1. The Chemical Context of Life chapter 2

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3. Energy & Matter Universe is composed of 2 things …… Universe is composed of 2 things …… Energy Energy  Ability to do work o Force on an object that causes it to move Matter Matter  Anything that has mass and occupies space  Atoms/elements 3

4. 4 Elements and Compounds Element -- cannot be broken down to other substances by ordinary physical or chemical means Element -- cannot be broken down to other substances by ordinary physical or chemical means Compound -- consists of two or more elements in a fixed ratio Compound -- consists of two or more elements in a fixed ratio

5. Essential Elements of Life Around 25 elements are essential to life Around 25 elements are essential to life C, H, O, and N -- 96% of living matter C, H, O, and N -- 96% of living matter Ca, P, K, and S -- most of the rest Ca, P, K, and S -- most of the rest Trace elements -- required by an organism in minute quantities Trace elements -- required by an organism in minute quantities 5

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7. 7 An atom is the smallest unit of matter that still retains the properties of an element

8. 8 Subatomic Particles Atoms -- subatomic particles Atoms -- subatomic particles  Neutrons (no electrical charge)  Protons (positive charge)  Electrons (negative charge)  Nucleus -- Neutrons and protons  Electrons -- cloud around nucleus  Mostly empty space

9. LE 2-4 Nucleus Electrons Cloud of negative charge (2 electrons)

10. 10 Site: colonial.net

11. Physicist Brian Greene puts it in these terms ….. 11 http://io9.com/a-friendly-reminder-that-you-are-mostly-nothing-471778130

12. LE 2-8 First shell Hydrogen 1 H Lithium 3 Li Second shell Third shell Sodium 11 Na Beryllium 4 Be Magnesium 12 Mg Boron 5 B Aluminum 12 Al Silicon 14 Si Carbon 6 C Nitrogen 7 N Phosphorus 15 P Oxygen 8 O Sulfur 16 S Chlorine 17 Cl Fluorine 9 F Neon 10 Ne Argon 18 Ar Helium 2 He Atomic number Element symbol Electron-shell diagram Atomic mass 2 He 4.00

13. 13 Atomic Number & Atomic Mass Atoms -- differ in number of subatomic particles Atoms -- differ in number of subatomic particles  atomic number -- number of protons  mass number -- protons + neutrons  atomic mass -- approximated by the mass number (mass number + electrons) o Mass electron … 0.000544

14. 14 Atoms and Isotopes Atoms -- differ in number of subatomic particles Atoms -- differ in number of subatomic particles  NOTE: atoms: protons == electrons Isotopes -- two atoms of an element that differ in number of neutrons Isotopes -- two atoms of an element that differ in number of neutrons  Stability/ radioactivity

15. 15 Electron Configuration and Chemical Properties Distribution of electrons in electron shells determines behavior Distribution of electrons in electron shells determines behavior The periodic table shows electron distributions The periodic table shows electron distributions Elements in common rows and/or columns similar properties Elements in common rows and/or columns similar properties

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17. 17 Electron Orbitals three-dimensional space where electrons are (90%) three-dimensional space where electrons are (90%) each shell -- specific number and kind of orbitals each shell -- specific number and kind of orbitals

18. LE 2-9 Electron orbitals Electron-shell diagrams 1s orbital2s orbitalThree 2p orbitals1s, 2s, and 2p orbitals First shell (maximum 2 electrons) Second shell (maximum 8 electrons) Neon, with two filled shells (10 electrons) x z y

19. 19 Valence electrons – outermost level or “shell” Valence electrons – outermost level or “shell” Chemical behavior -- valence electrons Chemical behavior -- valence electrons Interactions – chemical bonds Interactions – chemical bonds  Complete Valence Shell – 8 electrons  Atoms with incomplete valence shells – sharing/transferring valence electrons Valence Electrons

20. Water (H 2 O) Oxygen (O 2 ) 20

21. 21 Molecule -- two or more atoms held together by chemical bonds Single bond = sharing of one pair of valence electrons Single bond = sharing of one pair of valence electrons Double bond = sharing of two pairs of valence electrons Double bond = sharing of two pairs of valence electrons Triple bond = Triple bond =

22. 22 Characteristic Bonding Patterns

23. 23 1 234 5 6 7 8

24. 24 Types of Bonds Strong Chemical Bonds Strong Chemical Bonds  Covalent Bonds  Ionic Bonds Weak Bonds Weak Bonds  Hydrogen Bonds  Van der Waals Forces

25. 25 Covalent Bonds Sharing valence electrons Sharing valence electrons Part of each atom’s valence shell Part of each atom’s valence shell Hydrogen atoms (2 H) Hydrogen molecule (H 2 )

26. 26 Covalent bonds can form between atoms of the same element or atoms of different elements compound vs molecule

