkali metals (and hydrogen): Shiny silvery, reactive metals with one outer electron that they give away easily. Hydrogen is in this group too, but it is not an alkali metal. - Hydrogen (H), Atomic number 1, Main group I, Period 1, non-metal. Electrons per shell: 1. Common compounds: H₂O (Water: covers most of our planet's surface); CH₄ (Methane: an important part of natural gas); NH₃ (Ammonia: made from hydrogen and nitrogen, a starting material for fertiliser). Uses: Rocket fuel, and used in welding; Hardens plant oil, which is how margarine is made; Lifting gas for weather balloons because it is so light. Did you know? Hydrogen is the most common element in the whole universe. - Lithium (Li), Atomic number 3, Main group I, Period 2, metal. Electrons per shell: 2, 1. Common compounds: Li₂CO₃ (Lithium carbonate: the most important lithium compound, also used in making glass); LiCl (Lithium chloride: absorbs moisture and is used to dry gases); LiOH (Lithium hydroxide: used for greases and to clean the air in submarines). Uses: Rechargeable batteries in phones, laptops and electric cars; Non-rechargeable lithium batteries; Lightweight alloys for aircraft and spacecraft. Did you know? Lithium is the lightest solid element at room temperature. - Sodium (Na), Atomic number 11, Main group I, Period 3, metal. Electrons per shell: 2, 8, 1. Common compounds: NaCl (Table salt: seasons food and preserves it); NaOH (Sodium hydroxide: its solution, caustic soda, is used for soap and dyes); NaHCO₃ (Baking soda: used as baking powder). Uses: Cooling the valves of combustion engines; Sodium vapour lamps gave yellow light for streets; Coolant in fast breeder nuclear reactors. Did you know? Buna, the first artificial rubber, was named after butadiene and sodium. - Potassium (K), Atomic number 19, Main group I, Period 4, metal. Electrons per shell: 2, 8, 8, 1. Common compounds: KCl (Potassium chloride: potash fertiliser and a source of many other potassium compounds); KNO₃ (Potassium nitrate: the main ingredient of black powder); K₂SO₄ (Potassium sulfate: mainly used as a fertiliser). Uses: Coolant in some nuclear reactors (mixed with sodium); Added to tungsten wire for light-bulb filaments. The metal potassium has little technical importance, so only two uses are listed. Did you know? Potassium has even been detected in the atmospheres of distant planets. - Rubidium (Rb), Atomic number 37, Main group I, Period 5, metal. Electrons per shell: 2, 8, 18, 8, 1. Common compounds: RbCl (Rubidium chloride: a salt from which the metal can be made); RbOH (Rubidium hydroxide: formed when rubidium reacts violently with water); RbAlSi₃O₈ (Rubicline: a very rare mineral, found on the island of Elba in 1998). Uses: Rubidium clocks: atomic clocks in navigation satellites such as GPS; In research, for cooling atoms with laser light. Did you know? The name means “deep red”, after two dark red lines in the light the element gives off. - Caesium (Cs), Atomic number 55, Main group I, Period 6, metal. Electrons per shell: 2, 8, 18, 18, 8, 1. Common compounds: CsCl (Caesium chloride: used to separate and purify DNA in an ultracentrifuge); CsI (Caesium iodide: a transparent material in scintillation counters); CsNO₃ (Caesium nitrate: used in military flares and smoke screens). Uses: Timekeeper in atomic clocks that set world time; Propellant in ion thrusters for spaceflight; Binds leftover gases in vacuum tubes and so improves the vacuum. Did you know? Since 1967, the second has been defined using caesium atoms. - Francium (Fr), Atomic number 87, Main group I, Period 7, metal. Electrons per shell: 2, 8, 18, 32, 18, 8, 1. Uses: Used in basic research to study