Microbiology B.E Pruitt & Jane J. Stein AN INTRODUCTION EIGHTH EDITION TORTORA FUNKE CASE 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.

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 = 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. The Study of Atoms Figure 2.1

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: Chemical Elements 16 8 O 17 8 O 18 8 O

Table 2.1

Electrons are arranged in electron shells corresponding to different energy levels. Electronic Configurations

Table 2.2.1

Electronic Configurations Table 2.2.2

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. H 2 O 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. How Atoms Form Molecules: Chemical Bonds Figure 2.2a

Ionic bonds are attractions between ions of opposite charge. One atom loses electrons and another gains electrons. Ionic Bonds Figure 2.2b

Covalent bonds form when two atoms share one or more pairs of electrons. Covalent Bonds Figure 2.3a

Hydrogen bonds form when a hydrogen atom covalently bonded to an O or N atom in another molecule. Hydrogen Bonds Figure 2.4

The sum of the atomic weights in a molecule is the molecular weight. One mole of a substance is its molecular weight in grams. Molecular Weight and Moles H 2 O 2H = 2  1 = 2 O = 16 MW= 18 1 mole weighs 18 g

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. Chemical Reactions

Occur when atoms, ions, or molecules combine to form new, larger molecules Anabolism is the synthesis of molecules in a cell. Synthesis Reactions A+BAB Atom, ion, or molecule A  Atom, ion, or molecule B New molecule AB

Occur when a molecule is split into smaller molecules, ions, or atoms. Catabolism is the decomposition reactions in a cell. Decomposition Reactions A+B AB Atom, ion, or molecule A  Atom, ion, or molecule B New molecule AB Breaks down into

Are part synthesis and part decomposition. Exchange Reactions NaCl+H2OH2O  NaOH+HCl

Can readily go in either direction. Each direction may need special conditions. Reversible Reactions A+B Water  AB Heat