Intermolecular Forces Of Attraction PDF

# General Types of Intermolecular Forces An **intermolecular force of attraction (IMFA)** is simply an attractive force between neighboring molecules There are three common types namely **London dispersion forces, Dipole-dipole, and Hydrogen bonds**. **London dispersion forces** are present in m...

# General Types of Intermolecular Forces An **intermolecular force of attraction (IMFA)** is simply an attractive force between neighboring molecules There are three common types namely **London dispersion forces, Dipole-dipole, and Hydrogen bonds**. **London dispersion forces** are present in molecules regardless of the polarity This is the weakest among the intermolecular forces They originate from the **fluctuations** of the electron distribution around the molecule over time Since larger molecules have larger electron clouds they exhibit stronger dispersion forces than smaller molecules On the other hand **dipole-dipole forces** are present only in **polar molecules** (i.e those with a net dipole moment) This kind of force is stronger than London dispersion forces because polar molecules have a **permanent uneven distribution** of electrons **Hydrogen bond** is a special type of dipole-dipole interaction that occurs in **molecules having a hydrogen atom bonded to an electronegative atom** such as **fluorine, oxygen, or nitrogen** It is the **strongest intermolecular force of attraction among the three**. A very good **example** of a molecule that contains only **London dispersion forces** is methane (CH4), the simplest **hydrocarbon** It is a **non-polar molecule**, and is **not capable** of any other type of intermolecular force of attraction Another **example of a hydrocarbon** is **octane (C8H18)**, a nonpolar molecule that exhibits only London dispersion forces as well Since octane is a **bigger molecule** than methane, the former is capable of **stronger dispersion forces**. An **example** of **dipole-dipole attraction** can be seen in **hydrogen chloride (HCl)** This is because the electronegativity difference between the H and the Cl atoms make the covalent bond between them **polar** Lastly hydrogen bonds can be seen in a water molecule (H2O) because **hydrogen is bonded to a highly electronegative atom which is oxygen**. **Intermolecular forces** are involved in phase changes The **IMFA in solids** are **very strong,** thus the particles are **compact** The **IMFA in liquids** are **not strong enough** to keep the particles remain in fixed positions so **liquids generally tend to resemble the shape** of their containers The **IMFA in gases** are **extremely weak or almost negligible**, thus particles are **free to move around**. ## Worksheet **Directions**: Identify the type of IMFA for the following substances and answer the questions that follow ### Substances and IMFA Types | Substance | Type of IMFA | |---|---| | 1. CO | | | 2. NH3 | | | 3. CCl4 | | **Directions**: For each of the phase changes below choose whether the intermolecular forces increased or decreased Write a checkmark (/) under the column for your answer Then answer the critical thinking questions ### Phase Changes and Increase or Decrease in IMFA | Phase Changes | Intermolecular Forces | |---|---| | Initial State | Final State | Increase | Decrease | | solid | liquid | ✓ | | | 1. liquid | solid | | ✓ | | 2. liquid | gas | | ✓ | | 3. gas | liquid | ✓ | | | 4. solid | gas | | ✓ | | 5. gas | solid | ✓ | | # Effect of Intermolecular Forces on the Properties of Substances Intermolecular forces of attraction (IMFA) control how well molecules **stick together** These affect many of the measurable physical properties of substances Read the poem below to have a preview of these properties ## IMFA, A Poem *Helen Grace L. Cabalag, 2020* Intermolecular forces vary In their effects on a substance's property The magnitude of their intensity Can be observed in a fluid's viscosity If IMFA is the topic of discussion These two properties are always in mention In liquids, there is evaporation in tubes, there is capillary action Oh before moving on to the lesson Another property caused by cohesion Striders walk without hesitation Present in water, there is surface tension The rule "like dissolves like" in solution Is the same in the forces of attraction The very core of the explanation To a table salt-water combination Whether it is high or low, it is ranging Boiling and melting points are always changing IMFA need a little bit of explaining For extreme temperatures in H-bonding The **intermolecular forces** are associated with the observable properties of various substances The **physical properties of molecules** depend upon the type and **strength of their intermolecular forces of attraction** These properties are **solubility, melting point, boiling point, surface tension, viscosity, capillary action, and evaporation rate**. When it comes to **solubility,** the solute and the solvent **mix** when they both exhibit the **same** intermolecular forces of attraction The **melting and boiling points** of substances with **stronger IMFA** are higher compared to those with weaker IMFA In the case of **surface tension,** molecules with **stronger intermolecular forces of attraction** will exert greater cohesive forces and acquire less surface area ## Surface Tension Explained Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible Surface tension is what allows objects with a higher density than water such as razor blades and insects to float on a water surface without becoming even partly submerged Wikipedia Surface Tension: "The property of the surface of a liquid that allows it to resist an external force due to the cohesive nature of its molecules". It seems to defy the laws of physics but a paper clip made of steel can indeed float on the water surface ## Viscosity Explained **Viscosity** is a measure of a **fluid's resistance to flow** A fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion (higher surface tension) than those with weaker IMFA **Viscosity** is also affected by intermolecular forces Molecules with stronger intermolecular forces of attraction have greater **resistance to flow,** and thus **higher viscosity** compared to those with weaker IMFA This is also true in **capillary action** **Capillary action** is something that you observe when you dip a paper towel in water and the water "magically climbs up the towel" The water molecules climb up the towel and drag other water molecules along the way A **better capillary action** indicates **stronger intermolecular forces** This trend however is different in **evaporation** The lower the evaporation rate the weaker the intermolecular forces ## Worksheet (Continued) **Directions**: The boiling and melting points of HCl and O2 are shown below Determine the type of intermolecular force of attraction exhibited by the molecules ### Melting & Boiling Point and IMFA Types | Molecule | Boiling Point | Melting Point | Type of IMFA | |---|---|---|---| | 1. HF | 20°C | -83 °C | Dipole-dipole (hydrogen bonding) | | 2. O2 | -182°C | -218 °C | London dispersion forces | # Nuclear Reactions **Directions**: Determine the type of chemical reaction in each item (a-emission, b-emission, y-emission, fission, fusion) In addition write the product of the following chemical reactions on the space provided for the product side 1. 1532P -> 1632S + **00-1n** (beta emission) 2. 92238U -> 90234Th + **24He** (alpha emission) 3. 90234Th -> 90234Th + **00-1n** (gamma emission) 4. 53131I -> 54131Xe + **0-1e** (beta emission) 5. 88226Ra -> 86222Rn + **24He** (alpha emission) # Stellar Evolution **Directions**: Identify the elements formed during the following stages of star formation and evolution ### Elements formed during Stellar Evolution | Stages | What were the elements formed? | How were these elements formed? | |---|---|---| | Protostar | Hydrogen | | | Main Sequence Star | Hydrogen, Helium | Hydrogen fusion to form Helium | | Red Giant Star | Helium, Carbon, Oxygen | Helium fusion to form Carbon and Oxygen | | White Dwarf | Carbon, Oxygen | | | Supernova | Heavier, heavier elements | |