1. The Chemical Basis of Life Chapter 2

2. Structure of Matter 2 Matter – anything that takes up space and has mass (weight). It is composed of elements. Elements – composed of chemically identical atoms: Bulk elements – required by the body in large amounts Trace elements - required by the body in small amounts Ultratrace elements – required by the body in very minute amounts Atoms – smallest particle of an element

3. Elements 3

4. Compounds Are composed of 2 or more elements in a fixed ratio The properties differ from those of individual elements Example:

5. Atomic Structure 5 Atoms - composed of subatomic particles: Proton – carries a single positive charge Neutron – carries no electrical charge Electron – carries a single negative charge Nucleus Central part of atom Composed of protons and neutrons Electrons move around the nucleus Electron (e – ) Lithium (Li) Proton (p + ) Neutron (n 0 ) Nucleus 0 0 + + 0 + 0 - - - Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

6. ATOMIC STRUCTURE the number of protons in an atom the number of protons and neutrons in an atom He 2 4 Atomic mass Atomic number In a neutral atom the number of electrons = number of protons

7. Energy Levels 7 The exact location of an electron can’t be identified at any given time. We use the Bohr Model to illustrate the most probable location of electrons at any given time. Electrons in the outer ring are called valence electrons. Octet Rule – atoms gain, lose or share electrons to gain a full set of valence electrons (8) Electron (e – ) Lithium (Li) Proton (p + ) Neutron (n 0 ) Nucleus 0 0 + + 0 + 0 - - -

8. Isotopes of Carbon How do these differ? What is an isotope?

9. Ionic Bonding Ionic bonds form when atoms give and take valence electrons.

10. Bonding of Atoms: Ions 10 Ion An atom that gains or loses electrons to become stable An electrically charged atom Cation A positively charged ion Formed when an atom loses electrons Anion A negatively charged ion Formed when an atom gains electrons 11p + 12n 0 Sodium atom (Na)Chlorine atom (Cl) (a) Separate atoms If a sodium atom loses an electron to a chlorine atom, the sodium atom becomes a sodium ion (Na + ), and the chlorine atom becomes a chloride ion (Cl – ). 17p + 18n 0

11. Covalent Bonding Covalent bonds form when atoms share electrons to form a full number of valence electrons.

12. 12 Covalent Bonds Hydrogen atoms form single bonds Oxygen atoms form two bonds Nitrogen atoms form three bonds Carbon atoms form four bonds H ― H O = O N ≡ N O = C = O Hydrogen atom+ H Hydrogen molecule H2H2 Hydrogen atom H ++ ++ -- - - Atoms share electrons in covalent bonds.

13. Bonding of Atoms: Polar Molecules 13 Polar Molecules When electrons are not shared equally in covalent bonds Molecule with a slightly negative end and a slightly positive end Water is an important polar molecule Slightly negative end Slightly positive ends (a) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

14. Hydrogen Bonds 14 Hydrogen Bonds A weak attraction between the positive end of one polar molecule and the negative end of another polar molecule Formed between water molecules Important for protein and nucleic acid structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H H H H H H H H H H O O O O O Hydrogen bonds (b)

15. Van der Waals Forces When atoms or molecules have attractive or repelling forces that are not due to ionic or covalent bonds. http://www.ted.com/talks/robert_full_learning _from_the_gecko_s_tail.html

16. Chemical Reactions 16 Chemical reactions occur when chemical bonds form or break among atoms, ions, or molecules. Based on valence electrons Reactants are the starting materials of the reaction - the atoms, ions, or molecules Products are substances formed at the end of the chemical reaction NaCl  Na + + Cl - ReactantProducts

17. 17 Types of Chemical Reactions Synthesis Reaction – more complex chemical structure is formed A + B  AB Decomposition Reaction – chemical bonds are broken to forma simpler chemical structure AB  A + B Exchange Reaction – chemical bonds are broken and new bonds are formed AB + CD  AD + CB Reversible Reaction – the products can change back to the reactants A + B AB

18. Metabolism All of the chemical reactions occurring in the cells of the body. – Catabolism – breaks down large food molecules into smaller chemicals This causes energy to be released – Anabolism – builds larger more complex molecules from smaller molecules This requires energy

19. Organic and Inorganic Molecules Organic Molecules – Contain C-C bonds or C-H bonds or both – Generally large and more complex then inorganic molecules Inorganic Molecules – Do not contain C-C bonds or C-H bonds

20. 20 Inorganic Substances Water Most abundant compound in living material Two-thirds of the weight of an adult human Major component of all body fluids Medium for most metabolic reactions Important role in transporting chemicals in the body Absorbs and transports heat

21. Properties of Water Water is cohesive. Water acts as a lubricant or cushion to protect against damage from friction or trauma

22. Water as a Solvent Water is a great solvent. Many kinds of molecules can dissolve in cells providing for transportation or chemical reactions

23. Water and Temperature Water has a high specific heat. The hydrogen bonds absorb heat when they break and release heat when they form –This minimizes temperature change –Body temperature remains fairly constant

24. Water and Evaporation Water has a high heat of vaporization. Many hydrogen bonds must be broken when water evaporates. –This takes energy –Evaporation of perspiration cools the body

25. 25 Inorganic Substances Carbon dioxide (CO 2 ) Waste product released during metabolic reactions Must be removed from the body Helps maintain appropriate acid-base balance Inorganic salts Abundant in body fluids Sources of necessary ions (Na +, Cl -, K +, Ca 2+, etc.) Play important roles in metabolism Oxygen (O 2 ) Used by cells to release energy from nutrients Necessary for survival

26. 26 Acids, Bases, and Salts Electrolytes – substances that release ions in water Acids – electrolytes that dissociate to release hydrogen ions in water (proton donor) HCl  H + + Cl - Bases – substances that release ions that can combine with hydrogen ions (proton acceptor) NaOH  Na + + OH - Salts – electrolytes formed by the reaction between an acid and a base NaCl  Na + + Cl - HCl + NaOH  H 2 O + NaCl

27. 27 Acid and Base Concentration pH scale - indicates the concentration of hydrogen ions in solution Neutral – pH 7; indicates equal concentrations of H + and OH - Acidic – pH less than 7; indicates a greater concentration of H + Basic or alkaline – pH greater than 7; indicates a greater concentration of OH - OH – concentration increasesH + Acidic H + Relative Amounts of H + (red) and OH – (blue) Basic OH – 2.0 gastric juice 6.0 corn 7.0 Distilled water 8.0 Egg white 10.5 milk of magnesia 11.5 Household ammonia pH01234567891011121314 Basic (alkaline)Neutral Acidic 3.0 apple juice 4.2 tomato juice 5.3 cabbage 6.6 cow’s milk 7.4 Human blood 8.4 Sodium biocarbonate Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.