Periodic table - Revision history

Rongzhou: /* Element properties */

2026-09-27T15:30:37Z

Element properties

← Older revision		Revision as of 15:30, 27 September 2026
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	* '''Group 17''': Known as '''halogens''' (Greek: 'salt forming'), this group readily reacts with metals to form ionic salts, such as $NaCl$ (table salt) and $CaCl$ (used as road salt in some regions).<ref>{{#cite:Q1803}}</ref> Compounds of fluorine, the lightest halogen, is added to toothpaste and the water supply to prevent dental cavities. Polytetrafluoroethylene (PTFE), better known under the trade name teflon and widely used as anti-adhesive coating on kitchen utensils, is an [[organic compound]] of fluorine. Chlorofluorocarbon (CFC), a class of organic compounds of fluorine and chlorine, used to be the most ubiquitous aerosol propellants and refrigerants, until the Montreal convention banned their use in 1987 for depleting earth's ozone layer and contributing to the [[greenhouse effect]] of earth's atmosphere.<ref>{{#cite:Q1824}}</ref>		* '''Group 17''': Known as '''halogens''' (Greek: 'salt forming'), this group readily reacts with metals to form ionic salts, such as $NaCl$ (table salt) and $CaCl$ (used as road salt in some regions).<ref>{{#cite:Q1803}}</ref> Compounds of fluorine, the lightest halogen, is added to toothpaste and the water supply to prevent dental cavities. Polytetrafluoroethylene (PTFE), better known under the trade name teflon and widely used as anti-adhesive coating on kitchen utensils, is an [[organic compound]] of fluorine. Chlorofluorocarbon (CFC), a class of organic compounds of fluorine and chlorine, used to be the most ubiquitous aerosol propellants and refrigerants, until the Montreal convention banned their use in 1987 for depleting earth's ozone layer and contributing to the [[greenhouse effect]] of earth's atmosphere.<ref>{{#cite:Q1824}}</ref>

			[[File:Glowing-noble-gases.jpg\|thumb\|Electrified noble gases glowing]]
	* '''Group 18''': Known as '''noble gases''' and first isolated in 1895 by [[Person:William Ramsay\|William Ramsay]], <ref>{{#cite:Q1819}}</ref> this group of elements is highly unreactive and exist as odorless, colourless, and nonflammable monatomic gas under room condition.<ref>{{#cite:Q1818}}</ref> Historically, it was thought that noble gas atoms do not react with anything chemically, and can only exist in monatomic, elemental forms. However, chemists have been able to synthesise chemical compounds containing noble gases, such as $XePtF_6$, since 1962.<ref>{{#cite:Q1819}}</ref> When an electrical current is passed through, noble gases emit a colorful glow characteristic to each element. Earth's atmosphere contains trace amounts of noble gases, and to this day the principal method of isolating noble gas is via [[fractional distillation]] of liquid air.<ref>{{#cite:Q1819}}</ref>Noble gases are used as protective gas shields during welding and semi-conductor manufacturing, gas barrier in double-pane insulated windows, an inert component of breathing gas to reduce the narcotic effect of pure oxygen, and artificial color lighting.<ref>{{#cite:Q1820}}</ref>		* '''Group 18''': Known as '''noble gases''' and first isolated in 1895 by [[Person:William Ramsay\|William Ramsay]], <ref>{{#cite:Q1819}}</ref> this group of elements is highly unreactive and exist as odorless, colourless, and nonflammable monatomic gas under room condition.<ref>{{#cite:Q1818}}</ref> Historically, it was thought that noble gas atoms do not react with anything chemically, and can only exist in monatomic, elemental forms. However, chemists have been able to synthesise chemical compounds containing noble gases, such as $XePtF_6$, since 1962.<ref>{{#cite:Q1819}}</ref> When an electrical current is passed through, noble gases emit a colorful glow characteristic to each element. Earth's atmosphere contains trace amounts of noble gases, and to this day the principal method of isolating noble gas is via [[fractional distillation]] of liquid air.<ref>{{#cite:Q1819}}</ref>Noble gases are used as protective gas shields during welding and semi-conductor manufacturing, gas barrier in double-pane insulated windows, an inert component of breathing gas to reduce the narcotic effect of pure oxygen, and artificial color lighting.<ref>{{#cite:Q1820}}</ref>

