TAILIEUCHUNG - Lecture Biology - Chapter 2: The chemistry of life

The objectives of this chapter are to the chemistry of life. After studying this chapter you will be able to understand: What are the chemical elements that make up living organisms? How do atoms bond to form molecules? How do atoms change partners in chemical reactions? What properties of water make it so important in biology? | The Chemistry of Life 2 The Chemistry of Life What Are the Chemical Elements That Make Up Living Organisms? How Do Atoms Bond to Form Molecules? How Do Atoms Change Partners in Chemical Reactions? What Properties of Water Make It So Important in Biology? Figure The Helium Atom All matter is composed of atoms What Are the Chemical Elements That Make Up Living Organisms? Atoms have volume and mass. Mass of one proton or one neutron = atomic mass unit (amu) or 1 dalton, or × 10–24 grams. Mass of one electron = 9 × 10–28—usually ignored What Are the Chemical Elements That Make Up Living Organisms? Protons: positive charge +1 Electrons: negative charge –1 Neutrons: zero charge Atoms: # protons = # electrons—electrically neutral What Are the Chemical Elements That Make Up Living Organisms? Element: pure substance containing only one kind of atom Elements are arranged in the periodic table. Figure The Periodic Table (Part 1) Figure The Periodic Table (Part 2) The number of protons identifies an element. Number of protons = atomic number. He from periodic table here What Are the Chemical Elements That Make Up Living Organisms? All elements except hydrogen have one or more neutrons. Mass number = number of protons + number of neutrons. Mass number ≈ mass of atom in daltons. What Are the Chemical Elements That Make Up Living Organisms? Isotopes: forms of an element with different numbers of neutrons, thus different mass numbers Example: 12C has 6 neutrons 13C has 7 neutrons 14C has 8 neutrons Figure Isotopes Have Different Numbers of Neutrons What Are the Chemical Elements That Make Up Living Organisms? Atomic weight: average of mass numbers of isotopes in their normally occurring proportions Atomic weight of carbon = Atomic weight of hydrogen = What Are the Chemical Elements That Make Up Living Organisms? Radioisotopes are unstable, they give off energy in the form of alpha, beta, and gamma .

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