1. Albia Dugger Miami Dade College Cecie Starr Christine Evers Lisa Starr www.cengage.com/biology/starr Chapter 2 Life’s Chemical Basis (Sections 2.1 - 2.3)

2. 2.1 Mercury Rising Fish, shellfish and humans contain toxic methylmercury, which easily crosses skin and mucous membranes to damage the nervous system, brain, kidneys, and other organs Methylmercury comes largely from human activities that release atoms of mercury into the air, such as burning coal

3. Mercury Pollution Coal-fired power plants: the main source of mercury pollution

4. 2.2 Start With Atoms At life’s first level of organization, atoms interact with other atoms to form molecules The properties of molecules depend on, but differ from, those of their atomic components The behavior of elements, which make up all living things, depends on the structure of individual atoms

5. Key Terms atom Particle that is a fundamental building block of all matter element A pure substance that consists only of atoms with the same number of protons

6. Structure of an Atom Atoms consist of electrons (negative charge) moving about a nucleus of protons (positive charge) and neutrons (uncharged)

7. Key Terms nucleus Core of an atom; occupied by protons and neutrons proton Positively charged subatomic particle that occurs in the nucleus of all atoms neutron Uncharged subatomic particle in the atomic nucleus

8. Key Terms charge Electrical property Opposite charges attract, and like charges repel electron Negatively charged subatomic particle that occupies orbitals around an atomic nucleus

9. Elements The number of protons in the nucleus defines the element The periodic table lists elements in order of atomic number Elements in columns behave in similar ways

10. Key Terms atomic number Number of protons in the atomic nucleus; determines the element periodic table Tabular arrangement of known elements by atomic number

11. The Periodic Table

12. ANIMATION: Electron distribution

13. Isotopes Isotopes are atoms of an element that differ in mass number isotopes Forms of an element that differ in the number of neutrons their atoms carry mass number Total number of protons and neutrons in the nucleus of an element’s atoms

14. Radioisotopes Atoms of radioisotopes spontaneously emit subatomic particles or energy by the process of radioactive decay, which can transform one element onto another Researchers use radioisotopes to make tracers that track biological processes inside living organisms

15. Key Terms radioisotope Isotope with an unstable nucleus radioactive decay Process by which atoms of a radioisotope emit energy and/or subatomic particles when their nucleus spontaneously disintegrates tracer Molecule labeled with a detectable substance

16. Medical Radioisotopes Positron-emission tomography (PET scan) used to track processes in the body PET scan of lungs

17. Fig. 2.4, p. 25 Smoker brain lungs heart liver kidneys Non-smoker

18. ANIMATION: 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 HERECLICK HERE

19. Key Concepts Atoms and Elements Atoms, the building blocks of all matter, differ in their numbers of protons, neutrons, and electrons

20. 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 A typical atom has the same number of electrons as protons

21. Energy Levels Up to two electrons occupy each orbital (volume of space) around a nucleus Which orbital an electron occupies depends on its energy

22. Shell Models Shell models help us visualize how electrons populate atoms from the innermost shell outward Concentric circles represent successive energy levels 1st shell: up to 2 electrons 2 nd shell: up to 8 electrons 3 rd shell: up to 8 electrons

23. Shell Models

24. Fig. 2.5, p. 26 6 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. neon (Ne)second shellcarbon (C)oxygen (O) 8 10 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. third shellargon (Ar)chlorine (Cl)sodium (Na) 18 1711 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. first shell hydrogen (H) helium (He) 1 1 proton 1 electron 2 Stepped Art Shell Models

25. ANIMATION: Shell models of common elements 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 HERECLICK HERE

26. Atoms and Ions An atom is most stable when it has no vacancies Atoms fill vacancies by gaining or losing electrons, or by sharing electrons with other atoms An atom with a different number of electrons and protons carries a charge, and is called an ion

27. Swapping Electrons Electronegativity is a measure of how strongly an atom attracts electrons from other atoms An atom that gains an electron is a negative ion An atom that loses an electron is a positive ion

28. Ion Formation

29. Fig. 2.6, p. 27 A A chlorine atom (Cl) becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell. electron gainelectron loss 11p+ 11e– __________ charge: 0 Chlorine atom 17 11 17p+ 18e– ___________ charge: –1 Chlorine ion Sodium atom 17p+ 17e– _________ charge: 0 Sodium ion 11p+ 10e– _________ charge: +1 B A sodium atom (Na) becomes a positively charged sodium ion (Na+) when it (Cl–) when it gains an electron loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies. Ion Formation

30. Fig. 2.6a, p. 27 electron gain Chlorine atom 17 17p+ 18e– ___________ charge: –1 Chlorine ion 17p+ 17e– _________ charge: 0 A A chlorine atom (Cl) becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell. Ion Formation

31. Fig. 2.6b, p. 27 electron loss 11p+ 11e– __________ charge: 0 11 Sodium atom Sodium ion 11p+ 10e– _________ charge: +1 B A sodium atom (Na) becomes a positively charged sodium ion (Na+) when it (Cl–) when it gains an electron loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies. Ion Formation

32. A A chlorine atom (Cl) becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell. electron gain 17 17p+ 18e– ___________ charge: –1 Chlorine ion electron loss 11 Sodium ion 11p+ 10e– _________ charge: +1 B A sodium atom (Na) becomes a positively charged sodium ion (Na+) when it (Cl–) when it gains an electron loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies. Fig. 2.6, p. 27 11p+ 11e– __________ charge: 0 11 Sodium atom Chlorine atom 17 17p+ 17e– _________ charge: 0 Stepped Art Ion Formation

33. ANIMATION: 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 HERECLICK HERE

34. Key Terms shell model Model of electron distribution in an atom ion Charged atom electronegativity Measure of the ability of an atom to pull electrons away from other atoms

35. Sharing Electrons A chemical bond is an attractive force that unites two atoms as a molecule A compound is a molecule that consists of two or more elements A mixture is an intermingling of substances

36. Key Terms chemical bond An attractive force that arises between two atoms when their electrons interact molecule Group of two or more atoms joined by chemical bonds

37. Key Terms compound Type of molecule that has atoms of more than one element mixture An intermingling of two or more types of molecules A liquid mixture is a solution

38. Key Concepts Why Electrons Matter How an atom interacts with other atoms depends on the number and arrangement of its electrons

39. ANIMATION: 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 HERECLICK HERE

40. ANIMATION: 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 HERECLICK HERE

41. ANIMATION: Electron arrangements in atoms 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 HERECLICK HERE