the structure of atoms. Francium is extremely rare and decays within minutes, so no compounds and only one use are listed. Did you know? The whole Earth's crust contains only about 28 grams of francium. II · Alkaline earth metals: Shiny, reactive metals with two outer electrons. Radium is radioactive. - Beryllium (Be), Atomic number 4, Main group II, Period 2, metal. Electrons per shell: 2, 2. Common compounds: BeO (Beryllium oxide: a ceramic that conducts heat well but insulates electricity); Be(OH)₂ (Beryllium hydroxide: the main beryllium compound, a step toward making the metal). Uses: Added to copper to make hard, springy beryllium copper; Mirrors for space telescopes, because it is so light; Windows in X-ray tubes, since X-rays pass through it. Beryllium and its compounds are toxic and are used in only a few applications. Did you know? Of all elements lighter than iron, beryllium is the rarest. - Magnesium (Mg), Atomic number 12, Main group II, Period 3, metal. Electrons per shell: 2, 8, 2. Common compounds: MgO (Magnesium oxide: withstands great heat, so it is used for ceramics in labs and industry); MgCO₃ (Magnesium carbonate: the gym chalk that keeps gymnasts' hands dry); MgSO₄ (Magnesium sulfate: known as Epsom salt, occurs as the mineral epsomite). Uses: Light alloys for cars and aircraft; Protects other metals from corrosion by corroding in their place; Fire starter: magnesium shavings ignite easily. Did you know? Magnesium can burn even underwater: there are torches that work there. - Calcium (Ca), Atomic number 20, Main group II, Period 4, metal. Electrons per shell: 2, 8, 8, 2. Common compounds: CaCO₃ (Calcium carbonate: the main substance of limestone, chalk and marble); CaSO₄ (Calcium sulfate: occurs as gypsum and is used as a building material); CaO (Calcium oxide: quicklime, used to make mortar and plaster). Uses: Used in metallurgy to produce other metals such as vanadium and zirconium; Added to alloys, for example with aluminium or copper. The metal calcium is mostly used in its compounds, so only two uses of the element are listed. Did you know? Calcium is not only in bones: it also helps nerves and muscles pass on signals. - Strontium (Sr), Atomic number 38, Main group II, Period 5, metal. Electrons per shell: 2, 8, 18, 8, 2. Common compounds: SrCO₃ (Strontium carbonate: the most important commercial form, used for magnets among other things); Sr(NO₃)₂ (Strontium nitrate: gives fireworks their red colour); SrSO₄ (Celestine (strontium sulfate): an important ore, also used in drilling fluids). Uses: Red colour in fireworks and flares; For ceramic ferrite magnets; Added to aluminium-silicon alloys to improve their mechanical properties. Did you know? Strontium is named after the village of Strontian in Scotland. - Barium (Ba), Atomic number 56, Main group II, Period 6, metal. Electrons per shell: 2, 8, 18, 18, 8, 2. Common compounds: BaSO₄ (Barium sulfate: barely soluble and non-toxic, used as an X-ray contrast agent and in paint); BaCl₂ (Barium chloride: a starting material for other barium compounds, detects sulfate); Ba(NO₃)₂ (Barium nitrate: gives fireworks a green colour). Uses: Binds leftover gases in vacuum tubes, for example in old TV sets; Alloyed with nickel in spark plugs; Makes lead alloys for bearings harder. Did you know? In 1602, stones in Italy that glowed in the dark after heating caught attention. They contained barium. - Radium (Ra), Atomic number 88, Main group II, Period 7, metal. Electrons per shell: 2, 8, 18, 32, 18, 8, 2. Common compounds: RaCl₂ (Radium chloride: the basis of a drug for bone metastases); RaSO₄ (Radium sulfate: a barely soluble salt, like barium sulfate). Uses: