d. Using Figure 4.1 as a guide, draw a shell model of these molecules: Potassium Chloride (KCI) on DOS Calcium Chloride (CaCl) 900 level consists of com- plex chemical reactions. Therefore, it is important to have a basic understanding of chemical reactions and the chemicals composing biological organisms. Chemical substances are classified into two groups: elements and compounds. An element is a substance that cannot be broken down by chemical means into any simpler substance. Table 4.1 lists the most com- mon elements found in living organisms. An atom TABLE 4.1 Element Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Potassium Sulfur Sodium Chlorine Magnesium Iron lodine *By weight. COMMON ELEMENTS IN THE HUMAN BODY Symbol OUIZax 2022_ Percentage* 65 SBONIO 18 10 2 is the smalle perties (chan Two or and1 compound. simple cor are comple pound tha molecule. chemical 0.35 0.25 0.15 0.15 0.05 0.004 0.0004 ATOM Atoms proton trons H the cer sess a have charg spee tion keer F oth tor de ha ta trigia