Grade 10
  1. Matter and its properties  1.1. States of matter  1.2. Physical and chemical properties of matter  1.3. Classification of substances (elements, compounds, mixtures)  1.4. Changes in Matter (Physical and Chemical Changes)  1.5. Law of conservation of mass and law of definite proportions
  2. Atomic Structure  2.1. Historical development of the atomic model  2.2. Subatomic particles (protons, neutrons, electrons)  2.3. Atomic number, mass number and isotopes  2.4. Electronic Configuration and Energy Levels  2.5. Valency, ion formation and oxidation state
  3. Periodic table  3.1. History and Development of the Periodic Table  3.2. Modern Periodic Law and Periodic Trends  3.3. Groups and Periods in the Periodic Table  3.4. Trends in the Periodic Table  3.5. Metals, non-metals, metalloids and their properties  3.6. Noble gases and their chemical inertness
  4. Chemical bond  4.1. Formation of Chemical Bonds (Octet Rule)  4.2. Ionic Bonding and Properties of Ionic Compounds  4.3. Covalent Bond and Properties of Covalent Compounds  4.4. Metallic bond and its properties  4.5. Molecular geometry and VSEPR theory  4.6. Polarity and dipole moment of molecules  4.7. Intermolecular forces
  5. Chemical Reactions and Equations  5.1. Types of Chemical Reactions  5.2. Writing and balancing chemical equations  5.3. Law of conservation of mass in chemical reactions  5.4. Factors Affecting Chemical Reactions  5.5. Catalysts and their role in chemical reactions  5.6. Exothermic and Endothermic Reactions
  6. Stoichiometry and Chemical Calculations  6.1. Mole concept and Avogadro number  6.2. Molar Mass and Gram-Mole Conversions  6.3. Empirical and molecular formula  6.4. Stoichiometric calculations and chemical yield  6.5. Limiting and Excess Reactants
  7. Acids, Bases and Salts  7.1. Properties and Definitions of Acids and Bases (Arrhenius, Bronsted-Lowry, Lewis)  7.2. pH Scale, pOH, and Indicators  7.3. Neutralization reactions and salt formation  7.4. Strength of Acids and Bases (Strong vs. Weak Acids and Bases)  7.5. Common Acids and Bases in Daily Life  7.6. Salts, their solubility and applications
  8. Metals and Nonmetals  8.1. Physical and chemical properties of metals  8.2. Physical and Chemical Properties of Non-Metals  8.3. Reactivity Series of Metals and Displacement Reactions  8.4. Extraction of metals from ores  8.5. Corrosion, its causes and prevention  8.6. Alloys, their composition and uses
  9. Carbon and its compounds  9.1. Allotropes of Carbon  9.2. Hydrocarbons and their classification (alkanes, alkenes, alkynes)  9.3. Functional groups in organic compounds  9.4. Nomenclature of organic compounds (IUPAC system)  9.5. Isomerism in organic chemistry (structural and geometrical)  9.6. Important organic reactions (combustion, addition, substitution, polymerization)  9.7. Applications of organic compounds in industry and daily life
  10. Environmental Chemistry  10.1. Air Pollution (Sources, Effects and Control)  10.2. Water Pollution (Causes, Effects and Remedies)  10.3. Greenhouse effect and global warming  10.4. Ozone layer depletion and its effects  10.5. Green Chemistry and Its Applications  10.6. sustainable chemistry practice
  11. Thermochemistry  11.1. Heat and Energy Changes in Chemical Reactions  11.2. Exothermic and Endothermic Reactions  11.3. Enthalpy, enthalpy change, and heat of reaction  11.4. Specific heat capacity and calorimetry  11.5. Energy Changes in Combustion Reactions
  12. Electrochemistry  12.1. Electrolytes and non-electrolytes  12.2. Electrolysis and its applications (electroplating, extraction of metals)  12.3. Redox reactions (oxidation and reduction)  12.4. Galvanic cell and electrochemical series  12.5. Corrosion and electrochemical prevention methods
  13. Chemical kinetics and equilibrium  13.1. Rate of chemical reactions and its measurement  13.2. Factors affecting the reaction rate (catalyst, temperature, concentration)  13.3. Reversible and irreversible reactions  13.4. Dynamic equilibrium and equilibrium constant  13.5. Le Chatelier's principle and its applications
  14. Gases and Gas Laws  14.1. Properties of gases and kinetic molecular theory  14.2. Boyle's Law (Pressure-Volume Relation)  14.3. Charles's Law  14.4. Gay-Lussac's Law  14.5. Combined Gas Law and Ideal Gas Law  14.6. Real Gases vs Ideal Gases
  15. Nuclear Chemistry  15.1. Introduction to Radioactivity and Nuclear Reactions  15.2. Types of radioactive decay (alpha, beta, gamma)  15.3. Half-life and applications of radioactive isotopes  15.4. Nuclear fission and fusion reactions  15.5. Nuclear power generation and its environmental impact

Grade 10 → Chemical bond ↓


Molecular geometry and VSEPR theory


Molecular geometry is an essential concept in chemistry that deals with the three-dimensional shape of molecules. Understanding molecular geometry helps predict the behavior, reactivity, and physical properties of molecules. This subject is explained primarily through valence shell electron pair repulsion (VSEPR) theory, which is used to predict the geometry of individual molecules based on the repulsion between electron pairs in the valence shells of atoms within the molecule.