	~~[[File:Glowing-noble-gases.jpg]]~~

Rongzhou: /* Notable groups */

2026-09-27T15:28:08Z

Notable groups

← Older revision		Revision as of 15:28, 27 September 2026
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	* '''Group 18''': Known as '''noble gases''' and first isolated in 1895 by [[Person:William Ramsay\|William Ramsay]], <ref>{{#cite:Q1819}}</ref> this group of elements is highly unreactive and exist as odorless, colourless, and nonflammable monatomic gas under room condition.<ref>{{#cite:Q1818}}</ref> Historically, it was thought that noble gas atoms do not react with anything chemically, and can only exist in monatomic, elemental forms. However, chemists have been able to synthesise chemical compounds containing noble gases, such as $XePtF_6$, since 1962.<ref>{{#cite:Q1819}}</ref> When an electrical current is passed through, noble gases emit a colorful glow characteristic to each element. Earth's atmosphere contains trace amounts of noble gases, and to this day the principal method of isolating noble gas is via [[fractional distillation]] of liquid air.<ref>{{#cite:Q1819}}</ref>Noble gases are used as protective gas shields during welding and semi-conductor manufacturing, gas barrier in double-pane insulated windows, an inert component of breathing gas to reduce the narcotic effect of pure oxygen, and artificial color lighting.<ref>{{#cite:Q1820}}</ref>		* '''Group 18''': Known as '''noble gases''' and first isolated in 1895 by [[Person:William Ramsay\|William Ramsay]], <ref>{{#cite:Q1819}}</ref> this group of elements is highly unreactive and exist as odorless, colourless, and nonflammable monatomic gas under room condition.<ref>{{#cite:Q1818}}</ref> Historically, it was thought that noble gas atoms do not react with anything chemically, and can only exist in monatomic, elemental forms. However, chemists have been able to synthesise chemical compounds containing noble gases, such as $XePtF_6$, since 1962.<ref>{{#cite:Q1819}}</ref> When an electrical current is passed through, noble gases emit a colorful glow characteristic to each element. Earth's atmosphere contains trace amounts of noble gases, and to this day the principal method of isolating noble gas is via [[fractional distillation]] of liquid air.<ref>{{#cite:Q1819}}</ref>Noble gases are used as protective gas shields during welding and semi-conductor manufacturing, gas barrier in double-pane insulated windows, an inert component of breathing gas to reduce the narcotic effect of pure oxygen, and artificial color lighting.<ref>{{#cite:Q1820}}</ref>

			[[File:Glowing-noble-gases.jpg]]

Rongzhou: Created page with "The periodic table is a widely-adopted way to organise different chemical elements according to their chemical properties{{#cite:Q1803}}. Below is an example of a modern periodic table: File:Periodic-table.png Elements in each column share similar chemical properties and are known as '''groups''' (or '''families'''). Each row is known as a '''period''', and contains at most one element from each group. LibreTexts Chemistry's website p..."

2026-09-27T15:24:18Z

Created page with "The periodic table is a widely-adopted way to organise different chemical elements according to their chemical properties<ref>{{#cite:Q1803}}</ref>. Below is an example of a modern periodic table: File:Periodic-table.png Elements in each column share similar chemical properties and are known as '''groups''' (or '''families'''). Each row is known as a '''period''', and contains at most one element from each group. LibreTexts Chemistry's website p..."

New page

The periodic table is a widely-adopted way to organise different chemical [[Atom#Elements|elements]] according to their chemical properties<ref>{{#cite:Q1803}}</ref>.

Below is an example of a modern periodic table:

[[File:Periodic-table.png]]

Elements in each column share similar chemical properties and are known as '''groups''' (or '''families'''). Each row is known as a '''period''', and contains at most one element from each group.

LibreTexts Chemistry's website provides online access to [https://chem.libretexts.org/Ancillary_Materials/Reference/Periodic_Table_of_the_Elements an interactive periodic table] listing various properties of the elements.

