Name: electronegativity in polar covalent bonds
Uploaded: 2025-05-22T09:05:32.000Z
Duration: 2 min 24 s
Channel: JoVE

K12 Standards

Arizona Science Standards

High School

Physical Science

HS.P1

HS.P1U1.2

Polar Covalent Bonds

I non metalli hanno elevate energie di ionizzazione, rendendo difficile il trasferimento di elettroni di valenza da un atomo all'altro. Quindi, i non metalli tendono a condividere gli elettroni di valenza tra gli atomi, formando legami covalenti.
La coppia condivisa di elettroni nel legame covalente è chiamata coppia di legame. Tutti gli elettroni di valenza che non partecipano al legame sono chiamati coppia solitaria o elettroni di non legame.
Secondo la regola dell'ottetto, quando alcuni atomi hanno meno di otto elettroni nel loro guscio di valenza, reagiscono per formare composti stabili raggiungendo la configurazione del gas nobile più vicino.
Ad esempio, in una molecola di ammoniaca, l'azoto richiede tre elettroni in più per raggiungere la configurazione di gas nobile più vicina, o un ottetto, mentre l'idrogeno ha bisogno di un elettrone in più per raggiungere la configurazione di gas nobile più vicina, o un duetto. Pertanto, l'atomo di azoto forma legami singoli con tre atomi di idrogeno.
D'altra parte, le molecole di anidride carbonica e monossido di carbonio sono tenute insieme rispettivamente da doppi e tripli legami carbonio-ossigeno. La formazione dei doppi e tripli legami assicura che ciascuno degli atomi costituenti raggiunga la configurazione di gas nobile più vicina.
Quando si formano legami covalenti tra due atomi di elementi diversi, l'atomo più elettronegativo attrae più fortemente gli elettroni, formando un legame covalente polare. La capacità di un atomo di attrarre elettroni verso di sé è chiamata elettronegatività. Maggiore è la differenza di elettronegatività, più polare sarà il legame.
La scala di Pauling fornisce il valore di elettronegatività per ogni elemento in base ai calcoli dell'energia di legame. L'azoto è più elettronegativo del carbonio, che a sua volta è più elettronegativo dell'idrogeno.
Quindi, in un legame covalente tra carbonio e azoto, più l'azoto elettronegativo attrae gli elettroni condivisi verso di sé, mentre, in un legame tra carbonio e idrogeno, più il carbonio elettronegativo attrae la densità elettronica lontano dall'idrogeno meno elettronegativo.

Adattato da <a href="https://openstax.org/books/chemistry-2e/pages/7-2-covalent-bonding">Openstax, Chimica 2e, Sezione 7.2: Obbligazioni covalenti</a>

legami covalenti polari

I legami covalenti si formano tra due atomi quando entrambi hanno tendenze simili ad attrarre gli elettroni a sé stessi (cioè quando entrambi gli atomi hanno energie di ionizzazione e affinità elettroniche identiche o abbastanza simili). Gli atomi non metallici formano spesso legami covalenti con altri atomi non metallici. Ad esempio, la molecola di idrogeno H2, contiene un legame covalente tra i suoi due atomi di idrogeno. Quando due atomi di idrogeno, separati con una particolare energia potenziale, si avvicinano l'uno all'altro, i loro orbitali di valenza (1s) iniziano a sovrapporsi. I singoli elettroni su ciascun atomo di idrogeno interagiscono quindi con entrambi i nuclei atomici, occupando lo spazio attorno a entrambi gli atomi. La forte attrazione di ciascun elettrone condiviso su entrambi i nuclei stabilizza il sistema e l'energia potenziale diminuisce al ridursi della distanza di legame. Se gli atomi continuano ad avvicinarsi, le cariche positive dei due nuclei si respingono e l'energia potenziale aumenta. La lunghezza del legame è determinata dalla distanza alla quale si raggiunge l'energia potenziale più bassa. Il fatto che un legame sia non polare o covalente polare è determinato da una proprietà degli atomi di legame chiamata elettronegatività.

I valori di elettronegatività degli elementi furono proposti da uno dei chimici più famosi del XX secolo: Linus Pauling. L'elettronegatività è una misura della tendenza di un atomo ad attrarre elettroni (o densità elettronica) verso sé stesso. L'elettronegatività determina come sono distribuiti gli elettroni condivisi tra i due atomi in un legame. Quanto più un atomo attrae gli elettroni nei suoi legami, tanto maggiore è la sua elettronegatività. Questa descrive quanto strettamente un atomo attrae gli elettroni in un legame. È una quantità adimensionale che viene calcolata, non misurata. Pauling derivò i primi valori di elettronegatività confrontando le quantità di energia richiesta per rompere diversi tipi di legami. Gli elettroni in un legame covalente polare vengono spostati verso l'atomo più elettronegativo; quindi l'atomo più elettronegativo è quello con la carica negativa parziale. Maggiore è la differenza di elettronegatività, più polarizzata è la distribuzione degli elettroni e maggiori sono le cariche parziali degli atomi.

Legami covalenti polari

I legami covalenti si formano tra due atomi quando entrambi hanno tendenze simili ad attrarre elettroni a se stessi (cioè, quando entrambi gli atomi hanno identici o ...

Education

Didattica

JoVE Core

Organic Chemistry

Chimica Organica

Unit 1

Unità 1

Covalent Bonding and Structure

Legame covalente e struttura

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

electronegativity in polar covalent bonds

Polar covalent bonds form when atoms share electrons unevenly. This happens in covalent bonds between atoms that have similar, but not identical, tendencies to attract electrons. Nonmetal atoms often make these bonds with other nonmetals. Hydrogen gas, H2, is a simple example of a covalent bond between two hydrogen atoms.

A covalent bond begins when two atoms move close enough for their valence orbitals to overlap. In hydrogen, the 1s orbitals overlap and the single electrons on each atom interact with both nuclei. The shared electrons are attracted to both nuclei, which lowers the potential energy of the system. As the atoms get closer, the bond reaches its length at the point of lowest potential energy.

If the atoms move too close, the positive nuclei begin to repel each other. That repulsion raises the potential energy. The balance between attraction and repulsion sets the bond length. This balance helps explain why covalent bonds are stable at a specific distance.

Whether a covalent bond is polar or nonpolar depends on electronegativity. Electronegativity is an atom’s tendency to attract electron density toward itself. It is a calculated, dimensionless value, not a measured one. Linus Pauling proposed the first electronegativity values by comparing the energy needed to break different bonds.

In a polar covalent bond, the shared electrons shift toward the more electronegative atom. That atom carries the partial negative charge. The other atom carries the partial positive charge. When the electronegativity difference is larger, the bond becomes more polarized and the partial charges become larger.

Electronegativity in Polar Covalent Bonds

electronegativity-in-polar-covalent-bonds

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polar covalent bonds

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Learn how electronegativity affects polar covalent bonds, why electrons shift unevenly, and how partial charges form in shared bonds like H2.

Electronegativity in Polar Covalent Bonds | JoVE K12

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Electronegativity in Polar Covalent Bonds

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