1. Chemistry of Life

2. Chemistry Life depends on chemistry Life depends on chemistry Living things are made from chemical compounds Living things are made from chemical compounds Inside cells there are continuous chemical reactions taking place that are necessary for survival Inside cells there are continuous chemical reactions taking place that are necessary for survival

3. Review Atom – basic unit of matter Atom – basic unit of matter –Made up of  Protons – positive in the nucleus  Neutrons – neutral in the nucleus  Electrons – negative in a cloud around the nucleus –Very little mass Atoms are neutral: protons = electrons Atoms are neutral: protons = electrons

4. Isotopes Atoms of the same element that have different numbers of neutrons Atoms of the same element that have different numbers of neutrons –Similar chemical properties –Identified by mass number (p+n)

5. Radioactive Isotopes Have unstable nucleus and break down releasing radiation Have unstable nucleus and break down releasing radiation Can be used for Can be used for –Determining age of rocks and fossils –Treating cancer and killing bacteria –Tracers to follow substances in the body

6. Elements Element – pure substance that cannot be broken down Element – pure substance that cannot be broken down –92 natural elements –About 25 essential to life –C, O, H, and N make up 96% of living matter

7. Other elements ElementSymbol % human body weight CalciumCa1.5 PhosphorusP1.0 PotassiumK0.4 SulfurS0.3 SodiumNa0.2 ChlorineCl0.2 MagnesiumMg0.1

8. Molecules and Compounds Molecule – two or more atoms bonded Molecule – two or more atoms bonded –H 2, O 2, NaCl Compound – two or more elements combined in definite proportions Compound – two or more elements combined in definite proportions –H 2 O, NaCl, C 6 H 12 O 6 Remember…..All compounds are molecules, but not all molecules are compounds Remember…..All compounds are molecules, but not all molecules are compounds

9. Chemical Bonds Bond formation involves valence electrons – those farthest away and most loosely held Bond formation involves valence electrons – those farthest away and most loosely held There are two main bond types: electrons are transferred or electrons are shared There are two main bond types: electrons are transferred or electrons are shared

10. Ionic Bonds The attraction between oppositely charged ions The attraction between oppositely charged ions One or more electrons are transferred to another atom One or more electrons are transferred to another atom –Creates ions when electrons are lost or gained Example is NaCl  Na (+) loses and Cl (-) gains Example is NaCl  Na (+) loses and Cl (-) gains

11. Covalent Bonds Electrons are shared between atoms Electrons are shared between atoms –Single: share two electrons –Double: share four electrons The moving electrons The moving electrons actually travel in the orbitals of both atoms Example is water H 2 O Example is water H 2 O

13. Polar Molecules Some atoms have stronger attraction for electrons Some atoms have stronger attraction for electrons The sharing in covalent bonds is not always equal The sharing in covalent bonds is not always equal Creates polar molecules Creates polar molecules

14. Hydrogen Bonds Weak chemical bonds Weak chemical bonds Occurs between polar molecules with hydrogen Occurs between polar molecules with hydrogen Example: the bonds between water molecules Example: the bonds between water molecules

15. Properties of Water Due to hydrogen bonding, water expands when is freezes Due to hydrogen bonding, water expands when is freezes –This makes it less dense, thus ice floats

16. Water makes a great solvent and dissolves many other substances Water makes a great solvent and dissolves many other substances –Solvent – does the dissolving  Usually water or other liquid –Solute – gets dissolved  Example: salt or sugar Polar molecules and ionic compounds usually dissolve easily in water to make a solution Polar molecules and ionic compounds usually dissolve easily in water to make a solution

17. Water is polar – –Oxygen has a stronger attraction for electrons so it “hogs” them – –This makes oxygen more negative and the hydrogens more positive – –This allows for hydrogen bonding and contributes to other properties

18. Cohesion – the attraction of a molecule to like molecules (can stick to itself) – –Allows water to be pulled upward in plants and creates surface tension

19. Adhesion – the attraction of molecules to other substances – –Causes water to rise in a tube – capillary action – –Also help in water transport of plants

20. pH – measures H+ ion concentration Pure water is neutral (pH of 7) – –H+ ions = OH- ions Acids – release H+ ions in solution – –Have pH < 7 – –H+ ions > OH- ions Bases – releases OH- ions in solution – –Have pH > 7 – –H+ ions < OH- ions

21. Buffers Weak acids or bases that can react with stronger substances to prevent sudden changes in pH Act to neutralize a solution and maintain stable conditions