2 inorganic 118 - Biology 118 2. ATOMS, BONDS, AND WATER...

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Biology 118 2. ATOMS, BONDS, AND WATER WHAT ARE YOU MADE OF? Life’s made up of 25 naturally occurring elements. The top 13 are shown in Table 2-1, and the rest are considered trace elements (copper, for example). The prevalence of the top 4 elements (O, C, H, N – about 96% of human body weight) is due in part to their availablity and abundance in the Earth’s crust. The top 4 can also form strong covalent bonds -- meaning reasonable stability of resulting molecules. ATOMS ARE FUN! Basic parts of atom: protons, neutrons, electrons. Protons and neutrons cluster in a nucleus, while electrons orbit in a cloud. Atoms are neutral when the number of protons (positively charged) match the number of electrons (negatively charged). Electrons orbit the nucleus in ordered ‘shells’, which can hold only so many electrons; the first shell holds 2, the second holds 8. Look at neon: 10 protons in the nucleus, 10 orbiting electrons (2 in first shell, 8 in second shell). But what happens if an outer shell isn’t completely filled? Look at carbon: 6 protons, 6 electrons, so that means only 4 in the outer shell. What to do? Carbon is reactive, it interacts with other atoms, in an attempt to fill those 4 empty spaces in the outer shell. How to do that? BONDING
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This note was uploaded on 11/02/2011 for the course BIO 118 taught by Professor Bilgen during the Winter '08 term at University of Washington.

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2 inorganic 118 - Biology 118 2. ATOMS, BONDS, AND WATER...

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