Once used in capsules for cancer treatment from inside (brachytherapy); In physics classes, samples show alpha radiation in cloud chambers; Mixed with beryllium, a source of neutrons. Did you know? Until 1931, radium water called Radithor was sold as a drink. III · Boron group: Boron is a metalloid, the other elements (aluminium, gallium, indium, thallium) are metals. - Boron (B), Atomic number 5, Main group III, Period 2, borderline case (metalloid). Electrons per shell: 2, 3. Common compounds: Na₂B₄O₇ (Borax: the most important boron compound, used for insulation and bleaches); H₃BO₃ (Boric acid: used as a flux for soldering); B₄C (Boron carbide: a very hard abrasive for working steel). Uses: Fibres for tennis rackets, fishing rods and helicopter rotors, being strong and stiff; Fireworks, since it burns with an intense green flame; Igniters for airbags, as a boron-nitrate mixture. Did you know? Boron compounds were already used to make glass in ancient Rome. - Aluminium (Al), Atomic number 13, Main group III, Period 3, metal. Electrons per shell: 2, 8, 3. Common compounds: Al₂O₃ (Aluminium oxide: found as corundum, ruby and sapphire; used as an abrasive); Al(OH)₃ (Aluminium hydroxide: makes plastics and coatings more fire resistant); KAl(SO₄)₂ (Alum: used in styptic pencils for small shaving cuts). Uses: Lightweight construction in aircraft, cars and trains; Boats and ships: aluminium withstands salt water well; Light electric cables, such as overhead lines and aircraft wiring. Did you know? Aluminium used to cost more than gold. Better production methods made it cheap. - Gallium (Ga), Atomic number 31, Main group III, Period 4, metal. Electrons per shell: 2, 8, 18, 3. Common compounds: GaAs (Gallium arsenide: a semiconductor for solar cells and LEDs); GaN (Gallium nitride: a semiconductor used to make LEDs). Uses: Liquid part of thermometers (in the alloy galinstan); Coating for mirrors; Added to silicon in electronics (doping). Did you know? Gallium melts at only about 30 °C but does not boil until 2400 °C. - Indium (In), Atomic number 49, Main group III, Period 5, metal. Electrons per shell: 2, 8, 18, 18, 3. Common compounds: InAs (Indium arsenide: a semiconductor for LEDs, photodiodes and lasers); CuInSe₂ (Copper indium diselenide: the light-absorbing layer in thin-film solar cells); In₂S₃ (Indium(III) sulfide: replaces cadmium sulfide in solar cells). Uses: Most of it goes into displays, as indium tin oxide; Low-melting alloys for sprinklers and fuses; Seals in cryogenic equipment, because it stays easy to shape even when very cold. Did you know? Galinstan, an alloy containing indium, is liquid at room temperature and can replace mercury. - Thallium (Tl), Atomic number 81, Main group III, Period 6, metal. Electrons per shell: 2, 8, 18, 32, 18, 3. Common compounds: Tl₂SO₄ (Thallium sulfate: once sold as rat poison, very toxic); TlNO₃ (Thallium nitrate: gave green light in distress flares, but toxic); Tl₂S (Thallium sulfide: a material for photocells). Uses: Alloyed with lead: rollers for galvanising steel sheet; Mixed with mercury: thermometers for very low temperatures; Additive in lead tellurides for thermoelectric materials. Did you know? Thallium was spotted in 1861 by a bright green line in its light, and named after a green twig. IV · Carbon–silicon group: It reaches from carbon, a non-metal, to lead, a metal. The group is named after its first two elements. - Carbon (C), Atomic number 6, Main group IV, Period 2, non-metal. Electrons per shell: 2, 4. Common compounds: CO₂ (Carbon dioxide: a greenhouse gas that plants need for photosynthesis); CaCO₃ (Calcium carbonate: limestone, chalk, marble and seashells); Na₂CO₃ (Soda (sodium carbonate): an important raw material for glass). Uses: Graphite is the material in pencil leads; Diamond is used as an abrasive because it is so hard; Activated carbon filters dissolved substances out of liquids. Did you know? Diamond and graphite are made of the same thing: pure carbon. - Silicon (Si), Atomic number 14, Main group IV, Period 3, borderline case (metalloid). Electrons per shell: 2, 8, 4. Common compounds: SiO₂ (Silicon dioxide: the main part of sand; quartz is pure SiO2); SiO (Silicon monoxide: used to coat and improve optical lenses). Uses: Computer chips and sensors are built from silicon; An important part of most solar cells; Added to steel and cast alloys. Did you know? Horsetail and bamboo store silicon dioxide, which makes them sturdier. - Germanium (Ge), Atomic number 32, Main group IV, Period 4, borderline case (metalloid). Electrons per shell: 2, 8, 18, 4. Common compounds: GeO₂ (Germanium dioxide: a catalyst for the polyester in PET bottles); GeCl₄ (Germanium tetrachloride: helps in making optical-fibre cables); GeH₄ (Germane: a gas used in the semiconductor industry). Uses: The first diodes and transistors, until silicon replaced it; Lenses for night-vision devices and thermal cameras; Radiation detector made of a very pure crystal. Did you know? Mendeleev predicted this element in 1871, years before its discovery, and called it eka-silicon. - Tin (Sn), Atomic number 50, Main group IV, Period 5, metal. Electrons per shell: 2, 8, 18, 18, 4. Common compounds: SnO₂ (Tin dioxide (cassiterite): the main tin ore, also a mild polishing agent); Cu₂FeSnS₄ (Stannite: a rare tin ore made of copper, iron, tin and sulfur). Uses: Alloyed with copper it makes bronze; Solder: joins electronic parts on circuit boards; Tinplate: tin-coated iron sheet used for food cans. Did you know? If you bend pure tin it creaks audibly, a sound called “tin cry”. - Lead (Pb), Atomic number 82, Main group IV, Period 6, metal. Electrons per shell: 2, 8, 18, 32, 18, 4. Common compounds: PbS (Lead sulfide (galena): the most important lead ore); Pb₃O₄ (Red lead: a red powder, once used as rust-proof paint and in lead crystal); PbO₂ (Lead(IV) oxide: an electrode in car batteries). Uses: Main material of car batteries: about 60% of lead goes there; Shielding against X-rays, for example in lead aprons; Heavy weights for scuba diving. Did you know? About seven tonnes of lead went into building the Roman gate Porta Nigra. V · Nitrogen–phosphorus group: Nitrogen and phosphorus are non-metals, arsenic and antimony are metalloids, bismuth is a metal. - Nitrogen (N), Atomic number 7, Main group V, Period 2, non-metal. Electrons per shell: 2, 5. Common compounds: NH₃ (Ammonia: a sharp-smelling gas used to make fertiliser); HNO₃ (Nitric acid: used to make fertilisers and dyes); N₂O (Laughing gas: used as an anaesthetic). Uses: Liquid nitrogen is used for very strong cooling, e.g. of samples; Shielding gas for welding; Fills aircraft tyres so they cannot catch fire. Did you know? Nitrogen makes up 78 % of air, yet you cannot live on pure nitrogen. - Phosphorus (P), Atomic number 15, Main group V, Period 3, non-metal. Electrons per shell: 2, 8, 5. Common compounds: Ca₅(PO₄)₃OH (Hydroxyapatite: a phosphate that builds bones and teeth); P₄O₁₀ (Phosphorus pentoxide: a powerful drying agent and the start for phosphoric acid); P₄S₃ (Tetraphosphorus trisulfide: still used in some matchstick heads). Uses: Fertilisers: phosphates are the plant food made from phosphorus raw material; Red phosphorus is used in making matches; Red phosphorus makes some plastics harder to set on fire. Did you know? Phosphorus was first made in 