Struktur Molekul Dasar - Kimia Kelas XI

SmarterIndo

27 Jul 201603:54

Summary

TLDRThe script discusses the various molecular geometries that arise from different arrangements of atoms and bonds. It covers seven key shapes: linear, trigonal planar, trigonal pyramidal, square planar, tetrahedral, trigonal bipyramidal, and octahedral. Examples include beryllium chloride, carbon dioxide, boron trifluoride, ammonia, methane, phosphorus pentachloride, and sulfur hexafluoride. The bond angles between atoms are also explained, highlighting how different spatial arrangements lead to distinct molecular shapes, such as 180° for linear and 109.5° for tetrahedral molecules.

Takeaways

🧬 A material is always made up of various types of atoms, and their arrangement is limited by bond angles and particle properties.
⚛️ There are seven basic molecular shapes: linear, trigonal planar, trigonal pyramidal, square planar, tetrahedral, trigonal bipyramidal, and octahedral.
➡️ A molecule is linear when its atoms are arranged in a straight line, with bond angles of 180° (e.g., beryllium chloride and carbon dioxide).
🔺 Trigonal planar molecules consist of four atoms where all atoms lie in the same plane, forming a triangular arrangement (e.g., boron trichloride, boron trifluoride).
🏔️ Trigonal pyramidal molecules form a pyramid shape with a central atom at the top and others at the base, with NH3 (ammonia) being an example.
🔳 Square planar molecules consist of five atoms arranged in a square, with the central atom in the middle (e.g., xenon fluoride).
⬛ Tetrahedral molecules are structured around a central atom with four others forming a pyramid-like shape, such as methane (CH4) with a bond angle of 109.5°.
🔶 Trigonal bipyramidal molecules consist of six atoms with two pyramid shapes sharing a base, featuring two different bond angles: 120° and 90° (e.g., phosphorus pentachloride, PCl5).
⏹️ Octahedral molecules consist of seven atoms with bond angles of 90°, forming an octahedral shape, such as sulfur hexafluoride (SF6).
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Q & A

What is the composition of a material according to the script?
-A material is always composed of several types of atoms. The arrangement of atoms is limited by bond angles and the properties of the constituent particles.
What are the seven molecular shapes mentioned in the script?
-The seven molecular shapes mentioned are linear, trigonal planar, trigonal pyramidal, square planar, tetrahedral, trigonal bipyramidal, and octahedral.
What defines a linear molecule, and can you provide examples?
-A molecule is considered linear when its constituent atoms are arranged in a straight line. Examples include beryllium chloride (BeCl2) and carbon dioxide (CO2), with bond angles of 180 degrees.
What are the characteristics of a trigonal planar molecule, and can you give examples?
-A trigonal planar molecule consists of four atoms with three surrounding the central atom in a triangular shape, all on the same plane. Examples include boron trichloride (BCl3) and boron trifluoride (BF3).
How does a trigonal pyramidal molecule differ from a trigonal planar molecule?
-A trigonal pyramidal molecule is not flat and consists of a central atom at the top of a pyramid with three atoms at the base, forming a three-dimensional structure. An example is ammonia (NH3).
What is a square planar molecule, and what is an example?
-A square planar molecule consists of five atoms, with four surrounding the central atom in a square shape. An example is xenon tetrafluoride (XeF4), with bond angles of 90 degrees.
What is the bond angle in a tetrahedral molecule, and can you provide an example?
-In a tetrahedral molecule, the bond angle is 109.5 degrees. An example of a tetrahedral molecule is methane (CH4).
What is the structure of a trigonal bipyramidal molecule, and can you provide an example?
-A trigonal bipyramidal molecule consists of six atoms with a central atom surrounded by atoms in two pyramids that share the same base. An example is phosphorus pentachloride (PCl5). The bond angles are 120 degrees in the plane and 90 degrees between the planes.
What defines an octahedral molecule, and what is an example?
-An octahedral molecule has a central atom surrounded by six other atoms in a geometric shape resembling two pyramids joined at their bases. An example is sulfur hexafluoride (SF6), with bond angles of 90 degrees.
What is the bond angle in a trigonal bipyramidal molecule between the axial and equatorial positions?
-In a trigonal bipyramidal molecule, the bond angle between the atoms in the triangular plane is 120 degrees, while the bond angle between the equatorial and axial positions is 90 degrees.

