Chapter 2 Concept 2 1 Matter Organisms are composed of matter It has three forms Solids Liquids Gases Elements and Compounds o Elements is a substance that can not be broken down further Ex Sodium o Compound Substance consisting of two or more elements in a fixed ratio Ex Sodium chloride Elements of life o 20 25 of the 92 elements are essential to life o C H O N make up about 96 of living matter o Trace Elements required by an organism in minute quantities Concept 2 2 Structure of an Atom o Neutrons No Charge o Protons Positive Charge also determines Atomic Number o Electrons Negative Charge Subatomic Particles o Proton Mass and Neutron mass are measured in Daltons 1 Dalton 1 amu o Electrons form a cloud around the nucleus When electrons and protons are equal the atom is Atomic Number and Atomic Mass neutral o Atomic number is the amount of protons o Atomic mass is neutrons protons o Isotopes are when there are more neutrons than protons Electron Distribution shells Chemical Bonds o Covalent O2 o Valence Electrons are the electrons in the outermost shell or valence o Electrons with a full valence noble gases are inert o Orbitals are where electrons can be found 90 Two elements share electrons Single Bond is a sharing of one pair of electrons Double Bond is sharing of two pairs of electrons Bonding capacity is determined by an atoms valence electrons Electronegativity is an atoms attraction for electrons in a covalent bond Oxygen and Nitrogen are very electronegative Non polar covalent bonds occur when electrons are distributed evenly Polar covalent bonds occur when one atom is more electronegative than the other which causes a partial positive d or negative d charge for each atom or molecule Form when atoms give up electrons each atom becomes o Ionic NaCl an ion Cation Positive Ion Anion Negative Ion o Weak chemical Bonds Hydrogen Bonds When a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom Van der Waals interactions Attractions between molecules that are close together as a result of these charges Important in maintaining the structure of proteins and DNA Molecular Shape and Function o Atoms shape is very important to its function o A molecule s shape is determined by the positions of its atoms valence orbitals o Biological molecules recognize and interact with each other with a specificity based on molecular shape
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