Outline The Nature of Molecules 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 Atomic Structure All matter is composed of atoms. Understanding the structure of atoms is critical to understanding the nature of biological molecules. Atomic Structure Atoms are composed of -protons positively charged particles -neutrons neutral particles -electrons negatively charged particles 1
Structure of an Atom Atomic Number & Mass Number + + Helium atom 2e + + Electron cloud Nucleus 2 + Protons Atomic number = 2 2 Neutrons Mass number = 4 2 Electrons Periodic Table of the Elements Atomic Structure Neutral atoms have the same number of protons and electrons. Ions are charged atoms. -cations have more protons than electrons and are positively charged -anions have more electrons than protons and are negatively charged 2
Isotopes of Carbon Chart of Isotopes Radioactive Decay Radioactivity neutron proton Beta neutron decay to loss of electron + electron Alpha loss of two neutrons and two protons Gamma loss of energy Carbon 14 Nitrogen 14 3
Radioactive isotope half life Radioactive Dating C-14 5600 years H-3 12.25 years U-238 4.5 billion years Radioactive isotope half life C-14 5730 years H-3 12.25 years U-238 4.5 billion years Energy from different sources Source Firewood Coal Natural Gas Crude oil Uranium (nuclear fission) Energy (MJ/kg) 16 9-30 39 45 500,000 Summary of Isotopes 90 naturally occurring elements 270 stable isotopes 50 natural radioisotopes 1000 s artificial isotopes Radioactivity Nuclear in origin Releases energy (alpha, beta, gamma) Uses: Energy, Dating Materials, Research & Medicine 4
Atomic Structure 1. Electrons travel in orbitals Elements Octet rule: Atoms tend to establish completely-full outer energy levels. 2. Electrons have energy levels 2 8 8 Outermost energy level Electrons increase in # Periodic Table Groups & Valence Electrons Energy Levels Increase Electron Energy Levels Valence electrons are the electrons in the outermost energy level of an atom. An element s chemical properties depend on interactions between valence electrons of different atoms. Group 1 2 3 4 5 6 7 8 Outer Energy Electrons 1 2 3 4 5 6 7 8 5
Chemical Bonds Molecules are groups of atoms held together in a stable association. Chemical Bonds Ionic bonds are formed by the attraction of oppositely charged ions. Compounds are molecules containing more than one type of element. Atoms are held together in molecules or compounds by chemical bonds. Chemical Bonds Molecules Have Emergent Properties Sodium Chlorine Sodium Chloride Chemical Bonds Covalent bonds form when atoms share 2 or more valence electrons. Covalent bond strength depends on the number of electron pairs shared by the atoms. single bond double bond < < triple bond 6
Chemical Bonds Water Structure and Hydrogen Bonding Water Structure and Hydrogen Bonding Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Properties of Water Fig. 2.15(TE Art) Hydrogen bond ( ) (+) H Cohesion Adhesion (+) ( ) (+) ( ) O H (+ ) ( ) 7
High Surface Tension Properties of Water Properties of Water 2260 kj.kg -1 Heat of vaporization Specific Heat Air 1.0 J g -1 Water 4.2 J g-1 High Specific Heat High Heat of Vaporization Properties of Water Fig. 2.11b Ice Formation Water Ice Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Properties Fig. 2.17(TE of Water Art) Cl Cl Na + Na + Cl Na + Na + Cl Solvent forms Hydration Shells Salt crystal Water molecules 8
Properties of Water - Summary Acids and Bases 1. Hydrogen bonding between water molecules 2. Cohesion, adhesion & surface tension 3. Specific heat High 4. Heat of vaporization High 5. Ice less dense than liquid water 6. Solvent great with polar/charged molecules Acids and Bases Most biological buffers consist of a pair of molecules, one an acid and one a base. Acids and Bases Acid: a chemical that releases H +1 ions. Base: a chemical that accepts H +1 ions. Buffer: a chemical that accepts/releases H +1 as necessary to keep ph constant 35 36 9
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