Outlines

00:00

🔬 Molecular Geometry and Atom Arrangements

This paragraph introduces the concept of molecular geometry and how different molecules are structured based on their atomic arrangements. It highlights that molecules are made up of a few types of atoms, whose arrangements are influenced by the bond angles and properties of the constituent particles. The text briefly introduces seven basic molecular shapes: linear, trigonal planar, trigonal pyramidal, square planar, tetrahedral, trigonal bipyramidal, and octahedral.

➖ Linear Molecular Structure

A linear molecule is characterized by all of its constituent atoms being aligned in a straight line. Examples include beryllium chloride (BeCl₂) and carbon dioxide (CO₂). In these structures, the bond angle between the atoms is 180 degrees.

🔺 Trigonal Planar Structure

Molecules with a trigonal planar shape consist of four atoms arranged in the same plane, with the central atom surrounded by three others at the corners of a triangle. This structure is seen in compounds like boron trichloride (BCl₃) and boron trifluoride (BF₃). The bond angles in these molecules are 120 degrees.

🏔️ Trigonal Pyramidal Structure

In a trigonal pyramidal molecule, the central atom is located at the top of a pyramid with the other atoms at the vertices. This shape is different from the trigonal planar structure as it is three-dimensional. A notable example is ammonia (NH₃), where the molecule is not flat but has a three-dimensional configuration.

🔳 Square Planar Structure

Square planar molecules consist of five atoms, all in the same plane, with the central atom at the center of a square and four other atoms at the corners. An example of this structure is xenon tetrafluoride (XeF₄), with bond angles of 90 degrees between the central atom and the surrounding atoms.

🟧 Tetrahedral Structure

A tetrahedral molecule has four surrounding atoms arranged at the corners of a tetrahedron, forming a three-dimensional shape. This structure features bond angles of approximately 109.5 degrees. Methane (CH₄) is a prime example of a tetrahedral molecule, where the central atom is at the center of the tetrahedron.

🔻 Trigonal Bipyramidal Structure

The trigonal bipyramidal shape consists of two pyramids that share a base, resulting in six atoms: the central atom is at the center, with other atoms positioned at the vertices of the pyramids. The bond angles within the trigonal bipyramidal shape vary: 120 degrees within the triangular plane and 90 degrees between the top/bottom atoms and the plane. An example is phosphorus pentachloride (PCl₅).

🔷 Octahedral Structure

The octahedral structure has eight faces and consists of seven atoms. The central atom is positioned in the center of a square plane, with six atoms surrounding it at 90-degree angles. This structure results in an octahedral shape with symmetrical faces. Sulfur hexafluoride (SF₆) is an example of a molecule with this structure.

Mindmap

Keywords

💡Atom

An atom is the basic unit of matter that consists of protons, neutrons, and electrons. In the context of the video, atoms are the building blocks of molecules, and their arrangement determines the molecular geometry. The script mentions that the number of atoms is limited by the bonding angles and properties of the particles, which is crucial for understanding molecular structure.

💡Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is a central theme of the video, as different molecular shapes have different properties and reactivities. The script explains various geometries such as linear, trigonal planar, tetrahedral, and octahedral, which are essential for understanding how molecules are structured.

💡Linear

A linear molecular geometry is one where the atoms are arranged in a straight line. The video uses beryllium chloride (BeCl2) and carbon dioxide (CO2) as examples of linear molecules. In these molecules, the bonding angle is 180 degrees, which is a key characteristic of linear geometry.

💡Trigonal Planar

Trigonal planar geometry is characterized by four atoms with all atoms lying in the same plane, forming a triangle around a central atom. The script mentions boron trichloride (BCl3) and boron trifluoride (BF3) as examples. This geometry is flat and the atoms are arranged symmetrically around the central atom.

💡Trigonal Pyramidal

Trigonal pyramidal geometry is a variation of trigonal planar where the central atom is located off-center, creating a three-dimensional shape with a triangular base. Ammonia (NH3) is given as an example in the script, where the nitrogen atom is at the apex, and the hydrogen atoms form the base, illustrating the non-planar nature of this geometry.

