Chapter 2 Life ’ s Chemical Basis

1. Chapter 2Life’s Chemical Basis

2. 2.1 Mercury Rising • Mercury is released into the atmosphere by volcanic activity, and by human activities such as burning coal • Once airborne, mercury can drift long distances before settling to Earth’s surface, where microbes convert it to a toxic substance called methylmercury • Once mercury enters the body, it damages the nervous system, brain, kidneys, and other organs • All human bodies now have detectable amounts of mercury

3. Atmospheric Fallout from Coal-Fired Power Plant Emissions

4. 2.2 Start With Atoms • The behavior of elements, which make up all living things, starts with the structure of individual atoms • The number of protons in the atomic nucleus defines the element, and the number of neutrons defines the isotope

5. Structure of Atoms • Atomsare the building blocks of all substances • Made up of electrons, protons and neutrons • Chargeis an electrical property • Attracts or repels other subatomic particles

6. Characteristics of Atoms • Electrons (e-) have a negative charge • Move around the nucleus • Thenucleuscontains protons and neutrons • Protons(p+)have a positive charge • Neutrons (n) have no charge

7. Characteristics of Atoms • Atoms differ in number of subatomic particles • Atomic number(number of protons) determines the element • Elements consist only of atoms with the same atomic number • Mass number • Total protons and neutrons in a nucleus • Used to identify isotopes

8. Atoms proton neutron electron

9. The Periodic Table • Periodic table of the elements • An arrangement of the elements based on their atomic number and chemical properties • Created by Dmitry Mendeleev

10. Periodic Table of the Elements

11. ANIMATED FIGURE: Atomic number, mass number To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

12. Isotopes and Radioisotopes • Isotopes • Different forms of the same element, with different numbers of neutrons • Some radioactive isotopes – radioisotopes – are used in research and medical applications

13. Radioisotopes • Henri Becquerel discovered radioisotopes of uranium in the late 1800s • Radioactive decay • Radioisotopes emit subatomic particles of energy when their nucleus breaks down, transforming one element into another at a constant rate

14. Radioactive Decay • Example:14C →14N nucleus of 14N, with 7 protons, 7 neutrons nucleus of 14C, with 6 protons, 8 neutrons

15. Tracers • Tracer • Any molecule with a detectable substance attached • Examples: • CO2 tagged with 14C used to track carbon through photosynthesis • Radioactive tracers used in medical PET scans

16. brain lungs heart liver kidneys Non-smoker Smoker Figure 2-4 p25

17. ANIMATED FIGURE: PET scan To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

18. Take Home Message: The basic building blocks of all matter • All matter consists of atoms, tiny particles that in turn consist of electrons moving around a nucleus of protons and neutrons • An element is a pure substance that consists only of atoms with the same number of protons. Isotopes are forms of an element that have different numbers of neutrons • Unstable nuclei of radioisotopes disintegrate spontaneously (decay) at a predictable rate to form predictable products

19. ANIMATION: Subatomic particles To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

20. ANIMATION: Isotopes of hydrogen

21. 2.3 Why Electrons Matter • Atoms acquire, share, and donate electrons • Whether an atom will interact with other atoms depends on how many electrons it has

22. About Vacancies • Electrons move around nuclei in orbitals • Each orbital holds two electrons • Each orbital corresponds to an energy level • An electron can move in only if there is a vacancy • free radical • Atom with an unpaired electron

23. Vacancy/ No Vacancy

24. Why Atoms Interact • Theshell modelof electron orbitals diagrams electron vacancies; filled from inside out • First shell: one orbital (2 electrons) • Second shell: four orbitals (8 electrons) • Third shell: four orbitals (8 electrons) • Atoms with vacancies in their outer shell tend to give up, acquire, or share electrons

25. A The first shell corresponds to the first energy level, and it can hold up to 2 electrons. Hydrogen has one proton, so it has 1 electron and 1 vacancy. A helium atom has 2 protons, 2 electrons, and no vacancies. The number of protons in each model is shown. 1 proton 1 2 1 electron B The second shell corresponds to the second energy level, and it can hold up to 8 electrons. Carbon has 6 protons, so its first shell is full. Its second shell has 4 electrons, and four vacancies. Oxygen has 8 protons and two vacancies. Neon has 10 protons and no vacancies. hydrogen (H) helium (He) first shell 8 6 10 second shell carbon (C) oxygen (O) neon (Ne) C The third shell, which corresponds to the third energy level, can hold up to 8 electrons. A sodium atom has 11 protons, so its first two shells are full; the third shell has one electron. Thus, sodium has seven vacancies. Chlorine has 17 pro tons and one vacancy. Argon has 18 protons and no vacancies. 18 11 17 third shell sodium (Na) chlorine (Cl) argon (Ar) Stepped Art Figure 2-5 p26

