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BChem - Biological Chemistry The universe is composed of...

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Biological Chemistry Heyer 1 Life, Life, the Universe, the Universe, and Everything and Everything E=mc 2 The universe is composed of energy and matter . At the beginning of the universe, energy was converted into matter. Big Bang! Only in rare circumstances, like inside stars and atomic blasts, matter is converted back into energy. •Energy is often converted from one form into another: (e.g., light energy into chemical energy; chemical enegy into kinetic energy; kinetic energy into heat energy; etc.) but it is neither created nor destroyed. •But matter, with rare exceptions, stays the same type of matter. Matter is in the form of chemicals. Chemicals are constructed from atoms. Different types of matter, i.e., different elements, have different atoms. The Atom A single unit of matter Composed of three types of subatomic particles – Neutrons (n o ): mass = 1 atomic mass unit no electrical charge (neutral) – Protons (p + ): mass = 1 atomic mass unit positive electrical charge (+1) – Electrons (e ): mass is trivial negative electrical charge (–1) Atomic Structure [p+] [n°] [e-] Neutrons and protons form the nucleus Atomic Mass (Atomic Weight) = number of protons and neutrons combined Electrons orbit around the nucleus Atomic Number A chemical reaction is the interaction of electrons from different atoms. The number, distribution and activity of electrons around an atom’s nucleus is determined by the number of protons in that nucleus. The “chemical identity” (type of element) for any atom is determined by the number of protons in its nucleus! # of p + = the Atomic Number for that atom. E.g.: Any atom that has 6 p + in its nucleus (atomic number = 6) is defined as carbon , no matter how many e - or n° it has! .. Partial Periodic Table atomic number
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Biological Chemistry Heyer 2 96% of body mass is composed of four different elements O xygen (65%) C arbon (18%) H ydrogen (10%) N itrogen (3%) Remember: 65-75% of total body weight is H 2 0 Table 2.1 Atoms of the same element (i.e., same atomic number) but with differing numbers of neutrons, have the same chemical identity but different atomic weights. These variations of an element are called isotope s. Some isotopes are unstable and emit radioactive energy. Such isotopes are radioisotopes . Isotopes Electron shell Electrons have different levels of energy Each energy level is called an electron shell Outer shell called valence shell Only valence shell electrons participate in chemical reactions Ions If # p + = # e : neutral atom If # p + # e : charged atom = ion If the valence shell loses an electron = positive ion ( cation ). If the valence shell gains an electron = negative ion ( anion ). Ions & Isotopes Chemical reactions occur when bonds between atoms are formed or rearranged Molecule: two or more atoms bonded together – Compound: molecule constructed of more than one kind of atom.
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