1669 from boiled-down urine, and it glowed in the dark. - Arsenic (As), Atomic number 33, Main group V, Period 4, borderline case (metalloid). Electrons per shell: 2, 8, 18, 5. Common compounds: GaAs (Gallium arsenide: a semiconductor used in chips, LEDs and laser diodes); As₂O₃ (Arsenic trioxide: very poisonous, used as a pest killer in some countries); As₂S₃ (Orpiment: a yellow mineral that was once used as a paint pigment). Uses: Added to lead to make it stronger and easier to cast, for example in battery plates; Once an important ingredient of copper alloys that made them easier to work; Very pure arsenic is needed for semiconductors in electronics. Did you know? Large amounts of arsenic were found in the hair of Ötzi the Iceman, probably because he worked with copper. - Antimony (Sb), Atomic number 51, Main group V, Period 5, borderline case (metalloid). Electrons per shell: 2, 8, 18, 18, 5. Common compounds: Sb₂S₃ (Antimony trisulfide (stibnite): the main ore, once also used as black eye makeup); Sb₂O₃ (Antimony trioxide: used as a flame retardant and in making PET plastic). Uses: Hardens lead and tin in alloys; An ingredient of the lead used in batteries; Used to dope semiconductors such as silicon. Did you know? Antimony expands as it cools, so cast alloys with it fill even the finest corners. - Bismuth (Bi), Atomic number 83, Main group V, Period 6, borderline case (metalloid). Electrons per shell: 2, 8, 18, 32, 18, 5. Common compounds: Bi₂O₃ (Bismuth oxide: an additive for optical glass and technical ceramics); BiOCl (Bismuth oxychloride: a silvery pearlescent pigment in cosmetics); BiVO₄ (Bismuth vanadate: a weatherproof yellow pigment for paints and facade colours). Uses: Ingredient in alloys that melt at low temperatures; Bismuth-tin solder replaces lead solder in electronics; A less toxic replacement for lead in shotgun pellets. Did you know? In the 16th century, wooden boxes were decorated with shiny bismuth as a backdrop for colourful designs. VI · Chalcogens: The name means “ore formers”. After its first element the group is also called the oxygen group. - Oxygen (O), Atomic number 8, Main group VI, Period 2, non-metal. Electrons per shell: 2, 6. Common compounds: H₂O (Water: without it there would be no life on Earth); H₂O₂ (Hydrogen peroxide: works as a bleach); SiO₂ (Silicon dioxide: found in rocks as quartz). Uses: In steelmaking, oxygen removes unwanted impurities; Liquid oxygen lets rocket fuel burn; Extra oxygen for patients in emergency medicine. Did you know? Oxygen is the most abundant element on Earth, not only in air but also in rocks. - Sulfur (S), Atomic number 16, Main group VI, Period 3, non-metal. Electrons per shell: 2, 8, 6. Common compounds: H₂SO₄ (Sulfuric acid: a key industrial acid, mostly used to make fertiliser); H₂S (Hydrogen sulfide: a poisonous gas that smells of rotten eggs); SO₂ (Sulfur dioxide: preserves wine and dried fruit). Uses: Raw material for sulfuric acid (about 90 % of all sulfur); Makes rubber tougher (vulcanisation of rubber); An ingredient of black powder and fireworks. Did you know? As early as about 5000 BC, people in China and Egypt bleached cloth with sulfur. - Selenium (Se), Atomic number 34, Main group VI, Period 4, borderline case (metalloid). Electrons per shell: 2, 8, 18, 6. Common compounds: SeS₂ (Selenium disulfide: an ingredient in anti-dandruff shampoos); CdSe (Cadmium selenide: gives paints and pigments a strong red colour); SeO₂ (Selenium dioxide: saves energy when manganese is produced). Uses: In glassmaking: removes the green tint from glass or colours glass red; Light-sensitive drums in photocopiers and laser printers; Added to steel and copper