1402 Chapter 2 • Nitrogen, Carbon, Hydrogen and Oxygen make up 96% of the human body. • Compounds consists of two or more elements in a fixed ratio. Sugar contains carbon, hydrogen, and oxygen in a fixed ratio. • Elements such as iodine, iron, and copper are needed in amounts less than 0.01%. Despite the small amounts, these elements are required for vital functions. Deficiency in iodine, for example, can produce a goiter, a large swelling in the neck. • Electrons are negatively charged particles. In a neutral atom, the number of electrons is equal to the number of protons. When an atom loses or gains electrons, its charge becomes positive or negative, respectively. • Covalent bonds, which involve sharing electrons, are the strongest bonds. All the other bond types are a form of ionic interaction. Ionic bonds are the second strongest and hydrogen bonds are the weakest. • As heat is absorbed by the water molecules, the hydrogen bonds break. These molecules that have the greatest energy leave as sweat evaporates from your skin. The surface of the liquid
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