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.

4. It all begins with… • Atoms – the smallest unit of matter 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

5. Atoms are composed of 3 main particles: (subatomic particles) • Protons (+) • Neutrons (0) • Electrons (-)

6. Protons and Neutrons • Nucleus – Center of atom that contains protons and neutrons. • Both particles have about the same mass.

7. Electrons • Electrons are about 1/1840 the mass of a proton. • They are in constant motion in the space surrounding the nucleus. • Electron cloud model

8. Atoms have equal numbers of electrons and protons. • This makes an atom neutral

10. The Elements • 116 known elements • 92 occur naturally • Only 25 are important to living organisms!

11. Elements • Atomic number – number of protons • Atomic mass – number of protons and neutrons. (amu) • Atomic symbol – letters naming the element

12. 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

13. The Periodic Table

14. More Electrons • Electrons reside in something called shells. • Shells are areas that surround the center of an atom. (aka. orbitals and energy levels)

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

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

18. 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.

19. Review • How many protons, electrons, and neutrons are in… • Boron • Chlorine • Sodium • How many valence electrons does each of these elements have? • What is the chemical formula for water?

20. 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

21. Ionic Compounds • Form when electrons are transferred from one atom to another. (stealing) 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.

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

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

24. Ionic Bonding • Negative ions and positive ions are held together by ionic bond. • https://www.youtube.com/watch?v=xweiQukBM_k

25. Ionic compounds form between metals and nonmetals

26. What If No One Will Give Up An Electron? • Covalent Bonds - • 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!

27. Covalent Bonds • 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.

28. Covalent compounds form between 2 nonmetals

29. 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 = NM + M covalent = NM + NM)

30. 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

31. Dot structures – Bonding

32. How many bonds are formed? • Carbon • Nitrogen • Oxygen • Hydrogen

33. Make Some Molecules • Ammonia – NH3 • Methane – CH4 • Carbon Dioxide – CO2 • Propane – C3H8 • Urea – H4N2CO • Glucose – C6H12O6

34. Chemical Reactions • When one set of chemicals changes into another set of chemicals, a chemical reaction occurs • Bonds are either broken or formed (or both!)

35. Our bodies use nutrients through chemical reactions! • Reactants – molecules/elements prior to reaction • Products – molecule/elements produced as a result of the reaction C6H12O6 + O2 CO2 + H2O Energy

36. Chemical Equations • Represent a reaction • Give the types and amounts of substances that react and form Reactants Products 2H2 + O2 “yields” “yields” 2H2O

37. Law of conservation of mass • States that matter is not created or destroyed during a chemical reaction • Even though the matter may change from one form to another, the same number of atoms exists before and after the change takes place! Mass of Reactants Mass of Products

38. O2 2 H2 2 H2O Lets Make water!

39. Iron + Oxygen  Ironoxide

40. TAKE A LOOK AT THE NUMBERS Each made of TWO oxygen atoms Fe Fe O2 Fe2O3 Fe2O3 Fe Fe O2 O2 What about the PRODUCT? How many Oxygen molecules? How many Iron molecules? PRODUCT REACTANTS

41. How do we write it? Fe + O2 Fe2O3 N2 + H2 NH3 KClO3 KCl + O2

42. CO2 + H2O  C6H12O6 + O2 C8H18 +   O2 CO2 + H2O NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2

43. Organic Compounds

44. Organic Compounds • Make up living organisms • Contain the element carbon 4 valence electrons = 4 covalent bonds

45. Organic Compounds • The carbon atom is versatile, it can form large, complex compounds called macromolecules • Monomer– • Polymer –

46. Organic Compounds Four main types of organic macromolecules: Carbohydrates Lipids Proteins Nucleic Acids

47. Carbohydrates • Made of C, H, & O • H to O ratio is always 2:1 • Monomer – monosaccharide • Ex. Glucose, sucrose • Polymer – polysaccharide • Ex. Starch, cellulose, fiber • Main energy source for living things

48. Carbohydrates • Monosaccharide • Examples: • glucose – in many plant and animal tissues, most common monosaccharide • fructose – in many fruits • galactose – component of milk

49. Carbohydrates • polysaccharides • Examples: • glycogen – animals use to store excess sugar • plant starch – plants use to store excess sugar • cellulose – fibers that give plants their rigidity & strength

50. Carb Sizes