3 Types of Intermolecular Forces

3 Types of Intermolecular Forces Intermolecular forces or IMFs are physical forces between molecules. In contrast, intramolecular forces are forces between atoms within a single molecule. Intermolecular forces are weaker than intramolecular forces. The interaction between intermolecular  forces may be used to describe  how molecules interact with each other. The strength or weakness of intermolecular forces determines the state of matter of a substance (e.g., solid, liquid, gas) and some of the chemical properties (e.g., melting point, structure). There are three major types of intermolecular forces: London dispersion force, dipole-dipole interaction, and ion-dipole interaction. Key Takeaways: Intermolecular Forces Intermolecular forces act between molecules. In contrast, intramolecular forces act within molecules.Intermolecular forces are weaker than intramolecular forces.Examples of intermolecular forces include the London dispersion force, dipole-dipole interation, ion-dipole interaction, and van der Waals forces. Heres a closer look at these 3 intermolecular forces, with examples of each type. London Dispersion Force The London dispersion force is also known as LDF,  London forces, dispersion forces, instantaneous dipole forces, induced dipole forces, or the induced dipole-induced dipole force The London dispersion force is the weakest of the intermolecular forces.This is the force between two nonpolar molecules. The electrons of one molecule are attracted to the nucleus of the other molecule, while repelled by the other molecules electrons. A dipole is induced when the electron clouds of the molecules are distorted by the attractive and repulsive electrostatic forces. Example:  An example of London dispersion force is the interaction between two methyl (-CH3) groups. Example: Another example is the interaction between nitrogen gas (N2) and oxygen gas (O2) molecules. The electrons of the atoms are not only attracted to their own atomic nucleus, but also to the protons in the nucleus of the other atoms. Dipole-Dipole Interaction Dipole-dipole interaction occurs whenever two polar molecules get near each other. The positively charged portion of one molecule is attracted to the negatively charged portion of another molecule. Since many molecules are polar, this is a common intermolecular force. Example:  An example of dipole-dipole interaction is the interaction between two sulfur dioxide (SO2) molecules, where the sulfur atom of one molecule is attracted to the oxygen atoms of the other molecule. Example: H​ydrogen bonding is considered a specific example of a dipole-dipole interaction always involving hydrogen. A hydrogen atom of one molecule is attracted to an electronegative atom of another molecule, such as an oxygen atom in water. Ion-Dipole Interaction Ion-dipole interaction occurs when an ion encounters a polar molecule. In this case, the charge of the ion determines which part of the molecule attracts and which repels. A cation or positive ion would be attracted to the negative part of a molecule and repelled by the positive part. An anion or negative ion would be attracted to the positive part of a molecule and repelled by the negative part. Example:  An example of the ion-dipole interaction is the interaction between a Na ion and water (H2O) where the sodium ion and oxygen atom are attracted to each other, while the sodium and hydrogen are repelled by each other. Van der Waals Forces Van der Waals forces are the interaction between uncharged atoms or molecules. The forces are used to explain the universal attraction between bodies, the physical adsorption of gases, and the cohesion of condensed phases. The van der Waals forces include Keesom interaction, the Debye force, and the London dispersion force. So, van der Waals forces include intermolecular forces and also some intramolecular forces. Sources Ege, Seyhan (2003). Organic Chemistry: Structure and Reactivity. Houghton Mifflin College. ISBN 0618318097. pp. 30–33, 67.Majer, V. and Svoboda, V. (1985). Enthalpies of Vaporization of Organic Compounds. Blackwell Scientific Publications. Oxford. ISBN 0632015292.Margenau, H. and Kestner, N. (1969). Theory of Inter-molecular Forces. International Series of Monographs in Natural Philosophy. Pergamon Press, ISBN 1483119289.

Definition of Work in Physics

Definition of Work in Physics In  physics, work is defined as a  force  causing the movement- or displacement- of an object. In the case of a constant force, work is the scalar product of the force acting on an object and the displacement caused by that force. Though both force and displacement are vector quantities, work has no direction due to the nature of a scalar product (or dot product) in vector mathematics. This definition is consistent with the proper definition because a constant force integrates to merely the product of the force and distance. Read on to learn some real-life examples of work as well as how to calculate the amount of work being performed. Examples of Work There are many examples of work in everyday life.  The Physics Classroom  notes a few: a horse pulling a plow through the field; a father pushing a grocery cart down the aisle of a grocery store; a student lifting a backpack full of books upon her shoulder; a weightlifter lifting a barbell above his head; and an Olympian launching the shot-put. In general, for work to occur, a  force has to be exerted on an object causing it to move. So, a frustrated person pushing against a wall, only to exhaust himself, is not doing any work because the wall does not move. But, a book falling off a table and hitting the ground would be considered work, at least in terms of physics, because a force (gravity) acts on the book causing it to be displaced in a downward direction. Whats Not Work Interestingly, a waiter carrying a tray high above his head, supported by one arm, as he walks at a steady pace across a room, might think hes working hard. (He might even be perspiring.) But, by definition, he is not doing  any  work. True, the waiter is using force to push the tray above his head, and also true, the tray is moving across the room as the waiter walks. But, the force- the waiters lifting of the tray- does not cause the tray to move. To cause a displacement, there must be a component of force in the direction of the displacement, notes The Physics Classroom. Calculating Work The basic calculation of work is actually quite simple: W Fd Here, W stands for work, F is the force, and d represents displacement (or the distance the object travels).  Physics for Kids  gives this example problem: A baseball player throws a ball with a force of 10 Newtons. The ball travels 20 meters. What is the total work? To solve it, you first need to know that a Newton is  defined as the force necessary to provide a mass of 1  kilogram (2.2 pounds)  with an acceleration of 1  meter (1.1 yards) per second. A Newton  is generally abbreviated as N. So, use the formula: W Fd Thus: W 10 N * 20 meters (where the symbol * represents times) So: Work 200 joules A  joule,  a term used in physics, is equal to the  kinetic energy  of 1 kilogram moving  at 1 meter per second.