💡Tetrahedral

A tetrahedral molecular geometry consists of a central atom surrounded by four other atoms, all of which are located at the corners of a tetrahedron. Methane (CH4) is used as an example in the script, where the carbon atom is at the center and the hydrogen atoms are at the corners. The bond angles in a tetrahedral geometry are approximately 109.5 degrees.

💡Trigonal Bipyramidal

Trigonal bipyramidal geometry occurs when a molecule has six atoms, with the central atom at the center of a trigonal base and the other atoms at the vertices. The script uses phosphorus pentachloride (PCl5) as an example, where the chlorine atoms form a trigonal bipyramid around the phosphorus atom. The bond angles in this geometry are not equal, with 120 degrees in the triangular plane and 90 degrees between the central plane and the axial atoms.

💡Octahedral

An octahedral geometry is characterized by six atoms arranged around a central atom, with the atoms forming the vertices of an octahedron. The video script mentions sulfur hexafluoride (SF6) as an example, where the sulfur atom is at the center and the fluorine atoms are at the vertices. In an octahedral molecule, the bond angles are 90 degrees.

💡Bond Angle

The bond angle is the angle between any two bonds that are connected to the same atom. It is a critical factor in determining molecular geometry. The script provides specific bond angles for different geometries, such as 180 degrees in linear molecules, 109.5 degrees in tetrahedral molecules, and 90 degrees in octahedral molecules.

💡Valence Shell Electron Pair Repulsion (VSEPR) Theory

While not explicitly mentioned in the script, the VSEPR theory is fundamental to understanding molecular geometry. It states that electron pairs around a central atom will arrange themselves to minimize repulsion, leading to the observed molecular shapes. The script's descriptions of different geometries align with the predictions of VSEPR theory.

💡Hybridization

Hybridization refers to the concept where atomic orbitals mix to form new hybrid orbitals that are suitable for bonding in molecules. Although not directly mentioned in the script, the idea of hybridization is implicit in the discussion of molecular geometries, as it explains how atoms can form more than the usual number of bonds (e.g., sp3 hybridization in tetrahedral molecules).

Highlights

Atoms are limited by the angle between bonds and the properties of the particles that make them up.

There are seven basic molecular shapes: linear, trigonal planar, trigonal pyramidal, square planar, tetrahedral, trigonal bipyramidal, and octahedral.

A molecule is linear when its atoms are aligned in a straight line, such as beryllium chloride and carbon dioxide, with a bond angle of 180 degrees.

Trigonal planar molecules consist of four atoms in the same plane, with a central atom surrounded by three others, at 120-degree bond angles, examples being boron trichloride and boron trifluoride.

Trigonal pyramidal molecules have a three-sided pyramid shape, with a central atom at the apex. Unlike trigonal planar, this shape is not flat, as seen in ammonia (NH3).

Square planar molecules consist of five atoms in the same plane, with a central atom at the center of a square, like xenon tetrafluoride (XeF4), with bond angles of 90 degrees.

Tetrahedral molecules have five atoms, with the central atom at the center of a tetrahedron. Examples include methane (CH4), with bond angles of 109.5 degrees.

Trigonal bipyramidal molecules consist of six atoms, with the central atom located at the center of two pyramids. Bond angles are 120 degrees in the triangular plane and 90 degrees between the central and axial atoms, as seen in phosphorus pentachloride (PCl5).

Octahedral molecules consist of seven atoms, with the central atom at the center of an octahedron. Bond angles are 90 degrees, as found in sulfur hexafluoride (SF6).

In linear molecules, such as beryllium chloride and carbon dioxide, the bond angle between atoms is exactly 180 degrees.

Trigonal pyramidal molecules, such as ammonia (NH3), differ from trigonal planar structures by having a three-dimensional, non-flat shape.

Square planar molecules, like xenon tetrafluoride (XeF4), have a bond angle of 90 degrees between atoms in the same plane.

The tetrahedral shape, exemplified by methane (CH4), has a bond angle of 109.5 degrees, making it a highly symmetric structure.

In a trigonal bipyramidal structure, bond angles in the triangular plane are 120 degrees, while those between the central and axial atoms are 90 degrees, as in phosphorus pentachloride (PCl5).

Octahedral molecules, like sulfur hexafluoride (SF6), have a bond angle of 90 degrees between adjacent atoms, forming a highly symmetrical shape.