Name: halogens: trends and reactions
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Halogens

Les halogènes sont un groupe de cinq éléments non métalliques fluor, chlore, brome, iode et astatine-appartenant au groupe 17. Les halogènes élémentaires existent sous forme de molécules diatomiques. À température ambiante, le fluor et le chlore sont des gaz, le brome est un liquide et l'iode est un solide.On en sait moins sur les propriétés du cinquième élément, l'astate, qui est un solide rare et hautement radioactif. Les propriétés physiques des halogènes, telles que la couleur élémentaire, varient en descendant le groupe. Les rayons atomiques augmentent avec l'augmentation du nombre atomique, et le point de fusion et le point d'ébullition montrent une tendance à la hausse du fluor à l'iode.En revanche, les propriétés périodiques telles que l'électronégativité, la réactivité et l'affinité électronique diminuent dans le groupe. Les configurations électroniques des halogènes indiquent qu'ils ont sept électrons de valence et qu'il leur manque un électron pour atteindre leurs configurations de gaz noble les plus proches. Par conséquent, les halogènes présentent des électronégativités élevées avec une forte tendance à gagner un électron supplémentaire pour compléter leur octet, ce qui en fait des agents oxydants hautement réactifs et puissants par rapport aux autres groupes.Le fluor est l'agent oxydant le plus puissant parmi les halogènes et l'iode le moins. Les halogènes présentent également des affinités électron fortement négatives, qui est le changement d'énergie lorsqu'un électron est gagné par un atome neutre. Elle est exprimée en kilojoules par mole, et la valeur négative indique la nature exothermique de la réaction.Les halogènes réagissent avec la plupart des métaux pour produire des halogénures métalliques. Par exemple, le chlore et le sodium réagissent pour produire du chlorure de sodium, qui est un composé ionique. Les halogènes réagissent avec l'hydrogène pour former des composés covalents polaires appelés halogénures d'hydrogène, qui se dissolvent souvent dans l'eau pour former des acides hydrohaliques.Les halogènes réagissent également avec l'eau. La réaction du fluor avec l'eau est très exothermique, produisant du fluorure d'hydrogène un acide fort et de l'oxygène. Cependant, le chlore réagit plus lentement, produisant de l'acide chlorhydrique et de l'acide hypochloreux un puissant oxydant.De plus, les halogènes peuvent réagir les uns avec les autres, produisant des composés covalents binaires appelés composés interhalogènes. Par exemple, le brome réagit avec le fluor en formant du trifluorure de brome.

halogènes

àLes éléments du groupe 17, connus sous le nom d'halogènes, sont des non-métaux. À température ambiante, le fluor et le chlore sont des gaz, le brome est un liquide et l'iode un solide. L'astate est un élément radioactif très instable, de sorte qu'actuellement, la plupart de ses propriétés sont inconnues en raison de sa courte demi-vie. Le tennesse est un élément synthétique qui devrait également faire partie de ce groupe.  
 
 Les halogènes ne se trouvent pas sous la forme d'atomes simples mais existent en tant que molécules diatomiques. Le rayon atomique augmente du fluor à l'iode. La configuration électronique de la couche de valence des halogènes est ns2np5, et ils ont tendance à accepter un électron pour atteindre la configuration d'un gaz noble.  Les différentes propriétés des halogènes sont indiquées dans le tableau 1. 
 
 Tableau 1 : propriétés des halogènes. 
 
 <table style="margin-left: auto; margin-right: auto;">
 <tbody style="border: 1px solid black;">
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">Élément </td>
 <td style="color: black; border: 1px solid black; text-align: center;">Configuration électronique </td>
 <td style="color: black; border: 1px solid black; text-align: center;">Rayon atomique (pm) </td>
 <td style="color: black; border: 1px solid black; text-align: center;">Ei1 (kJ/mol) </td>
 <td style="color: black; border: 1px solid black; text-align: center;">Ae (kJ/mol) </td>
 <td style="color: black; border: 1px solid black; text-align: center;">Densité à 25 °C. </td>
 <td style="color: black; border: 1px solid black; text-align: center;">Point de fusion (°C) </td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">F </td>
 <td style="color: black; border: 1px solid black; text-align: center;">[He] 2s22p5</td>
 <td style="color: black; border: 1px solid black; text-align: center;">71 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">1680 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">-328 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">1,70 g/l </td>
 <td style="color: black; border: 1px solid black; text-align: center;">-219 </td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">Cl </td>
 <td style="color: black; border: 1px solid black; text-align: center;">[Ne] 3s23p5</td>
 <td style="color: black; border: 1px solid black; text-align: center;">99 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">1250 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">-348 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">3,12 g/l </td>
 <td style="color: black; border: 1px solid black; text-align: center;">-101 </td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">Br </td>
 <td style="color: black; border: 1px solid black; text-align: center;">[Ar] 4s24p5</td>
 <td style="color: black; border: 1px solid black; text-align: center;">114 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">1140 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">-324 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">3,19 g/cm3 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">-7 </td>
 </tr>
 <tr>
 <td style="color: black; border: 1px solid black; text-align: center;">I </td>
 <td style="color: black; border: 1px solid black; text-align: center;">[Kr] 5s25p5</td>
 <td style="color: black; border: 1px solid black; text-align: center;">133 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">1010 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">-295 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">3,96 g/cm3 </td>
 <td style="color: black; border: 1px solid black; text-align: center;">114 </td>
 </tr>
 </tbody>
 </table>
 
