Kimia Dasar 1 - Teori Orbital Molekul

Summary

In this video, the Molecular Orbital Theory (MOT) is explored, contrasting it with the Valence Bond Theory (VBT). The key difference lies in MOT considering all electrons in bonding, rather than just valence electrons. The video explains the formation of molecular orbitals through atomic orbital combinations, introducing bonding and antibonding orbitals. It also covers sigma and pi bonds, their energy levels, and how bond order can be calculated. The theory is applied to homonuclear molecules like H2, and its advantages, including predicting the impossibility of compounds like He2, are highlighted. A deeper understanding of chemical bonds is provided through molecular orbital theory.

Takeaways

• 😀 Molecular Orbital Theory (MOT) differs from Valence Bond Theory (VBT) by considering all electrons, not just valence electrons, in the formation of covalent bonds.
• 😀 In MOT, atomic orbitals combine to form molecular orbitals, which can be bonding or antibonding orbitals.
• 😀 A bonding molecular orbital results when atomic orbitals overlap constructively, whereas an antibonding orbital results from destructive overlap.
• 😀 Sigma bonds occur when orbitals overlap head-on, such as s-s, s-p, or p-p orbital combinations.
• 😀 Pi bonds form between parallel p orbitals, with the bond density above and below the nuclei.
• 😀 The primary difference between sigma and pi bonds is that sigma bonds have no nodes between the nuclei, while pi bonds have a node.
• 😀 Molecular orbital theory introduces new terms like bonding molecular orbitals and antibonding molecular orbitals, with antibonding orbitals marked by an asterisk.
• 😀 Bonding orbitals are lower in energy and lead to more stable configurations, while antibonding orbitals are higher in energy and contribute to instability.
• 😀 The bond order, which indicates the strength of a bond, is calculated by subtracting the number of antibonding electrons from the bonding electrons, then dividing by 2.
• 😀 For homonuclear molecules (e.g., H2), the bond order helps predict the type of bond (single, double, etc.). Molecular orbital theory also explains why certain compounds (e.g., He2) are not possible.
• 😀 The molecular orbital theory applied in Basic Chemistry is focused on homonuclear molecules, with heteronuclear molecules studied later in inorganic chemistry.

Q & A

What is the main difference between Molecular Orbital Theory (MOT) and Valence Bond Theory (VBT)?

The main difference is that in VBT, only valence electrons contribute to the formation of bonds, while in MOT, all electrons in the atoms involved contribute to bond formation.

What is a molecular orbital, and how does it form?

A molecular orbital is formed when atomic orbitals from different atoms combine. This occurs when atoms like hydrogen (H) come together, and their atomic orbitals overlap to form new orbitals called molecular orbitals.

What are the two possible types of molecular orbitals that can form when atomic orbitals combine?

The two possible types are bonding molecular orbitals, which are lower in energy and increase stability, and antibonding molecular orbitals, which are higher in energy and decrease stability.

What is the significance of the asterisk (*) symbol in molecular orbital notation?

The asterisk (*) indicates an antibonding molecular orbital, which has higher energy and is less stable compared to the bonding orbital.

What is the difference between a Sigma (σ) bond and a Pi (π) bond?

A Sigma (σ) bond occurs when orbitals overlap head-on (e.g., s-s, s-p, or p-p), whereas a Pi (π) bond occurs when p-orbitals overlap side-by-side, passing through the node, and is typically weaker than a sigma bond.

What does it mean for a bond to be 'bonding' or 'antibonding' in Molecular Orbital Theory?

A bonding orbital has lower energy and increases the stability of a molecule, while an antibonding orbital has higher energy and decreases the molecule's stability.

How is bond order calculated in Molecular Orbital Theory?

Bond order is calculated using the formula: (Number of electrons in bonding orbitals - Number of electrons in antibonding orbitals) / 2.

What does a bond order of 1 mean in the context of a molecule like H₂?

A bond order of 1 means the molecule has a single bond, as seen in H₂, where the bonding orbital is fully occupied by electrons, and there are no electrons in the antibonding orbital.

Why do electrons fill the bonding molecular orbital before the antibonding orbital?

Electrons fill the bonding molecular orbital first because it is lower in energy and thus more stable. This is in line with the principle of minimizing energy in a molecule.

What is the significance of Molecular Orbital Theory in predicting the existence of certain compounds?

Molecular Orbital Theory helps predict the stability of molecules. For example, it can explain why molecules like He₂ do not exist because their bond order is negative, indicating instability.