alloys so they are easier to machine. Did you know? Selenium is named after Selene, the Greek goddess of the moon. - Tellurium (Te), Atomic number 52, Main group VI, Period 5, borderline case (metalloid). Electrons per shell: 2, 8, 18, 18, 6. Common compounds: CdTe (Cadmium telluride: a material for thin-film solar cells); TeO₂ (Tellurium dioxide: glass for optical fibres); Sb₂Te₃ (Antimony telluride: the storage layer in rewritable CDs). Uses: An additive in the metal industry; Small amounts are used for rubber, detonators and coloured glass and ceramics; Tellurium salts give fireworks a grass-green colour. Did you know? Tellurium is about as rare as gold, but much cheaper. - Polonium (Po), Atomic number 84, Main group VI, Period 6, borderline case (metalloid). Electrons per shell: 2, 8, 18, 32, 18, 6. Common compounds: PoO₂ (Polonium dioxide: a yellow or red compound of polonium and oxygen); PoS (Polonium monosulfide: a black solid that precipitates from a polonium solution); H₂Po (Hydrogen polonide: a liquid at room temperature). Uses: Removes static charge in factories, for example when rolling paper; Heat source in batteries of the Soviet Lunokhod moon rovers; Together with beryllium as a portable neutron source. Did you know? Marie and Pierre Curie found polonium in 1898 and named it after Poland, Marie's homeland. VII · Halogens: The name means “salt formers”. The elements are coloured, very reactive non-metals and form salts with metals. - Fluorine (F), Atomic number 9, Main group VII, Period 2, non-metal. Electrons per shell: 2, 7. Common compounds: CaF₂ (Calcium fluoride: occurs in nature as the mineral fluorite); HF (Hydrogen fluoride: its solution, hydrofluoric acid, etches glass); (C₂F₄)n (PTFE (Teflon): the coating of frying pans). Uses: Used to make uranium hexafluoride for nuclear fuel; Used to make sulfur hexafluoride, an insulating gas; Treating plastic surfaces, for example car fuel tanks. Did you know? Fluorine is so reactive that it almost never occurs as a pure element in nature. - Chlorine (Cl), Atomic number 17, Main group VII, Period 3, non-metal. Electrons per shell: 2, 8, 7. Common compounds: NaCl (Sodium chloride: our table salt, also found underground as rock salt); HCl (Hydrogen chloride: dissolves in water to form hydrochloric acid); KCl (Potassium chloride: mainly used as a fertiliser). Uses: Starting material for the plastic PVC (via vinyl chloride); Disinfects swimming-pool and drinking water; Bleaches paper white. Did you know? Chlorine was used in making 85 % of all medicines (as of 1995). - Bromine (Br), Atomic number 35, Main group VII, Period 4, non-metal. Electrons per shell: 2, 8, 18, 7. Common compounds: AgBr (Silver bromide: the light-sensitive substance used in photographic film); CH₃Br (Methyl bromide: a gas once used to fumigate containers against pests). Uses: Flame retardants in plastics and circuit boards; A disinfectant that is milder than chlorine; Bromine-containing rubber for airtight tyres. Did you know? Bromine and mercury are the only elements that are liquid under standard conditions. - Iodine (I), Atomic number 53, Main group VII, Period 5, non-metal. Electrons per shell: 2, 8, 18, 18, 7. Common compounds: KI (Potassium iodide: a well-known iodide in which iodine dissolves well); CaI₂ (Calcium iodide: added to foods as a source of iodine); AgI (Silver iodide: a silver salt that darkens in light). Uses: Iodised salt: table salt with added iodine, because the body needs iodine; Tincture of iodine works as an antiseptic for wounds; Sometimes used to disinfect swimming pool water. Did you know? Iodine was found by accident: cleaning pots released a violet