University:
Felician University
Course:
CHEM-105 | Principles of Chemistry
Academic year:

2022
Views:

206

Pages:

1
Author:

Clint W.

Topic 2.2: WATER Water Structure Hydrogen Bonding Water is made up of two hydrogen atoms covalently bonded to an oxygen atom (molecular formula: H2O) The dipolarity of the water molecule enables it to form polar associations with other charged molecules (polar or ionic) Oxygen has a higher electronegativity and attracts the shared electrons more strongly, resulting in polarity Water molecules can also form hydrogen bonds with other water molecules (between an δ+ hydrogen and an δ– oxygen) O H O H Water Structure δ+ H δ– H δ+ Hydrogen bonds Water Polarity Cohesive Properties Solvent Properties Water can form intermolecular associations with other molecules that share common properties (e.g. polarity) Water is commonly referred to as the universal solvent due to its capacity to dissolve a large number of substances (ionic / polar) • Large quantities of water molecules can sufficiently weaken forces (e.g. ionic bonds) and form dispersive hydration shells • Water can form hydrogen bonds with other water molecules (cohesion: like molecules stick together) • Water can form polar associations with charged molecules (adhesion: unlike molecules stick together) Substances that can dissolve in water are called hydrophilic • Includes glucose, amino acids, sodium chloride, oxygen (low) The cohesive properties of water results in a relatively high surface tension (can resist low level external forces) Substances that cannot dissolve in water are called hydrophobic • Includes lipids (fats and cholesterol) The adhesive properties of water allow for potential capillary action (e.g. transpiration stream in plants) These solvent properties make water an important medium for metabolic reactions, as well as a necessary transport medium Thermal Properties Water versus Methane Water has the capacity to absorb large amounts of heat energy before undergoing a resultant change in state • Extensive hydrogen bonding must first be broken Water and methane differ in thermal properties despite having similar structures (comparable weight, size, valence structure) Water therefore has a very high specific heat capacity • Energy required to raise temperature of 1g by 1ºC The differences are due to the polarity of water and its capacity to form intermolecular hydrogen bonds METHANE These properties make water a very effective coolant • Evaporation of sweat requires absorption of heat WATER δ+ δ+ δ– Other Properties Water is transparent, allowing light to pass through it • Important for photosynthesis and also for vision Water expands when frozen, becoming less dense • Important for life on Earth as it means ice floats and the oceans underneath don’t automatically freeze Formula CH4 H2O Polarity Non-polar Polar (J.g–1.ºC–1) 2.20 4.186 Boiling Point (ºC) –161 100 Heat Capacity