Chapter 2 The Chemical Foundation of Life 1 Be able to Draw a diagram of an atom and label the parts Explain how the structure of atoms changes as you move through the periodic table Explain how isotopes differ from each other and how they can be used in biology Describe the relationship between electronegativity and chemical bonds Compare and contrast covalent and ionic bonds Compare and contrast polar and nonpolar covalent bonds Explain the importance of weak bonds interactions for biology Predict the outcome of altering components of a reaction that was in chemical equilibrium 2 The Building Blocks In this model of an organic molecule the atoms of carbon black hydrogen white nitrogen blue oxygen red and phosphorus yellow are shown in proportional atomic size The silver rods indicate chemical bonds credit modification of work by Christian Guthier 3 Elements and Compounds Organisms are composed of anything that takes up space and has mass Matter is made up of cannot be broken down to other substances by chemical reactions 98 naturally occurring elements 118 total each element has a unique symbol Sulfur S Calcium Ca Sodium Na Elements and the Living World Four most common elements of living organisms Carbon C Oxygen O Hydrogen H Nitrogen N Learn these symbols Trace elements are required in only minute quantities An element s properties depend on the structure of its atoms Each element Consists of a certain kind of atom that is different from those of other elements An atom of an element Is the smallest unit of matter that still retains the properties Atoms 2 main regions Nucleus Orbital cloud Elements such as helium depicted here are made up of atoms Atoms are made up of protons and neutrons located within the nucleus with electrons in orbitals surrounding the nucleus Subatomic Particles Atoms of each element composed of even smaller parts called subatomic particles Relevant subatomic particles include Neutrons which have no electrical charge Protons which are positively charged Electrons which are negatively charged Atomic Number and Atomic Mass Atoms of the various elements differ in of subatomic particles The atomic number of an element is the number of protons is unique to each element Ex carbon and only carbon contains 6 protons The mass number Atomic Mass of an element is the sum of protons plus neutrons in the nucleus of an atom each has a mass close to 1 Dalton atomic mass unit AMU is an approximation of the atomic mass of an atom mass of electrons is 1 1 800th of a dalton so is negligible Atomic mass vs atomic number Carbon has an atomic number of six and two stable isotopes with mass numbers of twelve and thirteen respectively Isotopes Isotopes of a given element differ in the number of neutrons in the atomic nucleus have the same number of protons For example carbon 12 most common carbon 13 rare carbon 14 rare and radioactive Radioactive isotopes Radioisotopes Most isotopes are stable Both 12C and 13C are stable isotopes Radioisotopes are unstable spontaneously give off particles and energy Carbon 14 how many protons does 14C have Isotopes can be used as a research tool Radioisotopes isotopes that emit neutrons protons and electrons Radiometric dating takes advantage of this natural phenomenon Example Over time Carbon 14 decays to Nitrogen 14 Researchers can compare Carbon 14 in atmosphere to carbon 14 in fossils remains and estimate fossil age The age of carbon containing remains less than about 50 000 years old such as this pygmy mammoth can be determined using carbon dating For older objects scientists analyze the presence of isotopes of uranium U which decays to lead potassium K or rubidium Ru Radioactive isotopes can be used in medicine diagnostic nuclear medicine behave chemically like non radioactive elements arthritis research biomedcentral com Chemical Reactivity of Elements electrons in orbital clouds of adjacent elements react some elements are more reactive than others molecules are 2 or more atoms chemically bonded together Electron Shells and the Bohr Model Bohr diagrams indicate how many electrons fill each principal shell Group 18 elements helium neon and argon are shown have a full outer or valence shell A full valence shell is the most stable electron configuration Elements in other groups have partially filled valence shells and gain or lose electrons to achieve a stable electron configuration The periodic table of the elements shows electron distribution of all elements valence shell holds 2 First shell Hydrogen 1H Atomic mass Helium 2He 2 He 4 00 Atomic number Element symbol Electron shell diagram Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine 3Li 4Be 5B 6C 7N 8O 9F Neon 10Ne 8 Second shell 8 Third shell Sodium Magnesium Aluminum Silicon Phosphorus Sulfur 16S 15P 11Na 12Mg 14Si 13Al Chlorine Argon 17Cl 18Ar The Energy Levels of Electrons electrons vary in the amount of energy they possess Energy is defined as the capacity to cause change Potential energy is the energy that matter possesses because of its location or structure The electrons of an atom Differ in the amounts of potential energy they possess Electrons are normally found at their lowest possible energy state Valence Valence electrons those in the outermost or valence shell determine the chemical behavior of an atom if valence shell is complete atom is unreactive stable an atoms reacts with other atoms to complete valence shell Octet Rule atoms need 8 electrons in valence shell for stability Every atom has a characteristic valence usually equal to the number Valence of unpaired valence electrons The valence of hydrogen is 1 Oxygen is 2 Nitrogen is 3 Memorize these Carbon is 4 Phosphorus could have a valence of 3 based on its three unpaired electrons but in biological molecules it generally has a valence of 5 Electron Orbitals An orbital is the 3D space where an electron is found 90 of the time can be filled with 2 electrons Each electron shell consists of a specific number of orbitals The shape of orbitals determines the shape of molecules which determines their biological activity Chemical Bonds The formation and function of molecules depend on chemical bonding between atoms Different types of bonds have different strengths The reactivity of atoms is due to unpaired electrons in their valence shell electrons Atoms interact by either sharing or transferring valence Chemical Bonds A molecule Consists of 2 or more atoms held together by covalent bonds A structural formula of a
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