Name: electronegativity and polar bonds
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 2 min 54 s
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PS.Chm.3.1

Electronegativity

Niet-metalen vormen covalente bindingen door elektronen te delen. Maar worden deze elektronen gelijk verdeeld over beide atomen, of trekt het ene atoom de elektronen meer aan dan het andere? Het Lewis-model geeft alle covalente bindingen weer als gelijkelijk gedeelde elektronen;dit is echter niet altijd het geval.Als gasvormige stikstof bijvoorbeeld in een elektrisch veld wordt geplaatst, zal het zich gelijkmatig tussen de polen oriënteren. Maar wanneer gasvormig waterstofchloride, een neutraal molecuul, in een elektrisch veld wordt geplaatst, oriënteert de waterstof zich naar de kathode en chloor naar de anode, wat aangeeft dat waterstof een gedeeltelijke positieve lading heeft en chloor een gedeeltelijke negatieve lading. Het vermogen van een atoom om elektronen naar zichzelf toe te trekken, wordt elektronegativiteit genoemd.Chloor zou dus elektronegatiever zijn dan waterstof, waarbij het de gedeelde elektronen naar zichzelf toe trekt, terwijl het de verwijdering van zijn eigen elektronen weerstaat. Dit maakt de binding echter niet ionisch. In een ionische binding worden elektronen overgedragen van metalen naar niet-metalen, terwijl in HCl de elektronen ongelijk verdeeld zijn.De elektronendichtheid is hoger op het chloor dan op het waterstofatoom en vormt een polaire covalente binding. Hoe groter het verschil in elektronegativiteit tussen twee atomen, hoe meer polair de binding zal zijn. Dus, naast niet-polaire covalente of ionische bindingen, worden polaire covalente bindingen gevonden in een grote verscheidenheid aan verbindingen.De Amerikaanse chemicus Linus Pauling bestudeerde energieën die nodig zijn om bindingen in moleculen zoals diatomisch chloor of waterstof te verbreken. Hij stelde een elektronegativiteitsschaal op op basis van thermochemische gegevens, die helpt bij het voorspellen van bindingstypen. Elektronegativiteit wordt geassocieerd met de ionisatie-energie en elektronenaffiniteit van de atomen.In het periodiek systeem nemen de elektronegativiteitswaarden toe van links naar rechts metalen zijn minder elektronegatief in vergelijking met niet-metalen, met uitzondering van overgangsmetalen. Bovendien nemen de elektronegativiteitswaarden af langs de kolom en met toenemende atomaire grootte, omdat atomen minder in staat zijn elektronen naar zichzelf aan te trekken. Fluor, het meest elektronegatieve element, heeft de willekeurig toegewezen elektronegativiteitswaarde van 3, 98.Francium, aan de andere kant, is het minst elektronegatieve element met een elektronegativiteitswaarde van 0, 7. Elektronegativiteit heeft geen eenheid;het kan niet experimenteel worden bepaald.