 Les affinités électroniques des halogènes ont des valeurs négatives élevées ; ainsi, les halogènes sont de puissants agents oxydants. Le fluor est l'agent oxydant le plus puissant du groupe avec l'affinité électronique la plus négative. Les halogènes réagissent avec les métaux pour gagner l'électron et produire l'halogénure de métal correspondant. Par exemple, le chlore réagit avec le fer pour donner du chlorure de fer et avec le sodium pour donner du chlorure de sodium. Les halogènes réagissent avec l'hydrogène pour former des halogénures d'hydrogène qui se dissolvent dans l'eau pour produire des acides halogénohydriques. L'acide fluorhydrique est l'haloacide le plus faible. Le fluor réagit vigoureusement avec l'eau. La réaction est hautement exothermique et produit de l'oxygène. La réaction du chlore est moins vigoureuse avec l'eau. L'acide hypochloreux produit dans cette réaction est un puissant agent oxydant. 
 
 Les halogènes réagissent les uns avec les autres pour former des composés inter-halogénés, dont beaucoup sont des composés binaires. La formule moléculaire générale pour les composés inter-halogénés est ABn, où A est l'halogène avec un numéro atomique plus élevé et c'est un nombre impair. Quelques exemples de composés inter-halogénés sont ICl, IBr, BrF, BrCl, ClF. Les halogènes réagissent avec le carbone pour former des composés importants sur le plan commercial.  Par exemple, l'éthylène réagit avec le fluor pour donner du perfluoroéthylène. 
 
 Ce texte est adapté de <a href="https://openstax.org/books/chemistry-2e/pages/6-5-periodic-variations-in-element-properties">Openstax, Chimie 2e, Section 6.5 : Variations périodiques dans les propriétés des éléments.</a>

Halogènes

Les éléments du groupe 17, connus sous le nom d’halogènes, sont des non-métaux. À température ambiante, le fluor et le chlore sont des gaz, le brome est un liquide et l’iode un solide. ...

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halogens: trends and reactions

Halogens are Group 17 nonmetals that show clear trends in structure and reactivity. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. Astatine is highly unstable and radioactive, so most of its properties are still unknown because it has a very short half-life. Tennessine is a synthetic element that is also predicted to belong to this group.

These elements do not usually exist as single atoms. Instead, they form diatomic molecules, which means each molecule has two atoms. Their atomic radius increases from fluorine to iodine, and their outer-shell electron pattern is ns2 np5. This electron arrangement helps explain why halogens tend to gain one electron and reach a noble gas configuration.

The table of halogen properties shows important changes across the group. Fluorine has the smallest atomic radius, while iodine has the largest. First ionization energy decreases from fluorine to iodine, and electron affinity stays strongly negative for the group. Because of this, halogens are powerful oxidizing agents, and fluorine is the strongest oxidizing agent in the group.

Halogens react with metals to form metal halides. For example, chlorine reacts with iron to make iron chloride, and it reacts with sodium to make sodium chloride. They also react with hydrogen to form hydrogen halides. When these dissolve in water, they produce hydrohalic acids, and hydrofluoric acid is the weakest haloacid.

Halogens also react with water, but not in the same way. Fluorine reacts very vigorously, and the reaction is highly exothermic, which means it releases a large amount of heat. It also produces oxygen. Chlorine reacts less vigorously with water, and the hypochlorous acid formed is a strong oxidizing agent.

Halogens can react with one another to form interhalogen compounds, which are often binary compounds. Their general formula is ABn, where A is the halogen with the higher atomic number and n is an odd number. Examples include ICl, IBr, BrF, BrCl, and ClF. Halogens also react with carbon to form useful compounds, such as perfluoroethylene from the reaction of ethylene with fluorine.

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halogens

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Explore halogen trends, from physical states and electron configuration to oxidizing strength, metal halides, hydrohalic acids, and interhalogen compounds.

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Halogens: Trends and Reactions

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