Lesson 1: Intermolecular Forces PDF

# How can you compare the properties of solids and liquids? Through Kinetic Molecular Theory (Model) - **Solid- Ice** - **Liquid- Water** # The physical states of water * **Ice** * **Water** * **Steam** # The word kinetic comes from the Greek word “kinein”, which means “to move”. The kinetic...

# How can you compare the properties of solids and liquids? Through Kinetic Molecular Theory (Model) - **Solid- Ice** - **Liquid- Water** # The physical states of water * **Ice** * **Water** * **Steam** # The word kinetic comes from the Greek word “kinein”, which means “to move”. The kinetic molecular theory is based upon the assumption that atoms are in constant random motion. | State of Matter | Molecular Properties | Description| |---|---|---| | **Solid** | Molecules of solids and liquids have less internal energy and less ability to move across a large distance | The positions of solid molecules are fixed and have little freedom to move | | **Liquid** | The distance between liquid molecules is close, but their positions are not fixed, making them able to slide past each other | | | **Gas** | | | # How do molecules move around? | Phase of Matter | Permitted Movement | |---|---| | **Solid** | Vibrational, Rotational | | **Liquid** | Vibrational, Rotational, Translational | | **Gas** | Vibrational, Rotational, Translational | # Kinetic Theory | Macroscopic Properties | Microscopic Properties | |---|---| | **Solid** | Low KE levels, Retains its own shape, Highly incompressible | Slow-moving molecules, Very strong molecular bonds, Small intermolecular spacing | | **Liquid** | Higher KE levels, Takes shape of its container, Slightly compressible | Faster moving molecules, Weak intermolecular bonds, Larger intermolecular spacing | | **Gas** | High KE levels, Takes shape of its container, Highly compressible | Very fast-moving molecules, No intermolecular bonds, Very large intermolecular spacing | # What is intermolecular force? How is intermolecular force defined by the nature of particles? Intermolecular forces, often abbreviated to IMF, are the attractive and repulsive forces that arise between the molecules of a substance. These forces mediate the interactions between individual molecules of a substance. # Intermolecular forces vs. Intramolecular forces * **Intramolecular force:** Inside the molecule (chemical bond) * **Intermolecular force:** Between 2 molecules (attractive force) Intermolecular forces are responsible for most of the physical and chemical properties of matter. # The intermolecular forces of attraction in a pure substance are collectively known as van der Waals forces. # Types of Intermolecular Forces ## **1. Dipole-Dipole Forces** Dipole-dipole are attractive forces among polar molecules ### Attraction * **HCI Intermolecular Forces** +8 8- +8 8- **H─CI** ** H─CI** 8+ 8- 8+ 8- **attraction** ## **2. Hydrogen bonds** A type of dipole-dipole force that occurs when a hydrogen atom is attached to a highly electronegative atom (Oxygen, Fluorine, Nitrogen). ### Hydrogen Bond Examples 1. **Water** 2. **Water and ammonia** 3. **Hydrogen fluoride** 4. **Methanol** ## **3. Ion-Dipole Forces** These forces are similar to dipole-dipole forces except for the fact that they arise between ions and polar molecules. ### Ion-dipole Forces Examples * **Sodium Chloride (NaCl) Dissolved in Water (H₂O)** ## **4. Ion Induced Dipole Forces** In this type, a non-polar molecule is polarized by an ion placed near it. The non-polar molecules, upon obtaining a charge, behave as induced dipoles. ### Ion-induced Dipole ** Fe2+ 0 0 ** 8+ 8- **Ion-induced dipole force ** ## **5. Dipole Induced Dipole Forces** These forces are similar to ion-induced dipole forces. However, the differentiating factor is that non-polar molecules are transformed into induced dipoles due to the presence of a polar molecule nearby. ### Dipole-induced Dipole Forces **H CI** +8 -8 **Hydrogen chloride** **(polar)** **Ar** +8 -8 **Argon** **(induced dipole)** **H₂O Xenon** **Water** **(polar)** **Oxygen** **(induced dipole)** ## **6. Dispersion Forces or London Forces** - It operates for a short distance and it is the weakest force. - This kind of force arises due to the movement of electrons thus creating temporary positive and negative charged regions. ### London Dispersion Forces (London Forces) * **Step 1:** Symmetrical distribution of electrons * **Step 2:** Instantaneous dipole moment due to asymmetry, Induced dipole moment in a second atom # Intermolecular forces play an essential role in our daily lives. What concrete example/ s can you provide on how they affect our daily lives? * **Boiling and Freezing Points** * **Solubility** * **Adhesion and Cohesion** * **Phase Change** * **Surface Tension** # Force & Intermolecular Forces & their properties | Force | Model | Basis of Attraction | Energy (kJ/mol) | Example | |---|---|---|---|---| | Nonbonding (Intermolecular) | | | | | | Ion-dipole | | Ion charge- dipole charge | 40-600 | Na+..H-O-H | | H bond | | Polar bond to H- dipole charge (high EN of N, O, F)| 10-40 | Ö-H-O-H | | Dipole-dipole | | Dipole charges | 5-25 | I-CI-I | | Ion-induced dipole | | Ion charge- polarizable e cloud | 3-15 | Fe2+....O2 | | Dipole-induced dipole | | Dipole charge- polarizable e cloud | 2-10 | H-Cl-Cl-Cl | | Dispersion (London) | | Polarizable e clouds | 0.05-40 | F-F-F-F |