Chemicals of Life

1. Chemicals of Life

2. Chemistry • chemicals give cells properties of life • must know principles of chemistry to understand biology • organisms-bags of chemicals • structuredetermines function • Hierarchy • chemicalsorganellescellstissuesorgansorganisms

3. Matter • living things are made of matter • anything that occupies space & has mass • composed of elements

4. Elements • substances which cannot bedecomposed into simpler substances by chemical means • 92 naturally occurring ones • 25 found in living things • 96%-H, O, C & N • 4%-Ca, P, K & S • trace elements-Fe, Mg, Mn (manganese) & I • called essential • cannot live without them

5. Periodic Table

6. Atoms • elements are composed of atoms • only one kind of atom for each element • smallest units of matter that retain the properties of an element

7. Sub-atomic Particles • Protons • Electrons • Neutrons • different elements have different numbers of sub-atomic particles • chemical & physical differences of elements are due to these differences

8. Sub-Atomic Particles • Protons • one positive charge • found in nucleus of atom • Neutrons • no charge • found in nucleus of atom • Electrons • one negative charge • orbit nucleus

9. Periodic Table • atom’s structure determines how element it comprises forms compounds & molecules • key to this can be found by knowing number of sub-atomic particles an element possess • found in Periodic Table of the Elements

10. atomic number-number in upper left corner • atomic weight or mass number-number located on bottom

11. Atomic Number • gives number of protons in an atom • Helium • Atomic Number = 2 • has 2 protons

12. Mass Number • found by adding number of neutrons & number of protons • He = 4 • some atoms of an element may have different mass numbers • these are isotopes • same number of protons & electrons but different number of neutrons

13. Number of Electrons • net charge of an atom is zero • each proton has one positive charge • each electron has one negative charge • neutrons have no charge • to be neural atom must have the same number of electrons and protons • atom of helium with 2 protons • has 2 electrons

14. Atomic Number • How many protons does Sulfur have? • How many electrons? • Why?

16. Chemical Properties • arrangement of electrons determines chemical properties of an atom • electrons orbit around nucleus • found at different energy levels-shells • each shell accommodates a specific number of electrons

17. Electron Shells • innermost shell-2 • 2nd & 3rd-8 • number of electrons in outermost shell determines chemical properties of atom • those with shells that are not full will interact with other atoms & participate in chemical reactions • those with full shells do not interact-inert

18. Electron Shells • H-only one electron in outer most shell • very reactive • C, N, & O • also highly reactive since outer shells are incomplete • He-inert or nonreactive because outer shell is full

19. Reactivity of Chlorine • Is Chlorine reactive or not reactive? • How can you tell?

20. Atom Interactions-Chemical Bonds • when an atom with an incomplete outer shell reacts with another atom with an incomplete outer shell they can interact or form a bond • Share • Donate • Receiveelectrons • in this way both atoms can have a completed outer shell

21. Types of Chemical Bonds • Covalent Bonds • share electrons • Ionic • give or receive electrons

22. Sodium & Chloride

23. Ionic Bonding

25. Covalent Bonds • 2 atoms with incomplete shells • each share a couple electrons • so at any one time one atom has a completed outer shell • forms molecules

27. In Class Exercise • Pretend you are an atom • Take the number of your birth month as your atomic number • Determine the configuration of electrons in your valence shell • Find another atom that you might interact with to form ions or new molecules • Demonstrate-draw on the board

28. Chemical Reactions • elements combine to make molecules & compounds • 2 H2 + O2 2H2O • 2 molecules of H react with one molecule of O (reactants) to form 2 molecules of water (product) • arrow indicates direction of reaction • two sides of equation on either side of arrow must balance

29. Water • single most important constituent of body • life on Earth depends on unusual structure & nature of water

30. Importance of Water • Organisms consist mostly of water • 2/3rds total body weight of humans • Biochemistry is a wet chemistry • biological molecules do not react chemically unlessin solution • Water is an important reactant • nearly allchemical reactions in the body occur in water • Foods are digested to their building blocks by decomposition reactions called hydrolysis • involves addition of water • When large molecules form from smaller ones, water is removed in dehydration synthesisor condensation reactions

31. Water Structure • 2 H atoms attached covalentlyto one O2 molecule • sharing of electrons is not equal • oxygen pulls more on electrons than does hydrogen • electrons spend more time near oxygen than hydrogen • unequal sharing produces- polar bond • Nonpolar bond • bonds in which two atoms involved have an equal pull on electrons

32. Water Structure • O2 attracts electrons more strongly than H-giving water an asymmetrical distribution of charge • result-V-shape • H end has positive charge • Oxygen end has negative charge • water has 2 poles-polar • polarity results in weak electrical attractions between neighboring water molecules

33. Polarity of Water • Polarity results in weak electrical attraction between neighboring water molecules • slightly positive Hs in one water molecule attract slightly negatively charged O2 in another water molecule • opposite electrical charges attract • water molecules attract each othermaking water kind of sticky • these weak attractions-hydrogen bonds • much weaker than covalent or ionic bonds

34. Polarity, H Bonding & Water’s Properties • cohesive nature • ability to moderate temperature • ice floating • universal solvent properties

35. Dissociation • compounds formed by ionic bonds will ionizeor dissociate in water • dissociation produces cations(+) & anions(-) • aqueous solution containing anions & cations will conduct electrical currents • cations move to negative side having a + change & anions move to positive side having a – charge • soluble inorganic molecules whose ions will conduct an electrical current in solution are called electrolytes • NaCl is an electrolyte • NaCl + H2ONa+ + Cl-

36. Acids • H+ & OH- are in solutions at all times • H2O <-------> H+ + OH- -reversible reaction • some compounds add more hydrogen ions • others remove them • compound that donates hydrogen ion-acid • HClH+ + Cl- • acidic solution is one that has more H+ than OH-

37. Bases • compound that accepts or removes hydrogen ions is a base • NaOHNa+ +OH- • basic solution- has more OH- than H+

38. pH scale • pH = potential hydrogen • scale developed in 1909 by Dane Soren Sorensen • beer brewer looking for a way to check acidity of beer • describes how acidic or basic a solution is • scale ranges from 0-14 • 0 = most acidic • 14 = most basic • 7=neutral

39. pH • at neutral pH • H+ = OH- • pH < 7 is acidic • pH > than 7 is more basic or alkaline

40. Buffers • pH of blood ranges between 7.35-7.45 • value must be maintained in narrow range • even small change can lead to severe metabolic consequences • biological fluids contain buffers • substances that resist changes in pH by accepting H+ when in excess & donating H+ when depleted