Unit One Chemistry and Cells I Matter consists of chemical elements in pure form and in combinations called compounds A Matter defined as anything that takes up space and has mass B Elements and Compounds 1 Element substance that cannot be broken down to other substances by chemical reactions 92 recognized 2 Compound substance consisting of two or more different elements combined in a fixed ratio element occurring in nature element compound C The Elements of Life 1 Essential elements any chemical element required by an organism for healthy growth or survival and reproduction Similar among organisms but there are variations Humans need 25 elements but plants need only 17 Oxygen O Carbon C Hydrogen H and Nitrogen N 96 of living matter 2 Trace Elements required by an organism in only minute quantities Iron FE trace element needed by all forms of life Other trace elements may only be needed depending on the species D Evolution of Tolerance to Toxic Elements 1 Some naturally occurring elements are toxic to organisms EX Sunflower plants can take up lead zinc and other heavy metals in concentrations that would kill most organisms Possibly variants of ancestral sunflower species arose in heavy metal laden soils and subsequent natural selection resulted in their survival and reproduction 2 Subatomic Particles atom is smallest unit having properties of an element atoms composed of even smaller parts called subatomic particles subatomic particles would be particles like neutrons protons and electrons there are more than 100 identified subatomic particles proton and electron are electrically charged protons electron neutron neutral protons and neutrons packed together in dense core atomic nucleus at the center of the atom protons give neutrons charge Electrons from cloud of charge around nucleus attraction btwn opposite charges keep electrons in vicinity of nucleus neutron and proton in mass 1 7x10 4 grams g Dalton measurement used for atoms subatomic particles and molecules all atoms of particular element have same of protons in nuclei electron is 1 2000 that of a proton or neutron APE atomic the amount of protons or the amount of electrons same amount 3 Atomic and Atomic Mass Atomic Number is of protons written as subscript to left element unless otherwise specified atom is neutral in electrical of protons of electrons Mass Number protons Neutrons in the atom nucleus written as superscript to left of an element Atomic Mass Atomic Number Amount of Neutrons 4 Isotopes Istopes Atoms of the same element that have the same amount of protons but different numbers of neutrons in nature an element occurs as a mixture of its isotopes isotopes of an element have slightly different masses they behave identically in chemical reactions Stable Isotopes nuclei that doesn t have tendency to lose particles Radioactive Isotopes nucleus decays spontaneously giving off particles and energy decay changing of protons transforms the atom to an atom of a different element EX 14 C decays it becomes an atom of Nitrogen radioactive isotopes can be used to follow atoms through metabolism radioactive tracers important diagnostic tools used in imaging instruments PET scanners for example radiation from decaying isotopes can also damage cellular molecules 5 The Energy Levels of Electrons only electrons are directly involved in the chemical reactions btwn atoms Energy capacity to cause change by doing work atoms electrons vary in amount of energy they possess Potential Energy energy that matter possesses because of its location or structure water at in reservoir has potential energy bc of its altitude Matter has natural tendency to move to lowest state of potential energy Electrons have potential energy bc of how they are arranged in relation to the nucleus Electrons attracted to nucleus it takes work for electron to get farther from nucleus the farther away it is the greater potential energy it has changes in potential energy in electrons can only occur in fixed amounts electron cannot exist btwn energy levels energy level correlated with distance to nucleus Electron shells orbit followed by electrons around an atoms nucleus 1st shell closest to nucleus lowest energy level change shell by losing absorbing amount of energy to difference in potential energy btwn its position in the old shell and new shell 6 Electron Distribution and Chemical Properties electron 1st shell can only hold 2 electrons at max electron 2nd shell can only hold 8 electrons at max Valence Electrons outer electrons in outermost electron shell Valence Shell Chemical behavior of atom depends on electrons in Valence shell atoms w same of Valence Electrons exhibit similar chemical behavior atom w completed valence shell is unreactive Inert chemically unreactive Helium Neon Argon only 3 elements w full valence shell reactivity of atom arises from presence of 1 or more unpaired electrons in its valence shell atoms interact in a way that completes their valence shells II The Formation and Function of Molecules Depend on Chemical Bonding between Atoms 1 Chemical Bonds attractions between atoms that keep them close together when sharing transferring valence electrons Covalent and Ionic bonds are the strongest chemical bonds 2 Covalent sharing pair of valence electrons by two atoms can only Hydrogen 1 valence electron bonding w another Hydrogen now have two electrons between them filling their valence shell now a hydrogen molecule 2 0r more atoms held by covalent bonds molecule electron distribution can be depicted by a structural formula Ex H H line represents a single bond pair of shared electrons Space filling model represents actual shape of molecule Double bond atoms sharing 2 pairs of valence electrons Ex Oxygen has 6 electrons in 2nd shell needs 2 more to complete shell 2 Oxygen s form by sharing 2 valence electrons This results in a double bond O O Bonding capacity is called the atoms Valence usually equals of electrons required to complete the atoms Valence shell Compound combination of two or more different elements Electronegativity attraction of a particular atom for the electrons of a covalent bond the more electronegative an atom is the more strongly it pulls the shared electrons toward itself atoms of same element electrons shared equally bc they have the same electronegativity Nonpolar Covalent Bond atoms share electrons together equally Polar Covalent Bond atoms share electrons unequally 3 Ionic Bonds attraction between two oppositely