Chapter 2: The Chemical Context of Life

1. Chapter 2:The Chemical Context of Life

2. Matter • Anything that has mass and occupies space. • Smallest particle of an element (still retains elemental properties) Atom

3. Element • Matter made up of only one type of atom. • 92 natural elements. • Each element has a symbol.

4. Compound • Compound - Elements combined in fixed ratios. • A compound has characteristics beyond those of its combined elements.

6. Question? • What elements are necessary for life? • Life requires about 25 chemical elements.

8. Macroelements • Elements needed in large amounts or quantities. • Macro = Large • Examples: C HOPKNS CaFe Mg NaCl

9. Microelements • Elements needed in very small quantities. • Also known as trace elements. • Micro = small • Examples: Cu, Co, Zn, Mo, I, Mn

10. Atomic Subparticles • Protons + charge, 1 Dalton mass • Neutrons no charge, 1 Dalton mass • Electrons - charge, essentially no mass

11. Atomic Model

12. Atomic Number • The number of protons in the nucleus. • Each element has its own atomic number. • If you change the atomic number, you no longer have the same element.

13. Atomic Mass • The number of protons and neutrons in the nucleus. • The atomic mass can change.

14. Isotopes • Atoms of the same element with different atomic mass • Caused by changes in the number of neutrons • Used as “tracers”, used to kill cancer/bacteria cells, used to determine age of fossils/geological formations

15. Types of Isotopes • Radioactive • Where the nucleus decays spontaneously, giving off particles and energy. • Heavy • Has a stable nucleus, but masses more than the standard isotope for the element.

16. Energy • The ability to do work • THINK = ATP • ATP is how living organisms have the ability to do work • They USE ATP!!!

17. Potential Energy • Is the energy that matter stores simply because of its position or location • Electrons have potential energy because of their position relative to the nucleus

19. Electron Energy Levels • Energy levels around the nucleus of an atom • 1st level can have 2 electrons and has the lowest potential energy • Other levels can hold more than 2 electrons and have higher energy levels

20. Electron Orbitals • The three dimensional space where an electron is found 90% of the time. • Different orbitals have different shapes. • Each orbital can hold only 2 electrons.

21. Electron Orbitals

22. Chemical Behavior Of An Atom • Is determined by its electron configuration in the energy levels and orbitals • This determines who is can bond with (if anyone!)

23. Valence Electrons • The electrons in the outermost energy level • Electrons available chemical bonds • Atoms/Elements with same # of valence electrons will react similarly and will have similar characteristics

24. Octet Rule • The most stable condition is to have an outer level of 8 electrons • Exception - 1st level is stable with only 2 electrons • When stable - no chemical reactions will take place • Ex: Ne, He, (Noble gases)

25. Electrons of the first elements

26. Chemical Bonds • Forces that join atoms together to form molecules • Usually caused by sharing or transferring valence electrons

27. Bond Formation Depends On: • The number of valence electrons that must be gained, lost, or shared to reach the stable condition.

28. Chemical Bond Types • Nonpolar Covalent • Polar Covalent • Ionic • Hydrogen • van der Waals forces

29. Electronegativity • The attractiveness of a specific kind of atom towards e- in another atom • Important in covalent bonds • Periodic Table trend: • More electronegativity = stronger pull of e- • He has highest EN • Increases as you go right and up the table

31. Nonpolar Covalent • When electrons are shared equally between atoms • Very strong bond • Important in many molecules found in living things • Ex: carbon to hydrogen, hydrogen to hydrogen, oxygen to oxygen

32. Nonpolar Covalent • Can be single, double, or triple between two atoms • Each nonpolar covalent bond involves a pair of electrons

34. Polar Covalent • When electrons are shared unequally between atoms • Results in “polar” molecules that have charged areas • Use δ symbol • Ex: Water, H to O bonds

36. Ionic Bonds • Formed when electrons are transferred from one atom to another and ions are formed • Ex: NaCl • Why? Two atoms electronegativity are SO different that one atom gains e- completely

37. Two Types of Ions • Cations - have lost electrons (p+ > e-) giving them a positive charge. • Ex: Sodium (Na+) • Anions- have gained electrons (p+ < e-) giving them a negative charge. • Ex: Chlorine (Cl-)

38. Ionic Bonds • Formed when cations (+) and anions (-) attract each other • Weak chemical bond • Why? Environment easily affects strength of this bond • Ex: Salt  Solid in air/gas; Dissolves in liquid

39. Ionic

40. Hydrogen Bonds • When a hydrogen atom bonded to one molecule is attracted to the slightly negative area (often N or O) of another molecule • Very weak individual bond • Can be a “strong” force if there are many H bonds.

41. Hydrogen bonds • Remember: • H bonds occur BETWEEN MOLECULES (not b/t atoms within ONE molecule) • Ex: H bonds hold water molecules together

42. Hydrogen Bonds

43. Van der Waals • Result of e- ability to move at high speeds • Creates “spots” where there are “pools” of + and – charges • Weak chemical “bond” • Ex: gecko’s feet

45. Molecular Shape • Each molecule on Earth has a characteristic shape • Determined by the positions of the atom’s orbitals • Shape related to function

46. Molecular Shape • Molecular shape is crucial because it determines how most molecules of life recognize and respond to one another. • Ex: • Viruses (reproduction), bacteria (reproduction), hormones/cell recognition

48. Chemical Reactions • The making and breaking of chemical bonds • Reactions do not destroy matter, they only rearrange it

49. Chemical Equations • A way to represent what is happening in a chemical reaction Ex: 2 H2+ O2 2 H2O

50. Parts of the Equation • Reactants: - the starting materials • Products: - the ending materials • Note - all atoms of the reactants must be accounted for in the products 2 H2+ O2 2 H2O