3.1 Chemical elements & water

1. 3.1 Chemical elements & water IB Biology

2. Chemistry Recap • Element - pure substance, made of one kind of atom, unique chemical and physical properties • Molecules - two or more atoms chemically combined through a covalent bond • Ion - an atom or molecule with an electric charge

3. Elements • Most common elements in living things • Carbon (C) • Hydrogen (H) • Oxygen (O) • Nitrogen (N) • C, H, N, O found in proteins and nucleic acid (DNA) • C, H, O found in carbohydrates and lipids

4. Elements found in small amounts • Sulfur (S) • Needed for some proteins in all organisms • Form disulphide bonds • Phosphorus (P) • In DNA and ATP • Calcium (Ca/Ca+) • Bone structure, muscle contraction, cell division, regulation of cell processes • Iron (Fe) • Aerobic cellular respiration • Sodium (Na/Na+) • Nerve signals (animals), controls amount of water in cytoplasm

5. Bonding Ionic Bond - Gain / loss of electrons Covalent Bond - Sharing electrons

6. Polar Covalent Bonds Covalent bond - bond within molecule Sometimes atoms in a covalent bond do not share electrons equally. The result is a bond with a slightly positive end and a slightly negative end as seen in water molecules.

7. Hydrogen Bonding in Water Intermolecular force Since water is polar, the positive ends attract the negative ends. This attraction creates hydrogen bonds. Hydrogen bonds are weak individually, but together lead to the unique properties of water

8. Water • H2O - two hydrogen atoms, one oxygen atoms • Molecule formed by polar covalent bond • Unequal sharing of electrons • Forms a charge distribution • Partial positive and partial negative • Hydrogen bond gives water unique properties

9. Properties of Water Surface tension • Cohesion • Water molecules stick to each other due to hydrogen bonds between them

10. Cohesion Activity • Obtain a 1 dirham coin • Use an eyedropper to place water onto coin, 1 drop at a time • Record # of drops and qualitative observation • Repeat with a small amount of dish soap on coin • Discuss results

11. Cohesion - Water used as a transport medium Many substances can be dissolved and therefore carried in water The cohesion of water lets it be pulled to a great height in plants, transporting dissolved substances Water can also transport heat due to its high heat capacity (blood carries from one body part to another, etc.)

12. Properties of Water • Versatile solvent • Because water has areas of partial positive and negative charge, it can dissolve many substances that are polar,positively charged, or negatively charged • Water does NOT dissolve non-polar, uncharged substances (lipids / fats / oils) • Medium for most chemical reactions in living organisms

13. Solvent: Water as a medium for metabolic reactions • Solvent: most reactions of life happen with the substances dissolved in water (cytoplasm is mostly water) • Ex. Oxygen from the air must dissolve into the water on the inside of the lungs • State: the liquid state allows substances to stay in the liquid but move around enough to come in contact and react • Excellent for metabolic reactions

14. Properties of Water • Thermal properties • Heat capacity (high specific heat): large amounts of energy are needed to raise the temperature of water • State changes (high heat of vaporization): water boils at a high temperature and has a large temperature range as a liquid • Evaporative cooling(high heat of vaporization): energy taken to break hydrogen bonds and free water molecules as they evaporate, cools remaining water

15. Thermal properties: Water as a coolant • Evaporative cooling: Terrestrial organisms may sweat or pant to remove excess heat • Heat capacity: Water organisms may transfer heat to the environment without raising the water temperature by much

16. Video • Properties of water • http://www.sumanasinc.com/webcontent/animations/content/propertiesofwater/water.html

17. Homework • Pg 42 Thinking about science