Ligação covalente coordenada [Módulo 04 - Aula 04]

Summary

In this lesson, the focus is on covalent bonds, specifically covalent coordinate bonds. The video contrasts covalent bonds, where electrons are shared equally between atoms, with coordinate bonds, where a pair of electrons originates from one atom only. The example of ozone (O3) is used to explain electron distribution and how the covalent coordinate bond is formed. The video also touches on the formation of hydronium (H3O+) and ammonium (NH4+), illustrating how bonds are created and the role of lone pairs and shared electrons in molecule stability. Finally, the video encourages viewers to engage with exercises to reinforce their understanding.

Takeaways

• 😀 The covalent coordinate bond is characterized by one atom donating a pair of electrons to form a bond, unlike a regular covalent bond where both atoms contribute electrons.
• 😀 The correct term for this type of bond is 'covalent coordinate bond,' previously known as 'dative bond.'
• 😀 When constructing molecules, the goal is to achieve electronic stability with 8 electrons around each atom, following the octet rule.
• 😀 In the example of ozone (O₃), 18 valence electrons are distributed among three oxygen atoms to form the molecule, with a central oxygen atom sharing electrons from adjacent atoms to complete its octet.
• 😀 Covalent bonds in ozone involve both normal covalent bonds (where electrons are shared equally) and coordinate bonds (where one atom donates a pair of electrons).
• 😀 The shared pair of electrons in a coordinate bond is represented by a special arrow in the older style, but the IUPAC recommends using a regular line in modern diagrams.
• 😀 The structure of ozone involves one double bond and one coordinate bond, with a central oxygen atom contributing a pair of electrons to the other oxygen atoms.
• 😀 In a hydrogen ion (H⁺), such as in a hydronium ion (H₃O⁺), one hydrogen atom donates an electron pair, forming a covalent coordinate bond with oxygen.
• 😀 Ammonium (NH₄⁺) results from the combination of ammonia (NH₃) and an H⁺ ion, with the nitrogen atom sharing electrons from the hydrogen ion to form a coordinate bond.
• 😀 In ammonium, the positive charge is spread across all the atoms, not concentrated in any single atom. The nitrogen atom still has an octet with 8 electrons around it.
• 😀 The lesson concludes with a review of the correct identification of bonds in molecules, ensuring understanding of both normal and coordinate covalent bonds, and their role in molecular stability.

Q & A

What is the difference between a regular covalent bond and a coordinate covalent bond?

In a regular covalent bond, each atom contributes one electron to the shared pair. In a coordinate covalent bond, both electrons in the shared pair come from the same atom, typically called the donor atom.

What is the significance of the octet rule in covalent bonding?

The octet rule states that atoms tend to form bonds in such a way that they achieve 8 electrons in their valence shell, resulting in a stable electron configuration. This rule is crucial for understanding how atoms bond in molecules.

How is the coordinate covalent bond represented in modern chemical notation?

In modern notation, coordinate covalent bonds are represented using a single line or dash between the atoms involved. In some cases, an arrow may also be used to indicate the direction of electron donation.

Why is ozone (O₃) an important molecule, and how does it illustrate the concept of coordinate covalent bonds?

Ozone (O₃) protects the Earth from harmful ultraviolet rays. In its molecular structure, one of the bonds involves a coordinate covalent bond where both electrons come from the same oxygen atom, highlighting the nature of this bond.

How are valence electrons distributed when building the structure of O₃?

The valence electrons from the three oxygen atoms are distributed in pairs. The goal is to ensure that each oxygen atom achieves 8 electrons around it, with one of the bonds being a coordinate covalent bond.

What role do the 'donor' and 'acceptor' atoms play in a coordinate covalent bond?

In a coordinate covalent bond, the 'donor' atom provides both electrons for the bond, while the 'acceptor' atom receives one of the electrons to form the bond.

What is the geometry of molecules like O₃, and how does this relate to the concept of coordinate bonds?

The geometry of molecules like O₃ depends on the electron distribution, and coordinate covalent bonds can influence the shape. Understanding this helps explain why molecules like ozone have their specific molecular geometry, such as being angular.

How are coordinate covalent bonds identified in the hydronium ion (H₃O⁺)?

In the hydronium ion (H₃O⁺), the oxygen atom shares electrons with a hydrogen ion (H⁺) to form a coordinate covalent bond, where both electrons come from the oxygen atom.

What is the structure of the ammonium ion (NH₄⁺), and how does it involve coordinate covalent bonding?

The ammonium ion (NH₄⁺) is formed when ammonia (NH₃) reacts with a proton (H⁺). The nitrogen atom donates an electron pair to form a coordinate covalent bond with the proton, leading to a stable structure.

How does the presence of a hydrogen ion (H⁺) affect the bonding in molecules like hydronium and ammonium?

The presence of a hydrogen ion (H⁺) creates a coordinate covalent bond with atoms like oxygen in hydronium or nitrogen in ammonium, where the electron pair for bonding is donated by the atom already involved in bonding, making the molecule stable.