cloud. - Astatine (At), Atomic number 85, Main group VII, Period 6, borderline case (metalloid). Electrons per shell: 2, 8, 18, 32, 18, 7. Common compounds: HAt (Hydrogen astatide: a compound of astatine and hydrogen, detected only in traces). Uses: Organic astatine compounds are used in nuclear medicine to irradiate tumours; Astatine isotopes can label the thyroid gland for examinations. Astatine is so rare and short-lived that only one compound is listed. Did you know? There are only about 100 to 130 milligrams of astatine on all of Earth. VIII · Noble gases: They react only under extreme conditions, consist of single atoms and are gases at room temperature. Helium is the most common noble gas, on Earth it is argon. - Helium (He), Atomic number 2, Main group VIII, Period 1, non-metal. Electrons per shell: 2. Uses: Fills balloons and airships, and it does not burn; Coolant for the magnets in MRI scanners; Part of breathing gas mixtures for professional diving. Helium is a noble gas and forms no known stable compounds, so none are listed. Did you know? Helium was first spotted on the Sun, hence its name (Greek helios = sun). - Neon (Ne), Atomic number 10, Main group VIII, Period 2, non-metal. Electrons per shell: 2, 8. Uses: Fills glowing tubes, which shine orange-red; Mixed with helium in helium-neon lasers; Liquid neon can serve as a coolant. No compounds of neon are known so far, so none are listed. Did you know? Calculations show neon is the element least willing to react. - Argon (Ar), Atomic number 18, Main group VIII, Period 3, non-metal. Electrons per shell: 2, 8, 8. Common compounds: HArF (Argon fluorohydride: a compound made only in the lab at extremely low temperatures). Uses: Shielding gas for welding, so the metal does not react; Filling gas in light bulbs and double-glazed windows; Fire-extinguishing gas for server rooms: it pushes out oxygen. Argon is a noble gas and forms hardly any compounds; only one is known. Did you know? After nitrogen and oxygen, argon is the third most common gas in the air. - Krypton (Kr), Atomic number 36, Main group VIII, Period 4, non-metal. Electrons per shell: 2, 8, 18, 8. Common compounds: KrF₂ (Krypton difluoride: one of the strongest known oxidising agents). Uses: Filling gas in light bulbs, so the filament can run hotter and shine brighter; Filling gas for very well insulating double-glazed windows; Used with fluorine in a UV laser (excimer laser). Only very few krypton compounds are known, so only one is listed. Did you know? From 1960 until 1983 the metre was defined using light from a krypton atom. - Xenon (Xe), Atomic number 54, Main group VIII, Period 5, non-metal. Electrons per shell: 2, 8, 18, 18, 8. Common compounds: XeF₂ (Xenon difluoride: the most stable xenon compound, used in labs to add fluorine); XeF₄ (Xenon tetrafluoride: one of three known compounds of xenon and fluorine). Uses: Fill gas in discharge lamps, including car headlights (xenon lights); Propellant in ion thrusters of satellites and space probes; Fill gas in highly insulating multi-pane windows. Did you know? Xenon is the rarest stable element on Earth. - Radon (Rn), Atomic number 86, Main group VIII, Period 6, non-metal. Electrons per shell: 2, 8, 18, 32, 18, 8. Common compounds: RnF₂ (Radon difluoride: forms when radon reacts with fluorine). Uses: Radon measurements show whether groundwater flows into a body of water; Radon measurements help in the search for uranium ore; In some countries, earthquake forecasting also relies on radon measurements. Radon is radioactive, so only one compound is listed. Did you know? Radon is by far the densest elemental gas, apart from astatine and hot iodine vapour.

