Polarity of molecules and its properties

• Glacial erosion involves two main forms: abrasion and plucking
• Abrasion in glacial environments is a sandpapering effect caused by small rocks embedded within the glacier rubbing on bedrock, leaving a smooth surface with scratches called striations
• Plucking occurs when meltwater from glaciers freeze around broken or cracked parts of rock, breaking it off from the bedrock or sides as the ice moves down the slope
• Freud's superego is the moral component of the psyche, representing internalized societal values and standards
• After going through the module on Polarity of Molecules, students are expected to define solubility, miscibility, and polarity; identify different types of intermolecular forces of attraction; and explain how polarity of molecules relates to their properties
• The module on Polarity of Molecules is divided into three lessons, with Lesson 1 focusing on Properties of Molecules based on their Polarity
• Activity: Word cryptogram - unscramble letters to find the correct answer for each number and complete a riddle about the three-dimensional arrangement of bonding groups of atoms around a central atom

  
• Polarity, Solubility, and Miscibility:

  • Solubility: ability of a solid substance to be dissolved in a given amount of solvent
  • Miscibility: ability of two liquids to combine or mix in all proportions, creating a homogenous mixture
  • "Like dissolves like" or "like mixes with like" - polar substances mix with polar substances, nonpolar with nonpolar
  • Exercise: determine which substances will mix based on their polarity
• Bond Strength and Physical Properties of Covalent Compounds:

  • Intermolecular forces of attraction (IMFA) exist between molecules
  • Types of IMFA from strongest to weakest: Ion-dipole, H-bonding, dipole-dipole, dipole-induced dipole, London forces of attraction
  • IMFA strength affects physical properties like boiling point, melting point, vapor pressure, and surface tension
• Table 1: Summary of Types of Intermolecular Forces of Attraction (IMFA):

  • Ion-dipole: ion and polar molecule
  • Hydrogen bonding: polar molecules with H bonded to N, O, or F
  • Dipole-dipole: between polar molecules
  • Dipole-induced dipole: between polar and nonpolar molecules
  • London forces: for nonpolar molecules and noble gases
• Table 2: General Properties of polar and nonpolar molecules:

  • Polar molecules have H-bonding and dipole-dipole IMFA, exist as solids or liquids, high boiling/melting points, high surface tension, low vapor pressure, low volatility, soluble in water
  • Nonpolar molecules have London dispersion IMFA, exist as gases, low boiling/melting points, low surface tension, high vapor pressure, high volatility, insoluble in water
• Physical Properties of Substances:

  • Boiling point: temperature at which vapor pressure and atmospheric pressure of a liquid are equal, stronger IMFA leads to higher boiling point
  • Melting point: temperature at which solid becomes liquid, melting point increases with stronger IMFA
• Methyl alcohol has a higher boiling point than methane (-97.6°C vs. -161.6°C) due to the stronger intermolecular force of H-bonding in methyl alcohol compared to the London dispersion in methane
• Melting point is the temperature at which a solid becomes a liquid, and it increases as the intermolecular force of attraction becomes stronger, explaining why methyl alcohol (MP=-97.6°C) with H-bonding has a higher melting point than methane (MP= -182°C) with weaker London dispersion
• Surface tension is the energy required to increase the surface area of a liquid by a unit of area, allowing small insects like water striders to walk on water and dried fallen leaves to float on top of the water
• Viscosity is the resistance of a liquid to flow, with honey, syrup, and oil being examples of viscous substances due to their slower flow compared to water
• Vapor pressure is the pressure exerted by a substance in its gaseous state, with liquids having weak intermolecular forces evaporating more easily and having a higher vapor pressure, like acetone (C3H6O) compared to water due to weaker dipole-dipole forces in acetone
• Volatility measures the rate at which a substance vaporizes, with substances like acetone and ethyl alcohol being more volatile than water due to their weaker intermolecular forces of attraction
• Boiling point, melting point, viscosity, and surface tension increase as the strength of intermolecular forces increases, while vapor pressure and volatility decrease with increasing strength of intermolecular forces
• London dispersion forces increase as the molecular mass of a substance increases
• In H-bonding, as the molar mass increases, the boiling point, melting point, viscosity, and surface tension decrease
• Intramolecular forces of attraction exist within each molecule, while intermolecular forces of attraction exist between molecules
• Polar molecules have higher melting points than non-polar molecules due to their stronger intermolecular forces of attraction
• The importance of polarity of molecules on the structure and biological role of cell membranes can be explained based on the Fluid Mosaic Model, which describes the cell membrane as a fluid combination of phospholipids, cholesterol, proteins, and carbohydrates
• The boiling point of water is greater than dihydrogen sulfide (H2S) due to the presence of H-bonding in water
• Vinegar (CH3COOH) is likely to dissolve in water
• Surface tension is the energy required to increase the surface area of a substance by a unit amount
• Nonpolar molecules have low surface tension
• Vinegar (CH3COOH) is miscible in hexane (C6H14)
• Covalent bond is NOT an example of intermolecular forces of attraction
• Boiling point has an indirect relationship with the strength of intermolecular forces of attraction
• Molecular iodine (I2) would be most soluble in carbon tetrachloride (CCl4)
• True: H-bonds are broken when ice melts
• False: Molecules with H-bonds have higher boiling point than molecules with dipole-dipole bond
• False: In covalent molecules, vapor pressure decreases with decreasing strength of intermolecular forces
• True: When the attractive forces holding particles together are greater, a higher temperature is needed to break those forces, resulting in a higher melting point
• True: The strength of dispersion (London) forces tends to increase with increased molecular weight
• Water plays a significant role in the survival of most organisms and various biogeochemical processes on Earth
• Water is a colorless, transparent, odorless liquid that constitutes around 71% of the Earth’s surface and about 60% of the organism’s body

  
• Water plays a significant role in the survival of most organisms and in various biogeochemical processes on Earth