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Teresa Audesirk • Gerald Audesirk • Bruce E. Byers

Biology: Life on Earth Eighth Edition
Lecture for Chapter 2 Atoms, Molecules, and Life

Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 2 Outline
•  2.1 What Are Atoms? p. 22 •  2.2 How Do Atoms Interact to Form Molecules? p. 23 •  2.3 Why is Water So Important to Life? p. 28

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Section 2.1 Outline•  2.1 What Are Atoms?
–  Atoms Are Basic Structural Units Composed of Still Smaller Particles –  Electrons Orbit the Nucleus at Fixed Distances –  Life Depends on the Ability of Electrons to Capture and Release Energy

Atoms
•  Atoms are the fundamental structural units of matter and are composed of three types of particles •  In the central nucleus there are positively charged protons anduncharged neutrons •  In orbit around the nucleus are negatively charged particles called electrons

Otras Subparticulas atómicas

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Estructura del Átomo

Atoms
•  Atoms are electrically neutral because they have an equal number of positive protons as negative electrons

Átomos
•  El número de protones en el núcleo de un átomo se conoce como número atómico •  La Σ de protones yneutrones es la masa atómica •  Los electrones no se cuentan en el computo de masa atómica

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Elementos e Isótopos
•  En elemento es una substancia que no puede ser degradada por reacciones químicas ordinarias •  Se agrupan en la tabla periódica •  117 elementos; 96 naturales, 21 artificiales

Elementos más comunes en el sistema solar

Elements and Isotopes
•  The atomicnumber (number of protons) is the defining value for an element
–  All atoms of an element have the same atomic number –  e.g. Carbon has 6 protons, nitrogen has 7

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Elements and Isotopes
•  Atoms of an element may vary in the number of neutrons they have in the nucleus
–  Variant atomic forms of an element are called isotopes –  Some isotopes are radioactive and are used inresearch

•  Elements may occur as solids, liquids, or gases at room temperature

Algunos Isótopos
•  •  •  •  •  •  •  •  •  •  •  Radioisótopos Americium-241 (Am-241) Cesio-137 (Cs-137) Cobalto-60 (Co-60) Iodo-131 (I-131) Iridio-192 (Ir-192) Plutonium Polonio 210 Estroncio-90 (Sr-90) Uranio-235 (U-235) Uranio-238 (U-238)

Isótopo •  C12 •  C13 •  C14

Abundancia 98.89% 1.11% Trazas

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Electron Shells
•  Larger atoms can accommodate more electrons than smaller ones can •  Electrons are distributed about the nucleus of an atom in electron shells
–  The first shell or energy level holds 2 electrons –  The second shell holds up to 8

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Electron Shells
•  Roles of the nucleus and the electrons
–  The nucleus provides stability –  The electronsinteract with other atoms (e.g. form bonds)

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Energy Capture and Release
•  Life depends on electrons capturing and releasing energy
–  Electron shells correspond to energy levels –  Energy exciting an atom causes an electron jump from a lower- to higher-energy shell –  Later, the electron falls back into its original shell, releasing the energy

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Section 2.2 Outline•  2.2 How Do Atoms Interact to Form Molecules?
–  –  –  –  –  –  –  Atoms Interact When There Are Outermost Electron Shell Vacancies Charged Atoms (Ions) Form Ionic Bonds Uncharged Atoms Can Stabilize by Forming Covalent Bonds Most Biological Molecules Feature Covalent Bonds Electron Sharing Determines Covalent Bond Polarity Highly Reactive Free Radicals Can Damage Cells Hydrogen Bonds AreWeak Attractions Within Some Covalently-Bonded Molecules

Atoms Interact
•  Molecules are made of two or more atoms bonded together through electron shell interactions A substance made of atoms of different elements is a compound

• 

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Atoms Interact
•  Reactions between atoms depend upon the configuration of electrons in the outermost electron shell

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