Bentuk Molekul (Geometri Molekul) / Kimia Kelas XI SMA Kurikulum Merdeka

Summary

This video explores the three-dimensional shapes of molecules, distinguishing molecular geometry from simple chemical bonds. It introduces two key theories: VSEPR, which predicts shapes based on repulsion between bonding and lone electron pairs, and Electron Domain Theory, which considers regions around the central atom. Through examples like H₂O and CO₂, viewers learn to calculate lone pairs, use AXE notation, and understand how electron pair repulsion influences molecular shapes. The video also covers general shapes for molecules with 2–6 electron domains, highlighting how lone pairs distort geometry and emphasizing practical methods for predicting and visualizing molecular structures.

Takeaways

• 😀 The shape of a molecule is determined by the number of electron domains around the central atom.
• 😀 Electron pairs (bonding pairs and lone pairs) repel each other and arrange themselves to minimize repulsion.
• 😀 Bonding pairs (PEI) and lone pairs (PEB) have different repulsion strengths, with lone pairs exerting greater repulsion.
• 😀 Molecules with two bonding domains and no lone pairs (AX2E0) are linear, like BeCl2.
• 😀 Molecules like H2O with two bonding pairs and two lone pairs (AX2E2) adopt a bent or V-shaped geometry.
• 😀 Electron pair repulsion causes distortion in molecular shapes when lone pairs are present.
• 😀 Molecules with six electron domains can form various shapes: AX6 (octahedral), AX5E1 (square pyramidal), AX4E2 (square planar).
• 😀 Lone pairs affect the geometry more strongly than bonding pairs, altering ideal bond angles and shapes.
• 😀 Repulsion hierarchy is PEB > PEI > Pi, meaning lone pairs repel more strongly than bonding electrons.
• 😀 Understanding AXE notation (e.g., AX2E2, AX4E2) is crucial for predicting molecular geometries accurately.
• 😀 Electron domains, whether from bonds or lone pairs, determine molecular shapes through spatial arrangement.

Q & A

What is the main difference between chemical bonds and the shape of a molecule?

Chemical bonds describe how atoms are connected in a molecule in a 2D plane, while the shape of a molecule describes the 3D arrangement of atoms in space.

What are the two main theories used to predict molecular shape?

The two main theories are the VSEPR theory (Valence Shell Electron Pair Repulsion) and the Electron Domain Theory.

How does the VSEPR theory predict molecular shape?

VSEPR theory predicts molecular shape based on the repulsion between bonding electron pairs (PEI) and lone pairs (PEB) around the central atom, arranging them to minimize repulsion.

What is considered an electron domain in the Electron Domain Theory?

An electron domain is a region occupied by an electron pair around the central atom, and a double or triple bond counts as a single domain.

How can the number of lone pairs (PEB) be calculated quickly for single-bonded molecules?

The formula is e = (valence electrons of the central atom - number of bonding electrons (PEI)) / 2. This is accurate only for single bonds.

What is the molecular shape of H2O and why?

H2O has a bent (V-shaped) molecular shape because the oxygen central atom has two bonding pairs (PEI) and two lone pairs (PEB), which repel each other and distort the shape.

What is the molecular shape of CO2 and why?

CO2 has a linear molecular shape because the carbon central atom has two double bonds to oxygen atoms, resulting in two electron domains and no lone pairs on the central atom.

How does the presence of lone pairs (PEB) affect molecular shape?

Lone pairs occupy more space than bonding pairs, causing greater repulsion and distortion of the molecular shape, as seen in molecules like H2O.

Which type of electron pair exerts the strongest repulsion according to the transcript?

Lone pairs (PEB) exert the strongest repulsion, followed by bonding pairs (PEI), and then bonded pairs shared between two atoms (Pi).

What is the general formula AXyEz used for?

The formula AXyEz is used to classify molecular shapes, where A is the central atom, Xy is the number of bonded atoms (bonding pairs), and Ez is the number of lone pairs on the central atom.

Can a molecule with only two domains have a bent shape?

Yes, if the two domains include lone pairs (PEB), the molecule can have a bent shape, like in H2O (AX2E2), whereas AX2 without lone pairs is linear.

How are multiple bonds counted in electron domain theory versus the quick PEB formula?

In electron domain theory, double or triple bonds are counted as a single electron domain, but in the quick PEB formula, the actual number of bonding electron pairs (PEI) is used.