The Nature of Molecules

Outline Describe the basic structure of an atom Recognize the importance of electrons Understand isotopes and radioactivity Describe chemical bonds and why they form Be aware of the properties of water Understand pH and buffers

Matter, Molecules, Elements & Atoms Compounds … Molecules Elements … Atoms

Structure of an Atom

Mass Number Helium atom Mass number = 4 2 Protons 2 Neutrons 2 – – Electron cloud 2e– + + + + Helium atom Nucleus 2 Protons + Mass number = 4 2 Neutrons 2 – Electrons

Mass Number Carbon atom 6 Mass number = 12 6 6 Protons Neutrons Electron cloud 6e– + + Nucleus Carbon atom 6 + Protons Mass number = 12 6 Neutrons 6 – Electrons

Atomic Number and Atomic Weight (Mass Number)

Periodic Table of the Elements

Frequency of Elements in the Earth’s Crust Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Frequency of Elements in the Earth’s Crust 1 8 H O 2 He 3 4 5 6 C 9 7 10 Li Be B F 14 N Ne 11 Si 12 13 15 Na 16 Mg Al 17 18 P S Cl Ar 26 19 20 22 Ca 21 23 24 25 Fe 27 28 29 30 31 32 33 34 35 36 K Sc Ti V Cr Mn Co Ni Cu Zn Ga Ge As Se Br Kr 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 87 88 89 104 105 106 107 108 109 110 Fr Ra Ac 58 59 60 61 62 63 64 65 66 67 68 69 70 71 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Chemical Composition of the Human Body

Isotopes of Carbon

Chart of Isotopes http://atom.kaeri.re.kr/ton/nuc4.html

Radioactive Decay neutron proton + electron Carbon 14 Nitrogen 14

Radioactivity Beta – neutron decay to loss of electron Alpha – loss of two neutrons and two protons Gamma – loss of energy

Radioactive isotope half life C-14 5600 years H-3 12.25 years U-238 4.5 billion years

Radioactive isotope half life Radioactive Dating Radioactive isotope half life C-14 5730 years H-3 12.25 years U-238 4.5 billion years

Energy from different sources Energy (MJ/kg) Firewood 16 Coal 9-30 Natural Gas 39 Crude oil 45 Uranium (nuclear fission) 500,000

Summary of Isotopes 92 naturally occurring elements 270 stable isotopes 50 natural radioisotopes 1000’s artificial isotopes Radioactivity Nuclear in origin Releases energy energy (alpha, beta, gamma) Uses: Energy, Dating Materials, Research & Medicine

Energy Levels or Electron Shells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Energy Levels or Electron Shells – Energy released Energy absorbed – + + M L K + K L M + + Energy level 3 Energy level 2 Energy level 1 + + Energy level 1 Energy level 2 Energy level 3

Energy Levels (Electron Shells)

Energy Levels (Electron Shells) First electron shell holds 2 electrons Electron Outermost electron shell holds 8 electrons Nucleus Hydrogen (H) Atomic number = 1 Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8

Periodic Table Groups & Valence Electrons Outermost energy level Electrons increase in # Periodic Table Groups & Valence Electrons Energy Levels Increase Group 1 2 3 4 5 6 7 8 Outer Energy Electrons 1 2 3 4 5 6 7 8

Ionic Bond Formation

Molecules Have Emergent Properties Sodium Chlorine Sodium Chloride Molecules have emergent properties.

Covalent Bonding

Covalent Bonds Molecular and Structural Formulas

Water Structure and Hydrogen Bonding

Water Structure and Hydrogen Bonding (+) H (–) O

Properties of Water Fig. 2.15(TE Art) Cohesion Adhesion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 2.15(TE Art) Cohesion Adhesion

Properties of Water High Surface Tension

Properties of Water Moderates Temperature High Heat Storage High Heat of Vaporization

Properties of Water Ice Formation Fig. 2.11b Ice Water

Solvent forms Hydration Shells Properties of Water Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 2.17(TE Art) Solvent forms Hydration Shells Cl– Cl– Na+ Na+ Cl– Na+ Na+ Cl– Water molecules Salt crystal

Table 2.1

Hydrogen ion concentration pH Hydrogen ion concentration

Buffers H2O  H+ + OH-

END Basic Chemistry