26. ANIMATED FIGURE: The shell model of electron distribution To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

27. Atoms and Ions • Ion • An atom with a positive or negative charge due to loss or gain of electrons in its outer shell • Examples: Na+, Cl- • Electronegativity • A measure of an atom’s ability to pull electrons from another atom

28. electron loss electron gain Sodium atom Chlorine atom 11p+ 11e– 17p+ 17e– charge: 0 charge: 0 Chloride ion Sodium ion 11p+ 10e– 17p+ 18e– charge: –1 charge: +1 Figure 2-6 p27

29. ANIMATED FIGURE: Ionic bonding To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

30. Take-Home Message:Why do atoms interact? • An atom’s electrons are the basis of its chemical behavior • Shells represent all electron orbitals at one energy level in an atom; when the outermost shell is not full of electrons, the atom has a vacancy • Atoms with vacancies tend to interact with other atoms

31. 2.4 Chemical Bonds:From Atoms to Molecules • Chemical bonds link atoms into molecules • The characteristics of a chemical bond arise from the properties of the atoms taking part in it

32. Chemical Bonds • Chemical bond • An attractive force existing between two atoms when their electrons interact • Molecule • Two or more atoms joined in chemical bonds

33. Combining Substances • Compounds • Molecules consisting of two or more elements whose proportions do not vary • Example: Water (H2O) • Mixture • Two or more substances that intermingle but do not bond; proportions of each can vary

34. The Water Molecule one oxygen atom two hydrogen atoms

35. Bonds and Electrons • Whether one atom will bond with others depends on the element, and the number and arrangement of its electrons • electronegativity • Measure of the ability of an atom to pull electrons away from other atoms

36. Three Types of Bonds • The characteristics of a bond arise from the properties of the atoms that participate in it • The three most common types of bonds in biological molecules are ionic, covalent, and hydrogen bonds

37. Ionic Bonds • Ionic bond • A strong mutual attraction between two oppositely charges ions with a large difference in electronegativity (no electron transferred) • Example: NaCl (table salt)

38. Ionic Bond: Sodium Chloride ionic bond 11 17 Sodium ion 11p+, 10e– Chloride ion 17p+, 18e–

39. Ionic Bond: Sodium Chloride Cl– Na+

40. Ionic Bond: Sodium Chloride positive charge negative charge

41. ANIMATED FIGURE: How atoms bond To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

42. Covalent Bonds • Covalent bond • Two atoms with similar electronegativity and unpaired electrons sharing a pair of electrons • Can be stronger than ionic bonds • Atoms can share one, two, or three pairs of electrons (single, double, or triple covalent bonds)

43. Characteristics of Covalent Bonds • Nonpolar covalent bond • Atoms sharing electrons equally; formed between atoms with identical electronegativity • Polar covalent bond • Atoms with different electronegativity do not share electrons equally; one atom has a more negative charge, the other is more positive

44. Polarity • Polarity • Separation of charge intodistinct positive and negative regions in a polar covalent molecule • Example: Water (H2O)

45. molecular hydrogen (H2) molecular oxygen (O2) water (H2O) Figure 2-9 p29

46. ANIMATED FIGURE: Covalent bonds

47. Table 2-1 p29

48. Take-Home Message:How do atoms interact in chemical bonds? • A chemical bond forms between atoms when their electrons interact • A chemical bond may be ionic or covalent depending on the atoms taking part in it • An ionic bond is a strong mutual attraction between two ions of opposite charge • Atoms share a pair of electrons in a covalent bond; when the atoms share electrons unequally, the bond is polar

49. 2.5 Hydrogen Bonds and Water • The unique properties of liquid water arise because of the water molecule's polarity • Extensive hydrogen bonds form among water molecules

50. Polarity of the Water Molecule • Overall, water (H2O) has no charge • The water molecule is polar • Oxygen atom is slightly negative • Hydrogen atoms are slightly positive • Hydrogen bonds form between water molecules • Gives water unique properties