Anatomy & Physiology I and II

Anatomy & Physiology Study Guide

©2018 Achieve Test Prep Page 50 of 367 Solutions are homogenous mixtures of different components. It is comprised of a solvent (usually a liquid) that is present in great amounts and solutes (usually solid) that are present in smaller amounts. Mixtures have physically mixed components that do not involve chemical bonding and can be separated by physical means. Suspension are heterogenous mixtures that have solutes that are visible and observed to settle out from their suspension. Colloids are heterogenous mixtures whose solutes do not settle. 5.2 Chemical Bonding Unstable atoms achieve stability by gaining, losing, or sharing electrons to fill their outermost energy level. The interactions often involve the formation of chemical bonds that connect the participating atoms. There are three basic types of chemical bonds: ionic bonds, covalent bonds, and hydrogen bonds. Chemical bonding creates molecules and compounds. The term molecule refers to any chemical structure consisting of atoms held together by covalent bonds. A compound is a pure chemical substance made up of atoms of two or more different elements joined by any type of bond. Ionic Bonds Ions are atoms or molecules that carry an electric charge, either positive or negative. Cations carry a positive charge (+); ions with a negative charge (−) are called anions . Ionic bonds are chemical bonds created by the electrical attraction between anions and cations. Ions have an unequal number of protons and electrons. When an atom loses or gains electrons, it becomes an ion. In the formation of an ionic bond: • One atom—the electron donor—loses one or more electrons and becomes a cation, with a positive (+) charge Electrons and Energy Levels Atoms are electrically neutral. Every positively charged proton is balanced by a negatively charged electron. Thus, each increase in the atomic number is accompanied by a comparable increase in the number of electrons traveling around the nucleus. Within the electron cloud, electrons occupy an orderly series of energy levels. The first electron shell (the one closest to the nucleus) corresponds to the lowest energy level. Each energy level holds a specific number of electrons. The first energy level can hold at most two electrons, and the next two levels can each hold up to eight electrons. The first energy level must be filled before any electrons enter the second, and the second energy level has to be filled before electrons enter the third level and so on. The outermost energy level is called the valence shell. Atoms with unfilled energy levels are unstable and will react with other atoms in ways that give them full outer electron shells. The atoms that are most important to biological systems are unstable because those atoms interact to form larger structures. Solutions and Mixtures