Nitrogen 3 remember 65 75 of total body weight is h20

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Unformatted text preview: ve the same chemical identity but different atomic weights. • Nitrogen (3%) Remember: 65-75% of total body weight is H20 Electron shell • These variations of an element are called isotopes. • Some isotopes are unstable and emit radioactive energy. Such isotopes are radioisotopes. Ions • Electrons have different levels of energy • Each energy level is called an electron shell • Outer shell called valence shell • If # p+ = # e–: neutral atom • Only valence shell electrons participate in chemical reactions • If the valence shell loses an electron = positive ion (cation). Ions & Isotopes • If # p+ ≠ # e–: charged atom = ion • If the valence shell gains an electron = negative ion (anion). Chemical reactions occur when bonds between atoms are formed or rearranged + 2 H2 + Reactants O2 2 H2O Reaction Products • Molecule: two or more atoms bonded together – Compound: molecule constructed of more than one kind of atom. E.g.: H2 and O2 and H2O are all molecules. • But H2 and O2 are elemental molecules. • And H2O is a compound molecule. Heyer 2 Biological Chemistry Molecules can be represented in many ways Electronshell diagram Name (molecular formula) (a) Hydrogen (H 2 ). Two hydrogen atoms can form a single bond. (b) H O Water (H 2O). H O O H Ball-and-stick model Hybrid-orbital model (with ball-and-stick model superimposed) •Biological molecules have many atoms bound precisely in complex forms. •How does the right rearrangement of the right bond at the right time happen? H O H H Methane (CH 4 ). Four hydrogen atoms can satisfy the valence of one carbon atom, forming methane. O O Two hydrogen atoms and one oxygen atom are joined by covalent bonds to produce a molecule of water. (d) H Spacefilling model Oxygen (O 2). Two oxygen atoms share two pairs of electrons to form a double bond. (c) Structural formula Living cells carry out millions of chemical reactions that rearrange matter in significant ways C H C 104.5 ° H H H H H H C H H H H H H H O O H H H H Unbonded Electron pair C H H...
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