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TORTORA • FUNKE • CASE Microbiology AN INTRODUCTION EIGHTH EDITION B.E Pruitt & Jane J. Stein Chapter 2, part A Chemical Principles Chemistry • Chemistry is the study of interactions between atoms and molecules. • The atom is the smallest unit of matter that enters into chemical reactions. • Atoms interact to form molecules. The Study of Atoms Atoms are composed of • Electrons: negatively charged particles, no weight • Protons: positively charged particles, 1 amu • Neutrons: uncharged particles, 1 amu • Amu = atomic mass unit 6 X 1023 = 1 gram Atomic weight is the weight of the atom - the sum of it’s parts: protons and neutrons Atomic number is the number of protons. The Study of Atoms • Protons and neutrons are in the nucleus. • Electrons move around the nucleus. Figure 2.1 Chemical Elements • Each chemical element has a different number of protons - it’s atomic number. • Isotopes of an element are atoms with different numbers of neutrons than typical for that atom. Carbon 14 versus 12. Isotopes of oxygen are: 16 8 O 17 8 O 18 8 O Table 2.1 Electronic Configurations • Electrons are arranged in electron shells corresponding to different energy levels. Electronic Configurations Table 2.2.1 Electronic Configurations Table 2.2.2 How Atoms Form Molecules: Chemical Bonds • Atoms combine to complete the outermost shell. • The number of electrons in this shell is the valence. How Atoms Form Molecules: Chemical Bonds • A compound contains different kinds of atoms. H2O • The forces holding atoms in a compound are chemical bonds. Types of bonds: • Ionic - exchange of electronics making ions • Covalent - shared electrons • Polar unequal sharing • Hydrogen bonds - between molecules How Atoms Form Molecules: Chemical Bonds • The number of protons and electrons is equal in a neutral atom. • Ions are atoms that have gained or lost electrons and are charged. Figure 2.2a Ionic Bonds • Ionic bonds are attractions between ions of opposite charge. One atom loses electrons and another gains electrons. Figure 2.2b Covalent Bonds • Covalent bonds form when two atoms share one or more pairs of electrons. Figure 2.3a Hydrogen Bonds • Hydrogen bonds form when a hydrogen atom covalently bonded to an O or N atom in another molecule. Figure 2.4 Molecular Weight and Moles • The sum of the atomic weights in a molecule is the molecular weight. • One mole of a substance is its molecular weight in grams. H2O 2H =21 =2 O = 16 MW = 18 1 mole weighs 18 g Chemical Reactions • Chemical reactions involve the making or breaking of bonds between atoms. • A change in chemical energy occurs during a chemical reaction. • Endergonic reactions absorb energy. • Exergonic reactions release energy. Synthesis Reactions • Occur when atoms, ions, or molecules combine to form new, larger molecules A Atom, ion, or molecule A + B Atom, ion, or molecule B AB New molecule AB • Anabolism is the synthesis of molecules in a cell. Decomposition Reactions • Occur when a molecule is split into smaller molecules, ions, or atoms. Breaks down into AB New molecule AB A Atom, ion, or molecule A + B Atom, ion, or molecule B • Catabolism is the decomposition reactions in a cell. Exchange Reactions • Are part synthesis and part decomposition. NaOH + HCl NaCl + H2O Reversible Reactions • Can readily go in either direction. • Each direction may need special conditions. Heat A + B AB Water