== History ==

In 1864, German chemist [[Person:Julius Lothar Meyer|Julius Lothar Meyer]] started grouping different elements by their atomic mass and chemical properties.<ref>{{#cite:Q1803}}</ref> He first presented the different groups of elements in a table towards 1870.<ref>{{#cite:Q1806}}</ref>

In 1869, [[Person:Dimitri Mendeleev|Dimitri Mendeleev]] created his version of the periodic table independently. Going one step further, he left gaps in his table and boldly predicted the existence of new, undiscovered elements based on these gaps. His version of the periodic table gained popularity in the scientific community as new elements matching his predictions were progressively discovered.<ref>{{#cite:Q1803}}</ref><ref>{{#cite:Q1806}}</ref>

[[File:Mendeleev-periodic-table.jpg]]

<blockquote>
Meyer and Mendeleev went on a long dispute over priority of their contributions.<ref>{{#cite:Q1806}}</ref>
</blockquote>

The table was progressively revised into its modern form.<ref>{{#cite:Q1806}}</ref>

== Element properties ==

=== Metals, nonmetals, and semimetals ===

All elements featured in the periodic table can be divided into three groups:<ref>{{#cite:Q1803}}</ref>

* '''Metals''': substances that are shiny, malleable (can be beaten into thin sheets), and ductile (can be stretched into thin wires) in solid, chemically pure form, excellent conductors of heat and electricity.<ref>{{#cite:Q1806}}</ref> Mostly solid under room condition (20 °C, 101 kPa).

* '''Nonmetals''': typically dull and poor conductors of electricity and heat in chemically pure form. Can be solid, liquid, or gas under room condition.

* '''Semimetals''': substances possessing some metallic properties AND some nonmetallic properties

[[File:Metal-non-metal-semi-metal.jpeg|500px]]

=== Notable groups ===

[[File:Element-groups.jpg|500px]]

* '''Group 1''': Every element in this group, except Hydrogen, is a metal. They are collectively known as ''alkali metals''. Extremely reactive, they are never found in elemental form in nature.<ref>{{#cite:Q1812}}</ref> However, some alkali metals are abundant in nature in compound form: Sodium (Na) and potassium (K) accounts for 2.8% and 2.6% of the earth's crust per mass.<ref>{{#cite:Q1811}}</ref> Compounds of Lithium, the lightest alkali metal, is used in greases, batteries, and drugs to treat bipolar disorder.<ref>{{#cite:Q1803}}</ref>

* '''Group 2''': Known as '''alkaline earth metals''', this group are similarly reactive like alkali metals, and are never found in elemental form in nature.<ref>{{#cite:Q1813}}</ref> Some lighter alkaline earth metals, like Calcium (Ca), and Magnesium (Mg), are also abundant in earth's crust, accounting for 3.6% and 2.1% of its mass respectively.<ref>{{#cite:Q1811}}</ref>

* '''Group 17''': Known as '''halogens''' (Greek: 'salt forming'), this group readily reacts with metals to form ionic salts, such as $NaCl$ (table salt) and $CaCl$ (used as road salt in some regions).<ref>{{#cite:Q1803}}</ref> Compounds of fluorine, the lightest halogen, is added to toothpaste and the water supply to prevent dental cavities. Polytetrafluoroethylene (PTFE), better known under the trade name teflon and widely used as anti-adhesive coating on kitchen utensils, is an [[organic compound]] of fluorine. Chlorofluorocarbon (CFC), a class of organic compounds of fluorine and chlorine, used to be the most ubiquitous aerosol propellants and refrigerants, until the Montreal convention banned their use in 1987 for depleting earth's ozone layer and contributing to the [[greenhouse effect]] of earth's atmosphere.<ref>{{#cite:Q1824}}</ref>

* '''Group 18''': Known as '''noble gases''' and first isolated in 1895 by [[Person:William Ramsay|William Ramsay]], <ref>{{#cite:Q1819}}</ref> this group of elements is highly unreactive and exist as odorless, colourless, and nonflammable monatomic gas under room condition.<ref>{{#cite:Q1818}}</ref> Historically, it was thought that noble gas atoms do not react with anything chemically, and can only exist in monatomic, elemental forms. However, chemists have been able to synthesise chemical compounds containing noble gases, such as $XePtF_6$, since 1962.<ref>{{#cite:Q1819}}</ref> When an electrical current is passed through, noble gases emit a colorful glow characteristic to each element. Earth's atmosphere contains trace amounts of noble gases, and to this day the principal method of isolating noble gas is via [[fractional distillation]] of liquid air.<ref>{{#cite:Q1819}}</ref>Noble gases are used as protective gas shields during welding and semi-conductor manufacturing, gas barrier in double-pane insulated windows, an inert component of breathing gas to reduce the narcotic effect of pure oxygen, and artificial color lighting.<ref>{{#cite:Q1820}}</ref>