General Chem. Review and Water See pages 20-27

Weakest intermolecular – Between molecules Transfer of Electrons Intra- and Inter- molecular Eg. NaCl Sharing of Electrons Intramolecular Eg. CO2, H2O Weakest intermolecular – Between molecules

Be sure to read pp.20-25 in your Inquiry Into Life text (9th ed.). You’ll read about Elements, Atoms, Isotopes, Molecules, Compounds, Ionic and Covalent Rxns, Double and Triple Bonds, and Redox Rxns. All of these serve as a rudimentary review of Jr. Science, Chem. 11, and Chem. 12.

Water Not considered organic (it is inorganic) because it does not contain carbon and hydrogen together. The atoms involved are COVALENTLY bonded (ie. they share electrons). In fact, the bonds are Polar Covalent. Polar covalent implies that the sharing is slightly uneven, thus creating partial charges.

These charges exist as a partial negative charge on the oxygen atom and partial positive charges on each of the the hydrogen atoms. (See fig. 2.8, page 26). This polar nature of water molecules allows for HYDROGEN BONDING (ie. a positively-charged hydrogen atom is electrostatically attracted to a negatively-charged oxygen atom from another water molecule). See fig. 2.8 again. Hydrogen bonds are depicted by dashed lines (unlike ionic/covalent bonds lines which are solid). It takes less energy to break H-bonds (relative to ionic/covalent). In fact, often the KE of the water molecules breaks the H-bonds.

When water is in its liquid form, its hydrogen bonds are very fragile, about 5% as strong as covalent bonds. They form, break, and re-form with great frequency due to the Kinetic Energy of the molecules But, at any instant, a substantial percentage of all the water molecules are bonded to their neighbours, giving water more structure than most other liquids (in fact, the H-bonds keep water a liquid at room temp., not a gas).

Characteristics of Water (Within the Body) Regulates Temperature: Water has a high heat capacity This means that water can absorb a huge amount of heat before it evaporates and it gives off this heat as it cools and nears freezing (but it also cools slowly as it holds heat well). This ability of water to maintain a steady temperature range keeps the body temperature at or around 37.1o C. Sweating to cool as well.

Takes a larger amount of energy to raise the temp Takes a larger amount of energy to raise the temp. of water (only NH3 is higher)

Water is COHESIVE: Due to hydrogen bonds, water has great COHESION, meaning that water molecules that are “ahead” of others in the flow “tug” the others along to allow for a smooth flow. Blood is able to flow smoothly and efficiently through its vessels due to this cohesion. As well, water’s cohesion allows molecules/ions to be evenly distributed throughout (important in blood). Cohesion also plays a role in the ability of plants to transfer water from their roots to their leaves (through xylem vessels against gravity). Blood = 55% plasma + 45% blood cells Plasma = 90% water + 10% dissolved substances. Therefore, blood is 49.5% water (of course, cells are mainly composed of water too!)

Water acts as a LUBRICANT (as it is a liquid at body temp.): Examples: Saliva is water-based and helps to coat food for easier swallowing. Synovial fluid in joints for cushioning and smooth/efficient movement. Tear ducts to produce tears to keep eyes clean. Mucus production to lubricate respiratory tract and to catch debris/pathogens that enter the body. Vaginal/penile secretions for natural lubrication during intercourse.

Acts as a SOLVENT: Water dissolves polar substances due to its polar nature. Polar “likes” polar, so water only dissolves polar solutes. Examples: Na+, Cl-, K+, Ca2+, glucose, amino acids, glycerol, etc. Sometimes, water is referred to as a “universal” solvent since it can dissolve so many substances. This allows plasma to carry useful polar materials dissolved in the water that makes it up. It also increases the efficiency of the chemical reactions that occur in a cell as reactions in the aqueous phase tend to happen faster. Polar = Hydrophilic ; Non-Polar = Hydrophobic