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  1. 2 Chemistry Comes Alive: Part A

  2. Matter • Anything that has mass and occupies space • States of matter: • Solid—definite shape and volume • Liquid—definite volume, changeable shape • Gas—changeable shape and volume

  3. Energy • Capacity to do work or put matter into motion • Types of energy: • Kinetic—energy in action • Potential—stored (inactive) energy PLAY Animation: Energy Concepts

  4. Forms of Energy • Chemical energy—stored in bonds of chemical substances • Electrical energy—results from movement of charged particles • Mechanical energy—directly involved in moving matter • Radiant or electromagnetic energy—exhibits wavelike properties (i.e., visible light, ultraviolet light, and X-rays)

  5. Energy Form Conversions • Energy may be converted from one form to another • Conversion is inefficient because some energy is “lost” as heat

  6. Composition of Matter • Elements • Cannot be broken down by ordinary chemical means • Each has unique properties: • Physical properties • Are detectable with our senses, or are measurable • Chemical properties • How atoms interact (bond) with one another

  7. Composition of Matter • Atoms • Unique building blocks for each element • Atomic symbol: one- or two-letter chemical shorthand for each element

  8. Major Elements of the Human Body • Oxygen (O) • Carbon (C) • Hydrogen (H) • Nitrogen (N) About 96% of body mass

  9. Lesser Elements of the Human Body • About 3.9% of body mass: • Calcium (Ca), phosphorus (P), potassium (K), sulfur (S), sodium (Na), chlorine (Cl), magnesium (Mg), iodine (I), and iron (Fe)

  10. Trace Elements of the Human Body • < 0.01% of body mass: • Part of enzymes, e.g., chromium (Cr), manganese (Mn), and zinc (Zn)

  11. Atomic Structure • Determined by numbers of subatomic particles • Nucleus consists of neutrons and protons

  12. Atomic Structure • Neutrons • No charge • Mass = 1 atomic mass unit (amu) • Protons • Positive charge • Mass = 1 amu

  13. Atomic Structure • Electrons • Orbit nucleus • Equal in number to protons in atom • Negative charge • 1/2000 the mass of a proton (0 amu)

  14. Models of the Atom • Orbital model: current model used by chemists • Depicts probable regions of greatest electron density (an electron cloud) • Useful for predicting chemical behavior of atoms

  15. Models of the Atom • Planetary model—oversimplified, outdated model • Incorrectly depicts fixed circular electron paths • Useful for illustrations (as in the text)

  16. Nucleus Nucleus Helium atom Helium atom 2 protons (p+) 2 neutrons (n0) 2 electrons (e–) 2 protons (p+) 2 neutrons (n0) 2 electrons (e–) (a) Planetary model (b) Orbital model Proton Neutron Electron Electron cloud Figure 2.1

  17. Identifying Elements • Atoms of different elements contain different numbers of subatomic particles • Compare hydrogen, helium and lithium (next slide)

  18. Proton Neutron Electron Hydrogen (H) (1p+; 0n0; 1e–) Helium (He) (2p+; 2n0; 2e–) Lithium (Li) (3p+; 4n0; 3e–) Figure 2.2

  19. Identifying Elements • Atomic number = number of protons in nucleus

  20. Identifying Elements • Mass number = mass of the protons and neutrons • Mass numbers of atoms of an element are not all identical • Isotopes are structural variations of elements that differ in the number of neutrons they contain

  21. Identifying Elements • Atomic weight = average of mass numbers of all isotopes

  22. Proton Neutron Electron Hydrogen (1H) (1p+; 0n0; 1e–) Deuterium (2H) (1p+; 1n0; 1e–) Tritium (3H) (1p+; 2n0; 1e–) Figure 2.3

  23. Radioisotopes • Spontaneous decay (radioactivity) • Similar chemistry to stable isotopes • Can be detected with scanners

  24. Radioisotopes • Valuable tools for biological research and medicine • Cause damage to living tissue: • Useful against localized cancers • Radon from uranium decay causes lung cancer

  25. Molecules and Compounds • Most atoms combine chemically with other atoms to form molecules and compounds • Molecule—two or more atoms bonded together (e.g., H2 or C6H12O6) • Compound—two or more different kinds of atoms bonded together (e.g., C6H12O6)

  26. Mixtures • Most matter exists as mixtures • Two or more components physically intermixed • Three types of mixtures • Solutions • Colloids • Suspensions

  27. Solutions • Homogeneous mixtures • Usually transparent, e.g., atmospheric air or seawater • Solvent • Present in greatest amount, usually a liquid • Solute(s) • Present in smaller amounts

