Homonuclear diatomic molecules

Key point: Electrons in atomic orbitals of the same symmetry but on neighbouring atoms are paired to form and bonds.A similar description can be applied to more complex molecules, and we begin by considering homonuclear diatomic molecules, diatomic molecules in which both atoms belong to the same element (dinitrogen, N₂, is an example). To construct the VB description of N₂, we consider the valence electron configuration of each atom, which from Section 1.8 we know to be 2s²2p_z¹2p_y¹2p_x¹. It is conventional to take the z-axis to be the internuclear axis, so we can imagine each atom as having a 2pz orbital pointing towards a 2p_z orbital on the other atom, with the 2p_x and 2p_y orbitals perpendicular to the axis. A α bond is then formed by spin pairing between the two electrons in the opposing 2p_z orbitals. Its spatial wavefunction is still given by eqn 2.1, but now X_A and X_B stand for the two 2p_z orbitals. A simple way of identifying a bond is to envisage rotation of the bond around the inter nuclear axis: if the wavefunction remains unchanged, the bond is classified as Ϭ.

The remaining 2p orbitals cannot merge to give Ϭ bonds as they do not have cylindrical symmetry around the internuclear axis. Instead, the orbitals merge to form two bonds. A bond arises from the spin pairing of electrons in two p orbitals that approach side by side (Fig. 2.4). The bond is so-called because, viewed along the internuclear axis, it resembles a pair of electrons in a p orbital. More precisely, an electron in a bond has one unit of orbital angular momentum about the internuclear axis. A simple way of identifying a bond is to envisage rotation of the α bond through 180° around the internuclear axis. If the signs (as indicated by the shading) of the lobes of the orbital are interchanged, then the bond is classified as α.

There are two bonds in N₂, one formed by spin pairing in two neighbouring 2p_x orbit als and the other by spin pairing in two neighbouring 2py orbitals. The overall bonding pattern in N2 is therefore a bond plus two α bonds (Fig. 2.5), which is consistent with the structure NN. Analysis of the total electron density in a triple bond shows that it has cylindrical symmetry around the internuclear axis, with the four electrons in the two bonds forming a ring of electron density around the central bond.

Fig. 2.4 The formation of a bond.

Fig. 2.5 The VB description of N₂. Two electrons form a Ϭ bond and another two pairs form two bonds. In linear molecules, where the x- and y-axes are not specified, the electron density of α bonds is cylindrically symmetrical around the internuclear axis.

اخر الاخبار

اخبار العتبة العباسية المقدسة

أكثر من 10,000 مستفيدة من خدمات معهد القرآن الكريم النسوي في زيارة الأربعين

بالأرقام.. قسم العلاقات العامة يحصي خدماته في زيارة الأربعين

قسم المضيف يعلن تقديم أكثر من 7 ملايين وجبة طعام لزائري الأربعين

قسم الاتصالات: أكثر من 16 ألف حالة فقدان أُعيدت لذويها بجهود العتبتين المقدستين

المزيد

الآخبار الصحية

"ساعة الذئب" تؤرق الملايين.. حل علمي ينقذ نومك

يخفف الألم.. معجون أسنان مصنوع من الشعر ؟!

كوابيسك ليست عشوائية.. ماذا تحاول أن تخبرك؟

5 مخاطر غير متوقعة لتناول البروتين بكثرة

المزيد

الآخبار التكنلوجية

أندرويد 16 على الأبواب..هاتفك سيصبح وكيلك الذكي !

"غوغل" مهددة ببيع متصفحها الشهير "كروم".. من المشتري؟

"ناسا" و"غوغل" تطوران مساعدا طبيا ذكيا لمرافقة رواد الفضاء

هل تشغيل تكييف السيارة على "الحد الأقصى" ضار؟

المزيد

مواضيع ذات صلة

Polyatomic molecules

The hydrogen molecule

The basic shapes

Resonance

Polarizability

Electronegativity

Electron affinity

Atomic and ionic radii

The format of the periodic table

The periodic table

Penetration and shielding

The angular variation of atomic orbitals