Ch 2-Atoms&Molecules

Ch 2-Atoms&Molecules - Ch2 - ATOMS AND MOLECULES...

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Ch2 - ATOMS AND MOLECULES All organisms have very similar chemistry - same physical and chemical laws: organic - generally large, complex substances that contain a "backbone" of carbon molecules inorganic - simple substances - the basics Elements cannot be broken down by chemical reaction - represented by symbols, usually first letter of the name Many - 92 naturally occurring elements Few - 20 compose living organisms 4 make up most of the mass of most organisms [ OCHN ] Others (calcium, phosphorus, potassium, magnesium) are consistently present trace elements - are present in minute amounts Atom - smallest unit of an element - retains chemical properties of the element made up of subatomic particles - 3 important here: Protons with + charge in nucleus Neutrons with no charge in nucleus Electrons with - charge determine the character of the atom - how it reacts same in number as protons - in neutral atom fly around in vast space surrounding nucleus - fly off in straight line but attracted by + protons in the nucleus repel each other because have same charge orbit in clouds - the 2 e in any orbital are more likely found in this 3-dimensional space - exist in E shells/levels ( E it takes to move e that far from nucleus) - the # of e in a shell depends on how many orbitals it has Bohr model - uses circles for the E levels - orbital shapes are not shown shell level orbitals # of e to fill K 1 1 2 e L 2 4 8 e M 3 9 18 e (stable with 8) If an atom absorbs a quantum of E (heat, electricity, light) e can temporarily jump into a higher E level - excited state Atomic number = number of protons - unique for each element, dictates number of electrons also (+ and - balance) written as a subscript - 8 O oxygen - 8 protons therefore 8 electrons Atomic mass = protons + neutrons - written as a superscript - 16 O oxygen has 16 protons and neutrons (therefore 8 neutrons) - an electron's mass is nearly negligible (so tiny) so it is not considered in the atomic mass Isotopes are atoms of the same element with different numbers of neutrons (different mass) Carbon exists as 3 isotopes, all have 6 protons but different # neutrons: 12 C 6 neutrons - 99% of all C 13 C 7 neutrons - next common 14 C 8 neutrons -least common - radioactive Generally act same except some are unstable and breakdown releasing E - these are radioactive isotopes such as 3 H, 32 P, 14 C - valuable in research since they behave very much like other atoms of that element except for the E they give off which can be used as a label to follow their activity - radioactive decay rate is always constant and expressed as -half-life -the time it takes for 50% to decay - 14 C has a half-life of 5600 yrs so 1 g today would contain .5 g in 5600 yr. etc. - estimate age by comparing ratio of isotopes left with expected amount Molecule - composed of more than one atom held together by chemical bonds H 2 , O 2 are molecules of elements H 2 O, C 6 H 12 O 6 , CO 2 are molecules of compounds Compounds - composed of more than one
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This note was uploaded on 02/07/2011 for the course BIO 1110 taught by Professor Mcdearman during the Spring '11 term at UT Chattanooga.

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Ch 2-Atoms&Molecules - Ch2 - ATOMS AND MOLECULES...

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