微生物學-02-化學原理.ppt

Chapter 2 Chemical Principles QA A Salmonella bacterium releases a regulatory molecule containing amino acids and phosphate that causes a human cell’s cytoskeleton to change shape, thereby allowing the bacterium to enter the cell. What type of chemical is this regulatory molecule? The Structure of Atoms 2-1 Describe the structure of an atom and its relation to the physical properties of elements. 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 Structure of Atoms Atoms are composed of Electrons：Negatively charged particles Protons：Positively charged particles Neutrons：Uncharged particles Protons and neutrons are in the nucleus Electrons move around the nucleus Each chemical element has a different number of protons Isotopes of an element are atoms with different numbers of neutrons. Chemical Elements Electronic Configurations Electrons are arranged in electron shells corresponding to different energy levels Electronic Configurations How Atoms Form Molecules 2-2 Define ionic bond, covalent bond, hydrogen bond, molecular weight, and mole. Atoms combine to complete the outermost shell The number of missing or extra electrons in this shell is known as the valence Molecules hold together because the valence electrons of the combining atoms form attractive forces, called chemical bonds, between the atomic nuclei. Chemical Bonds A compound contains different kinds of atoms. ex. H2O Ionic Bonds Ionic Bonds Ionic bonds are attractions between ions of opposite charge. One atom loses electrons, and another gains electrons. Covalent Bonds Covalent bonds form when two atoms share one or more pairs of electrons Hydrogen Bonds Hydrogen bonds form when a hydrogen atom that is covalently bonded to an O or N atom is attracted to another N or O atom in another molecule. Molecular Weight and Moles The sum of the atomic weights in a molecule is the mol