Understanding the basics

Molecules form when atoms join together. The number of atoms, the types of bonds, and the angles between the bonds define the shape of the molecule. Molecular shapes can vary considerably, affecting both physical and chemical properties, such as boiling and melting points, reactivity, and polarity.

Importance of molecular geometry

Understanding molecular geometry is important because:

  • It determines how molecules interact with each other.
  • This affects physical properties such as melting point and boiling point.
  • This affects the strength of the intermolecular forces.
  • It determines how a molecule will react in chemical reactions.

What is VSEPR theory?

Valence shell electron pair repulsion (VSEPR) theory is a simple model used to predict the geometry of molecules. It is based on the idea that electron pairs around a central atom will arrange themselves as far apart as possible to minimize the repulsion between these pairs.

Key concepts of VSEPR theory

Here are some key points to understand the VSEPR theory:

  • Electron pairs: Electrons are either bonding pairs, which are involved in chemical bonds, or lone pairs, which are nonbonding pairs.
  • Electron pair repulsion: Both bond and lone pairs repel each other. Lone pairs repel more than bond pairs.
  • Minimizing repulsion: Molecules adjust their shapes so that the valence electron pairs are located as far away from each other as possible, thereby minimizing repulsion.

Steps to predict molecular geometry using VSEPR

To determine the shape of a molecule using VSEPR theory, follow these steps:

  1. Draw the Lewis structure: Start by drawing the Lewis structure of the molecule to identify bonding and nonbonding pairs.
  2. Count the electron pairs: Identify the number of bond pairs and lone pairs of electrons around the central atom.
  3. Determine the molecular shape: Use the VSEPR model to determine the shape of a molecule based on the number of electron pairs.

Types of molecular geometries

Molecular geometry can be understood by examining the various shapes that arise from different combinations of bonded and non-bonded electron pairs. Below are some of the common geometric shapes involved in VSEPR theory.

Linear geometry

Molecules with a linear shape have two electron pairs on the central atom, resulting in a bond angle of 180°. A common example of this is carbon dioxide (CO2).

      O=C=O
O C O

Trigonal planar geometry

Molecules with trigonal planar geometry have three bonding electron pairs arranged at 120° to each other. An example of this is boron trifluoride (BF3).

       F
       ,
    F--B--F
F F F B

Tetrahedral geometry

Tetrahedral geometry is characterized by four bonding electron pairs, with a bond angle of approximately 109.5°. A well-known example is methane (CH4).

          H
          ,
    H--C--H
          ,
          H
H H H H C

Bent or angular geometry

Bent geometries occur when there are two bonding electron pairs and one or two lone pairs. Water (H2O) is a common example, with a bond angle of about 104.5°.

      H--O
         ,
         H
O H H

Triangular pyramid geometry

The trigonal pyramidal shape is formed when there are three bond pairs and one lone pair. Lone pair-pair and bond-pair repulsions result in a lower bond angle than the ideal tetrahedral geometry, which is typically around 107°. Ammonia (NH3) is an example.

        H
        ,
    H--N--H
H H H N

Effect of lone pairs on molecular geometry

Lone pairs occupy more space around the central atom than do bond pairs because of the electron density. This spatial demand reduces bond angles from their ideal values. For example, while a tetrahedral molecule has an ideal bond angle of 109.5°, the presence of a lone pair in ammonia reduces the bond angle to about 107°, and in water, two lone pairs reduce it to about 104.5°.

Examples of molecular geometry

Example 1: Methane (CH4)

The molecular shape of methane is tetrahedral with four equal CH bonds:

          H
          ,
        H--C--H
          ,
          H

The angle between the hydrogen atoms is about 109.5°, indicating a regular tetrahedron.

Example 2: Water (H2O)

Water has a bent shape due to the two lone pairs on the oxygen atom. The molecular geometry is non-linear:

    H--O
       ,
       H

The bond angle is about 104.5°, which is due to lone pair-bond pair repulsion.

Example 3: Ammonia (NH3)

Ammonia has a trigonal pyramidal geometry with one lone pair and three bond pairs:

        H
        ,
    H--N--H

The bond angle is about 107°, slightly less than that of methane due to the lone pair effect.

Conclusion

Molecular geometry is the cornerstone of chemistry that explains the shape of a molecule and its resulting properties. VSEPR theory provides a framework for predicting geometry by minimizing repulsions between electron pairs around a central atom. By applying the VSEPR model, chemists are empowered to understand and predict molecular interactions and physical properties important for research, industrial applications, and understanding natural phenomena.


Grade 10 → 4.5


U
username
0%
completed in Grade 10

← Prev (4.4)
Metallic bond and its properties
Next (4.6) →
Polarity and dipole moment of molecules

Comments 



Molecular geometry and VSEPR theory

https://www.chemistryelite.com/g10/4.5?ceal=en