Rule

For the main groups the number equals the number of electrons in the outermost shell, the outer electrons. Helium is the exception: it has only 2. Groups 13 to 18 are the main groups III to VIII (group minus 10).

Example

Example: Chlorine

Chlorine is in group 17, so in main group VII. Its electrons sit on shells 2, 8 and 7: on the outside there are 7, exactly the number of the main group.

Practice

A whole main group: Tap all elements of the group.

By outer electrons: Find an element with this many outer electrons.

By period and main group: Find the element at this place on the map.

Exercise hauptgruppe-finden

No. | group | groupName | Solution
1 | I | alkali metals and hydrogen | Hydrogen (H), Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs), Francium (Fr)
2 | VIII | Noble gases | Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn)
3 | VII | Halogens | Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At)
4 | VI | Chalcogens | Oxygen (O), Sulfur (S), Selenium (Se), Tellurium (Te), Polonium (Po)
5 | V | Nitrogen–phosphorus group | Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi)
6 | IV | Carbon–silicon group | Carbon (C), Silicon (Si), Germanium (Ge), Tin (Sn), Lead (Pb)
7 | III | Boron group | Boron (B), Aluminium (Al), Gallium (Ga), Indium (In), Thallium (Tl)
8 | II | Alkaline earth metals | Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), Radium (Ra)

Exercise aussenelektronen-finden

No. | n | Solution
1 | 6 | Oxygen (O)
2 | 5 | Nitrogen (N)
3 | 4 | Carbon (C)
4 | 3 | Boron (B)
5 | 2 | Helium (He)
6 | 1 | Hydrogen (H)
7 | 8 | Neon (Ne)
8 | 7 | Fluorine (F)

Exercise platz-finden

No. | period | group | Solution | F4
1 | 3 | I | Sodium (Na) | –
2 | 3 | VIII | Argon (Ar) | –
3 | 4 | VII | Bromine (Br) | –
4 | 5 | VI | Tellurium (Te) | Bismuth (Bi)
5 | 6 | V | Bismuth (Bi) | Tellurium (Te)
6 | 1 | VIII | Helium (He) | –
7 | 2 | VII | Fluorine (F) | Radium (Ra)
8 | 3 | VI | Sulfur (S) | Thallium (Tl)
9 | 4 | V | Arsenic (As) | Tin (Sn)
10 | 5 | IV | Tin (Sn) | Arsenic (As)
11 | 6 | III | Thallium (Tl) | Sulfur (S)
12 | 7 | II | Radium (Ra) | Fluorine (F)
13 | 2 | V | Nitrogen (N) | Strontium (Sr)
14 | 3 | IV | Silicon (Si) | Gallium (Ga)
15 | 4 | III | Gallium (Ga) | Silicon (Si)
16 | 5 | II | Strontium (Sr) | Nitrogen (N)
17 | 6 | I | Caesium (Cs) | –
18 | 6 | VIII | Radon (Rn) | –
19 | 2 | III | Boron (B) | Magnesium (Mg)
20 | 3 | II | Magnesium (Mg) | Boron (B)
21 | 4 | I | Potassium (K) | –
22 | 4 | VIII | Krypton (Kr) | –
23 | 5 | VII | Iodine (I) | –
24 | 6 | VI | Polonium (Po) | –
25 | 2 | I | Lithium (Li) | –
26 | 2 | VIII | Neon (Ne) | –
27 | 3 | VII | Chlorine (Cl) | –
28 | 4 | VI | Selenium (Se) | Lead (Pb)
29 | 5 | V | Antimony (Sb) | –
30 | 6 | IV | Lead (Pb) | Selenium (Se)
31 | 1 | I | Hydrogen (H) | –
32 | 2 | VI | Oxygen (O) | Barium (Ba)
33 | 3 | V | Phosphorus (P) | Indium (In)
34 | 4 | IV | Germanium (Ge) | –
35 | 5 | III | Indium (In) | Phosphorus (P)
36 | 6 | II | Barium (Ba) | Oxygen (O)
37 | 7 | I | Francium (Fr) | –
38 | 2 | IV | Carbon (C) | Calcium (Ca)
39 | 3 | III | Aluminium (Al) | –
40 | 4 | II | Calcium (Ca) | Carbon (C)
41 | 5 | I | Rubidium (Rb) | –
42 | 5 | VIII | Xenon (Xe) | –
43 | 6 | VII | Astatine (At) | –
44 | 2 | II | Beryllium (Be) | –

Exercise hauptgruppe-brom