Chapter 2

Chapter 2 - Chapter 2: Matter and Energy Chemical Elements...

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Chapter 2: Matter and Energy Chemical Elements and Atomic Structure. Matter and the Elements. Matter has a mass and occupies space. The simplest form of matter is an element. Each element can be identified by its atomic number, the number of protons in its nucleus. There are 91 naturally occurring elements, six of which ( O,C,H,N,Ca, and P) account for 98.5% of the weight of the body. Another 6 elements ( S,K,Na,Cl,Mg and Fe) make up the next 0.8% of body weight. Trace elements 9 Cr, Co, Cu, F, I, and Mn) play vital roles in physiology even though they make up only 0.7% of body weight. The abundance of elements within the body is different from the relative quantities that occur in nature. The body is selective in its use of elements. Atomic Structure All matter is composed of atoms. Atoms are made up of positively charged protons and neutral neutrons occupying the nucleus and tiny, negatively charged electrons in orbit around the nucleus. Each proton or neutron weighs one atomic mass unit. Atomic mass equals the number of protons plus the number of neutrons for an element. Electrons determine the chemical properties on the atom. When the number of protons and number of neutrons are equal, the atom is electrically neutral. Electrons encircle the nucleus in electron shells or energy levels. The innermost shell can hold up to two electrons. The outermost shell, holding the valence electrons can have eight electrons following the octet rule of eights. Isotopes and Atomic Weight. Isotopes vary in their number of neutrons. All isotopes of the same element behave the same chemically. Atomic weight considers the average mass of the atoms in a sample of an element. Ions. Ions are charged particles ( not electrically neutral). Formation of ions is called ionization. An anion has gained an electron and thus carries a negative charge. A cation has lost an electron and bears a positive charge. The charge of an ion is its valence. Electrolytes Electrolytes are molecules that ionize in water, forming a solution than can conduct electricity. Electrolytes are essential to nerve and muscle function. Free Radicals
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Chapter 2 - Chapter 2: Matter and Energy Chemical Elements...

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