elektronegativiteit

Of een binding niet-polair of polair covalent is, wordt bepaald door een eigenschap van de bindende atomen die elektronegativiteit wordt genoemd.  Elektronegativiteitswaarden van de elementen werden voorgesteld door een van de beroemdste scheikundigen van de twintigste eeuw: Linus Pauling. Pauling onderzocht de energie die nodig is om bindingen in heteronucleaire moleculen zoals waterstof en fluoride te verbreken. Op basis van de waarden stelde hij voor dat de energie die nodig is om een binding te verbreken het gemiddelde zal zijn van de bindingsenergieën van H2 (436 kJ/mol) en F2 (155 kJ/mol), dat wil zeggen 296 kJ/mol. De experimenteel verkregen bindingsenergie van HF bedraagt echter 565 kJ/mol, wat veel hoger is dan de voorspelde waarde. Om dit verschil te verklaren, suggereerde Pauling dat de binding een ionisch karakter moet hebben, dat wordt bepaald door het concept van elektronegativiteit.  Elektronegativiteit is een maatstaf voor de neiging van een atoom om elektronen (of elektronendichtheid) naar zichzelf toe te trekken.  Elektronegativiteit bepaalt hoe de gedeelde elektronen worden verdeeld tussen de twee atomen in een binding. Hoe sterker een atoom de elektronen in zijn bindingen aantrekt, hoe groter zijn elektronegativiteit. Elektronen in een polaire covalente binding worden verschoven naar het meer elektronegatieve atoom; het meer elektronegatieve atoom is dus degene met de gedeeltelijke negatieve lading. Hoe groter het verschil in elektronegativiteit, hoe meer gepolariseerd de elektronenverdeling en hoe groter de deelladingen van de atomen. <h4>Elektronegativiteit en het Periodiek Systeem</h4> <ul> <li>De elektronegativiteit neemt toe van links naar rechts over een periode in het periodiek systeem en neemt af per groep. </li> <li>De door Pauling afgeleide elektronegativiteitswaarden volgen voorspelbare periodieke trends, waarbij de hogere elektronegativiteiten rechtsboven in het periodiek systeem staan.</li> <li>De niet-metalen, die rechtsboven liggen, hebben dus de neiging de hoogste elektronegativiteiten te hebben, waarbij fluor het meest elektronegatieve element van allemaal is (EN = 4,0). </li> <li>Metalen zijn doorgaans minder elektronegatieve elementen en de metalen uit groep 1 hebben de laagste elektronegativiteiten. </li> <li>Edelgassen zijn uitgesloten van de elektronegativiteitslijst omdat deze atomen gewoonlijk geen elektronen delen met andere atomen, omdat ze een volledige valentieschil hebben. (Hoewel edelgasverbindingen zoals XeO2 bestaan, kunnen ze alleen onder extreme omstandigheden worden gevormd en passen ze dus niet precies in het algemene model van elektronegativiteit.)</li> </ul> <h4>Elektronegativiteit versus Elektronenaffiniteit</h4> Zorg ervoor dat u elektronegativiteit en elektronenaffiniteit niet verwart. De elektronenaffiniteit van een element is een meetbare fysieke grootheid, namelijk de energie die vrijkomt of wordt geabsorbeerd wanneer een geïsoleerd gasfase-atoom een elektron verwerft, gemeten in kJ/mol. Elektronegativiteit beschrijft daarentegen hoe sterk een atoom elektronen in een binding aantrekt. Het is een dimensieloze grootheid die wordt berekend, niet gemeten. Pauling leidde de eerste elektronegativiteitswaarden af door de hoeveelheden energie te vergelijken die nodig zijn om verschillende soorten bindingen te verbreken. Hij koos voor een willekeurige relatieve schaal variërend van 0 tot 4. Deze tekst is aangepast van <a href="https://openstax.org/books/chemistry-2e/pages/7-2-covalent-bonding">Openstax, Chemistry 2e, Sectie: 7.2 Covalent Bonding.</a>

Elektronegativiteit

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&nbsp;

Electronegativity values of ...

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electronegativity and polar bonds

Electronegativity helps explain why some covalent bonds are nonpolar and others are polar covalent. It is a measure of how strongly an atom attracts shared electrons toward itself. That pull controls how electron density is distributed in a bond.

Linus Pauling proposed the first electronegativity values by studying bond energies in heteronuclear molecules such as hydrogen fluoride. He expected the bond energy of HF to be about the average of the bond energies of H2 and F2, or 296 kJ/mol. The experimental bond energy of HF was much higher, at 565 kJ/mol, which suggested the bond had some ionic character.

In a polar covalent bond, the shared electrons shift toward the more electronegative atom. That atom carries the partial negative charge. The larger the electronegativity difference between two atoms, the more the electrons are pulled to one side, and the larger the partial charges become.

Electronegativity follows clear periodic trends. It increases from left to right across a period and decreases down a group. As a result, the highest values are found toward the upper right of the periodic table, especially among nonmetals. Fluorine is the most electronegative element, with a value of 4.0, while group 1 metals have the lowest values. Noble gases are usually left off electronegativity lists because they already have full valence shells and usually do not share electrons. Some noble gas compounds, such as XeO2, can form only under extreme conditions.

Do not confuse electronegativity with electron affinity. Electron affinity is the measurable energy released or absorbed when an isolated gas-phase atom gains an electron. Electronegativity is different. It describes how strongly an atom attracts electrons in a bond, so it is calculated rather than measured. Pauling placed these values on an arbitrary relative scale from 0 to 4.

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Chemical bonds form when atoms or ions interact in ways that lower the potential energy of a molecule. Gilbert N. Lewis created a simple model to show bond formation using valence electrons, the electrons in the outer shell. In this model, electrons are shared or transferred to help atoms reach a stable electron configuration. The Lewis model helps describe two common bond types. An ionic bond forms when electrons move from a metal to a nonmetal. A covalent bond forms when two nonmetals share...

electronegativity

Electronegativity helps explain why some covalent bonds are nonpolar and others are polar covalent. It is a measure of how strongly an atom attracts shared electrons toward itself. That pull controls how electron density is distributed in a bond. Linus Pauling proposed the first electronegativity values by studying bond energies in heteronuclear molecules such as hydrogen fluoride. He expected the bond energy of HF to be about the average of the bond energies of H2 and F2, or 296 kJ/mol. The...

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Learn how electronegativity explains polar covalent bonds, Pauling’s bond-energy idea, periodic trends, and the difference from electron affinity.

Electronegativity and Polar Bonds | JoVE K12

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Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

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Electronegativity and Polar Bonds

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