  28. Concentration of Solutions • Expressed as • Percent, or parts per 100 parts • Milligrams per deciliter (mg/dl) • Molarity, or moles per liter (M) • 1 mole = the atomic weight of an element or molecular weight (sum of atomic weights) of a compound in grams • 1 mole of any substance contains 6.02  1023 molecules (Avogadro’s number)

  29. Colloids and Suspensions • Colloids (emulsions) • Heterogeneous translucent mixtures, e.g., cytosol • Large solute particles that do not settle out • Undergo sol-gel transformations • Suspensions: • Heterogeneous mixtures, e.g., blood • Large visible solutes tend to settle out

  30. Solution Colloid Suspension Solute particles are very tiny, do not settle out or scatter light. Solute particles are larger than in a solution and scatter light; do not settle out. Solute particles are very large, settle out, and may scatter light. Solute particles Solute particles Solute particles Example Mineral water Example Gelatin Example Blood Figure 2.4

  31. Mixtures vs. Compounds • Mixtures • No chemical bonding between components • Can be separated physically, such as by straining or filtering • Heterogeneous or homogeneous • Compounds • Can be separated only by breaking bonds • All are homogeneous

  32. Chemical Bonds • Electrons occupy up to seven electron shells (energy levels) around nucleus • Octet rule: Except for the first shell which is full with two electrons, atoms interact in a manner to have eight electrons in their outermost energy level (valence shell)

  33. Chemically Inert Elements • Stable and unreactive • Outermost energy level fully occupied or contains eight electrons

  34. (a) Chemically inert elements Outermost energy level (valence shell) complete 8e 2e 2e Helium (He) (2p+; 2n0; 2e–) Neon (Ne) (10p+; 10n0; 10e–) Figure 2.5a

  35. Chemically Reactive Elements • Outermost energy level not fully occupied by electrons • Tend to gain, lose, or share electrons (form bonds) with other atoms to achieve stability

  36. (b) Chemically reactive elements Outermost energy level (valence shell) incomplete 4e 2e 1e Hydrogen (H) (1p+; 0n0; 1e–) Carbon (C) (6p+; 6n0; 6e–) 1e 6e 8e 2e 2e Oxygen (O) (8p+; 8n0; 8e–) Sodium (Na) (11p+; 12n0; 11e–) Figure 2.5b

  37. Types of Chemical Bonds • Ionic • Covalent • Hydrogen

  38. Ionic Bonds • Ions are formed by transfer of valence shell electrons between atoms • Anions (– charge) have gained one or more electrons • Cations (+ charge) have lost one or more electrons • Attraction of opposite charges results in an ionic bond

  39. + – Sodium atom (Na) (11p+; 12n0; 11e–) Chlorine atom (Cl) (17p+; 18n0; 17e–) Sodium ion (Na+) Chloride ion (Cl–) Sodium chloride (NaCl) (a) Sodium gains stability by losing one electron, and chlorine becomes stable by gaining one electron. (b) After electron transfer, the oppositely charged ions formed attract each other. Figure 2.6a-b

  40. Formation of an Ionic Bond • Ionic compounds form crystals instead of individual molecules • NaCl (sodium chloride)

  41. CI– Na+ (c) Large numbers of Na+ and Cl– ions associate to form salt (NaCl) crystals. Figure 2.6c

  42. Covalent Bonds • Formed by sharing of two or more valence shell electrons • Allows each atom to fill its valence shell at least part of the time

  43. Reacting atoms Resulting molecules + or Structural formula shows single bonds. Molecule of methane gas (CH4) Hydrogen atoms Carbon atom (a) Formation of four single covalent bonds: carbon shares four electron pairs with four hydrogen atoms. Figure 2.7a

  44. Reacting atoms Resulting molecules + or Structural formula shows double bond. Molecule of oxygen gas (O2) Oxygen atom Oxygen atom (b) Formation of a double covalent bond: Two oxygen atoms share two electron pairs. Figure 2.7b

  45. Reacting atoms Resulting molecules + or Structural formula shows triple bond. Molecule of nitrogen gas (N2) Nitrogen atom Nitrogen atom (c) Formation of a triple covalent bond: Two nitrogen atoms share three electron pairs. Figure 2.7c

  46. Covalent Bonds • Sharing of electrons may be equal or unequal • Equal sharing produces electrically balanced nonpolar molecules • CO2

  47. Figure 2.8a

  48. Covalent Bonds • Unequal sharing by atoms with different electron-attracting abilities produces polar molecules • H2O • Atoms with six or seven valence shell electrons are electronegative, e.g., oxygen • Atoms with one or two valence shell electrons are electropositive, e.g., sodium

  49. Figure 2.8b

  50. Figure 2.9