27. 27 Electronegativity -- measure an atom’s attraction for electrons in a covalent bond Electronegativity -- measure an atom’s attraction for electrons in a covalent bond  more electronegative -- stronger the pull Polar covalent bond – atoms share the electron unequally -- one atom is more electronegative Polar covalent bond – atoms share the electron unequally -- one atom is more electronegative Nonpolar covalent bond -- atoms share the electron equally Nonpolar covalent bond -- atoms share the electron equally Covalent Bonds

28. LE 2-12 H O H H2OH2O ++ ++ ––

29. 29 Ionic Bonds Ion – unequal numbers of electrons and protons Ion – unequal numbers of electrons and protons  Anion -- negatively charged ion  Cation -- positively charged ion Ionic bond -- attraction between an anion and a cation Ionic bond -- attraction between an anion and a cation

30. 30 Ionic Bonds Highly reactive atoms sometimes strip electrons from their bonding partners Highly reactive atoms sometimes strip electrons from their bonding partners NaCl -- transfers electrons NaCl -- transfers electrons Na Sodium atom (an uncharged atom) Cl Chlorine atom (an uncharged atom) Na + Sodium ion (a cation) Cl – Chlorine ion (an anion) Sodium chloride (NaCl) Na Sodium atom (an uncharged atom) Cl Chlorine atom (an uncharged atom) Na + Sodium ion (a cation) Cl – Chlorine ion (an anion) Sodium chloride (NaCl)

31. 31 Compounds formed by ionic bonds are called ionic compounds, or salts Compounds formed by ionic bonds are called ionic compounds, or salts Salts, such as sodium chloride (table salt), are often found in nature as crystals Salts, such as sodium chloride (table salt), are often found in nature as crystals

32. 32 Free Radicals Molecule whose atoms have one or more unpaired electrons in their outer shells Molecule whose atoms have one or more unpaired electrons in their outer shells Highly unstable and reactive Highly unstable and reactive  Steal electrons  Cause cell death Potentially involved in causing heart disease, Alzheimer’s, cancer, and aging Potentially involved in causing heart disease, Alzheimer’s, cancer, and aging Antioxidants (vitamins C and E) render free radicals harmless Antioxidants (vitamins C and E) render free radicals harmless

33. LE 2-12 H O H H2OH2O ++ ++ –– Na Sodium atom (an uncharged atom) Cl Chlorine atom (an uncharged atom) Na + Sodium ion (a cation) Cl – Chlorine ion (an anion) Sodium chloride (NaCl)

34. 34 Weak Chemical Bonds covalent bonds are the strongest covalent bonds are the strongest weak chemical bonds also important weak chemical bonds also important  reinforce shapes  help molecules adhere to each other

35. 35 Hydrogen Bonds Happens between molecules Happens between molecules a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom in a different molecule a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom in a different molecule In living cells, the electronegative partners are usually oxygen or nitrogen atoms In living cells, the electronegative partners are usually oxygen or nitrogen atoms

36. LE 2-15 –– Water (H 2 O) Ammonia (NH 3 ) Hydrogen bond ++ ++ –– ++ ++ ++

37. 37 Van der Waals Interactions Molecules or atoms that are very close together can be attracted by fleeting charge differences Molecules or atoms that are very close together can be attracted by fleeting charge differences These weak attractions are called van der Waals interactions These weak attractions are called van der Waals interactions

38. 38 Collectively, such interactions can be strong, as between molecules of a gecko’s toe hairs and a wall surface Van der Waals Interactions

39. 39 Common Bonds

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43. 43 Chemical reactions make and break chemical bonds Chemical reactions lead to new arrangements of atoms Chemical reactions lead to new arrangements of atoms The starting molecules of a chemical reaction are called reactants The starting molecules of a chemical reaction are called reactants The final molecules of a chemical reaction are called products The final molecules of a chemical reaction are called products Reactions must balance Reactions must balance

44. 44 Photosynthesis is an important chemical reaction Photosynthesis is an important chemical reaction Sunlight powers the conversion of CO 2 and H 2 O to glucose (C 6 H 12 O 6 ) and O 2 Sunlight powers the conversion of CO 2 and H 2 O to glucose (C 6 H 12 O 6 ) and O 2

45. LE 2-UN44 ReactantsReactionProducts 2 H 2 OO2O2 2 H 2

46. 46 Some rxns “go to completion” -- All reactants converted to products Some rxns “go to completion” -- All reactants converted to products Many rxns reversible: Products of the forward reaction become reactants for the reverse reaction Many rxns reversible: Products of the forward reaction become reactants for the reverse reaction  CaCO 3 ↔ CaO + CO 2 Chemical Equilibrium is reached when the forward and reverse reaction rates are equal Chemical Equilibrium is reached when the forward and reverse reaction rates are equal Reactions Differ

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48. http://www.bbc.co.uk/news/uk-england-leeds- 11959381 http://www.bbc.co.uk/news/uk-england-leeds- 11959381 48