The Chemistry of Life Chapter 2

1. The Chemistry of LifeChapter 2

2. Why should we study chemistry in Biology? Life depends on chemistry!

3. Life depends on chemistry! • When you eat food or inhale oxygen, your body uses these materials in chemical reactions that keep you alive. • Just as buildings are made from bricks, steel, glass, and wood, living things are made from chemical compounds. • Wouldn’t you want an architect to understand building materials? Same idea applies to geneticists, ecologists, zoologists, botanists, biologists, and etc.

4. Atoms • The study of chemistry begins with the basic unit of matter…the History • Greeks were first to try to explain chemical reactions • 400 BC: thought all matter composed of: • Fire • Earth • Water • Air • Democritus first used word “atomos”, meaning indivisible Atom

5. Atoms • Atoms are composed of 3 main particles: (subatomic particles) • Protons (+) • Neutrons • Electrons (-)

6. Protons and Neutrons • Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom. • Both particles have about the same mass.

7. Electrons • Electrons are negatively charged with about 1/1840 the mass of a proton. • They are in constant motion in the space surrounding the nucleus.

8. Atoms • Atoms have equal numbers of electrons and protons. • Because these subatomic particles have equal but opposite charges, atoms are neutral.

10. Elements • Elements are the building blocks of all matter. • Elements cannot be decomposed into simpler matter. Group Number:1 2 3 4 5 6 7 8

11. The Elements • 110 known elements • 88 occur naturally The 110 elements form a plethora of compounds, just as 26 letters of the alphabet make a seemingly endless number of words.

12. Atomic Number Counts the number of protons in an atom

13. 11 Na Atomic Number Symbol Atomic Number on the Periodic Table

14. 11 Na 11 protons Sodium All atoms of an element have the same number of protons

15. Atomic Mass • Mass of an atom. • Approximately equal to the number of protons and neutrons • Find number of neutrons by subtracting the number of protons from the mass.

16. Review: • An element's atomic numbertells how many protons are in its atoms. • An element's mass number tells how many protons and neutrons are in its atoms.

17. Learning Check 1 State the number of protons for atoms of each of the following: A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons C. Barium 1) 137 protons 2) 81 protons 3) 56 protons 2) 7 protons 2) 16 protons 3) 56 protons

18. The Periodic Table

19. Isotopes • Isotopes are atoms that have the same atomic number but different mass number. • Most elements have two or more isotopes. • Same chemical properties because the electron number does not change. What does that mean?

20. Mass number A X Z Atomic number Isotope symbols

21. B 11 5 • How many protons does this have? • How many neutrons does this have? Example • Is the “5” necessary ?

22. More about isotopes: • Some isotopes have unstable nuclei which break down over time. • They are called radioactive isotopes • Some radiation is harmful.

23. Radiation can also be useful Radioactive Dating Tracers with X-rays Cancer Treatment Kill bacteria

24. More About Atomic Structure • The center of the atom is called the nucleus. • Electrons live in something called shells. • Shells are areas that surround the center of an atom. • A shell is sometimes called an orbital or energy level.

25. More About Electrons • Every shell can hold only so many electrons • The further from the nucleus, the more electrons a shell can hold

26. Valence Electrons • The electrons on the outside edge of the atom • This is where the action is- where bonding takes place • Atoms have no more than 8 valence electrons

27. The Octet Rule: • Atoms will combine to form compounds in order to reach eight electrons in their outer energy level.This is very stable! • Atoms with less than 4 electrons tend to lose electrons. • Atoms with more than 4 electrons tend to gain electrons.

28. Chemical Formulas are used to represent compounds Compound • Two or more elements chemically combined in specific proportions • Examples: • Water H2O • Salt NaCl • Sugar C6H12O6 • Two types of compounds: • Ionic • Covalent

29. Ionic Compounds • Form when electrons are transferred from one atom to another. Ions - Atoms with a net charge due to gaining or losing electrons • Gaining electrons gives an ion a negative charge • Losing electrons gives an ion a positive charge **If they have to choose, atoms would rather be stable (with a full “octet”) than neutral.

30. How Does This Happen? Some atoms have a few too many electrons Some atoms only need a few electrons

31. What do you do if you are a sodium (Na) atom with one extra electron? Go look for an atom that wants it!

32. Ionic Bonding • Negative ions and positive ions are held together by ionic bond.

33. Ionic compounds form between metals and nonmetals

34. What If No One Will Give Up An Electron? • Atoms with less than 8 valence electrons can move close to each other and share their electrons • The electrons spend their time around both atoms. • And they lived happily ever after!

35. Covalent Bonds • Formed when a pair of electrons is shared between two atoms. • Sometimes the atoms share two pairs of electrons and form a double bond, or three pairs of electrons to form a triple bond. • Structures formed by covalent bonds are molecules.

36. Covalent compounds form between 2 nonmetals

37. Van der Waals Forces • There are small attractive forces between all atoms • Help to hold molecules to each other • Ex: Gecko

38. Why do compounds form? Let’s summarize what we know! • Atoms are trying to get 8 valence electrons How do compounds form? • By ionic (e- transfer) or covalent (e- sharing) bonding How can you tell if a compound is ionic or covalent? • By the types of elements in the compound (ionic = M + M covalent = M + NM)

39. Learning Check 2: Indicate whether a bond between the following would be 1) Ionic 2) covalent ___ A. sodium and oxygen ___ B. nitrogen and oxygen ___ C. phosphorus and chlorine ___ D. calcium and sulfur ___ E. chlorine and bromine

40. 2-2 Water is a Polar Molecule • Polar: Molecule in which electrons are shared unevenly between atoms, causing each end of the molecule to have a slight charge Negative end Positive end

41. This causes water to be attracted to other polar or charged particles • Water is attracted to ions • Water is attracted to itself, forming hydrogen bonds

42. Hydrogen Bonds In Water Are Responsible For: • Adhesion • Attraction between molecules of different substances • Graduated cylinder • Cohesion • Attraction between molecules of the same substance • Drops of water on a penny • Ex: Surface Tension • Jesus Lizard

43. Types of Chemical Substances • Compounds and Elements are called pure substances. • Most matter is neither of these.

44. Mixtures • Mixtures are combinations of substances held together by physical forces, not chemical bonds. • Each substance keeps its own properties

45. Mixtures may be either: • Solutions • Colloids • Suspensions

46. Solutions • Have small particles • Are transparent (not the same as colorless) • Do not separate • Water solutions are very common in biological systems • Examples: salt water, kool-aid, air, brass, vinegar

47. Colloids • Have medium size particles • Do not separate • Examples: fog, whipped cream, milk, cheese, mayonnaise

48. Suspensions • Have very large particles • Settle out (separates into layers) • Examples: blood platelets, muddy water, calamine lotion, oil & water, Italian salad dressing

49. pH Scale • Measures concentration of hydrogen ions in a solution • Ranges from 0 to 14 • 7 is neutral • 0-7 have more hydrogen ions (H+) and are acidic • 7-14have more hydroxide ions (OH-) and are basic

50. Acids, Bases, and pH • Water molecules form ions • H2O H+ + OH- • Water hydrogen ion + hydroxide ion • Very few ions are formed in pure water, but there are equal numbers of hydrogen and hydroxide ions • Water is neutral!