1. Bonding and Water Properties General Biology

2.  A chemical compound consists of atoms of two or more elements  Compounds are held together by chemical bonds Chemical Compounds

3.  Chemical bonds  Forces of attraction that hold atoms of a compound together  The three types of bonds are:  Covalent bonds  Ionic bonds  Hydrogen bonds Bonding

4.  Covalent bonds  Share electrons between atoms  Each atom has a filled outer energy level  2 types of covalent bonds  Nonpolar covalent – electrons are shared equally  Example: Oxygen gas  Polar covalent – electrons are shared unequally and pulled towards one atom making a neg. charge, or pole, at one end of the atom  Example: Water Bonding

5. Covalent bonds

6. Covalent bonds can be nonpolar or polar

7.  Form between a positive ion and a negative ion Example: Na+ and Cl- bond to create NaCl Ionic Bonds

8. Ionic bonding

9.  Hydrogen bonds  Weak bonds between molecules  Positively charged hydrogen atom in one covalently bonded molecule is attracted to a negatively charged area of another molecule.  Example: Hydrogen bonding between water molecules Hydrogen Bonding

10. Hydrogen bonding

11.  Because of hydrogen bonding, water has some very unique properties. Water

12. Fig. 3-2 Hydrogen bond  – – H  + + H O — —  + +  + +  + +  – –  – –  – –

13.  Water exists in 3 forms: gas, liquid, or solid  Hydrogen bonds are formed or broken as water changes state Water Properties

14.  Ionic and polar substances dissolve well in water b/c of water’s hydrogen bonds.  Water facilitates chemical reactions  Hydrophilic substances—interact readily with water, such as table salt  Hydrophobic substances—not disrupted or dissolved by water, such as fats Water is an excellent solvent.

15. Fig. 3-7 Cl – Na Cl – + + + + + + + + – – – – – – – – Na + – – – +

16.  Changes temperature very slowly.  Must add a lot of energy to heat or remove a lot of energy to cool/freeze water. Water has a high heat capacity

17.  Less dense as a solid than a liquid… due to hydrogen bonding Ice floats!

18. Fig. 3-6a Hydrogen bond Liquid water Hydrogen bonds break and re-form Ice Hydrogen bonds are stable

19.  Cohesion – attraction between like substances  Occurs b/c of hydrogen bonding between water molecules  Leads to a high surface tension  Creating a water surface that is very firm  Example: insects ‘walking’ on water Water has strong cohesion and high surface tension.

20. Fig. 3-4

21.  Attraction of unlike substances  Capillary action  Water adhering to the narrow tubing or absorbent solids Water has strong adhesion.

22. Fig. 3-3 Water-conducting cells Adhesion Cohesion 150 µm Direction of water movement

23.  http://www.sumanasinc.com/webcontent/animations/ content/propertiesofwater/water.html http://www.sumanasinc.com/webcontent/animations/ content/propertiesofwater/water.html Water Animation