Week 5 and 6 Notes
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Date Created: 10/02/15
CHEM 111 General Chemistry Week 5 and 6 Notes gt 38 The Periodic Table and Filling Orbitals The electron con guration of an atom demonstrates how many electrons the atom has and in which block of the periodic table it falls To ll orbitals we use the Aufbau Principle the method of building electron con gurations of atoms by adding one electron at a time across the rows of the periodic table We represent this arrangement by an atom s electron con guration which we build up using the electron con guration blocks 5 Block Id Block Ilp Block If Block 5s E amFw When writing out electron con gurations you read from left to right ls 25 2p 35 3p4s3d4p The 5 block orbitals hold 2 electrons p hold 6 d hold 10 and f hold 14 so write an EC like EX Ca1squot2 25quot2 2pquot6 3squot2 3pquot6 4squot2 The total number of quotX electrons in the con guration should equal that of the atom The core electrons are the electrons in the lled inner shells in an atom or ion that are not involved in chemical reactions The valence electrons are the electrons in the outermost shell of an atom having the most in uence on the atom s chemical behavior The outmost shell is called the valence shell To ll orbitals determine the number of electrons the elements has and then write it out using a variety of methods The condensed electron con gurations use the symbol for the nearest lower noble gas in atomic number to simplify the con guration EX K Ar4squot1 rather than writing out lsquot2 25quot2 2pquot6 Remember The s block orbitals hold 2 electrons p hold 6 d hold 10 and f hold 14 Use Hund s Rule to ll orbital diagrams the lowest energy electron con guration of an atom has the maximum number of unpaired electrons all of which have the same spin in degenerate orbitals Think of it this way Guests in a hotel will occupy a different room on the same oor before sharing a room ll all diagram blocks with one electron before pairing them see pg 105 Once paired they must have opposite spins 43D I 3pm ssD 25D lls39 gt 39 Electron Con guration of Ions The same information applies for writing electron con guration for ions as it does for neutral atoms However you must determine based on the charge how many electrons the atom now has Recall that has lost an electron and has gained one so for example C 6 electrons 1squot2 2squot2 2pquot2 Cquot 5 1squot2 2squot2 2pquot1 CA 71squot2 25quot2 2pquot3 gt 310 The Sizes of Atoms and lons There are trends in the atomic radii across the periodic table Atomic radii increases from the bottom left to top right meaning that Fr is the largest and He is the smallest Cullnge 01 Saint Eencmct a n1 Junxl39i395 university geaoeeoeooo Trends also occur within ions Cations of main group elements are much smaller than their parent atom but anions are much larger in size gt 311 Ionization Energies The ionization energy IE is the amount of energy needed to remove 1 mole of electrons from 1 mole of ground state atoms or ions in the gas phase The rst lEs of the main group elements generally increase from left to right in the period and decrease from top to bottom in a group Note that this is the same pattern as the trend of atomic radii but inverse numbers atomic radii decreases from bottom left to top right while ionization increases in the same direction gt 312 Electron Affinities The electron af nity is the energy change that occurs when 1 mole of electrons combines with 1 mole of atoms or ions in the gas phase This value is expressed in kilojoules per mole The more negative the value the more energy is released when 1 mole of atoms combines with 1 mole of electrons to form 1 mole of anions with a 1 charge The values of many main group atoms are negative indicating that energy is released when they acquire electrons gt 41 Chemical Bonds lonic bonds consist of combinations of cations formed by metallic elements and anions formed from nonmetals These ions are held together by the electrostatic attraction that the ions of opposite charges have for each other The strength of this attraction is called electrostatic potential energy Lattice energy is the energy released when 1 mole of an ionic compound forms from its free ions in the gas phase A crystalline solid consists of an ordered 3D array of particles called a crystal lattice A covalent bond is a bond created by two atoms sharing one or more pairs of electrons A metallic bond is formed with metallic solids as they pool their electrons together gt 42 Naming Compounds and Writing Formulas Binary ionic compounds are usually formed by main group elements that contain a cation from group 1 2 or 13 and an anion formed by an element in groups 1517 For naming binary ionic compounds 1 The rst word is the name of the cation or parent element 2 The second name is the anion with an ending changed to ide Poyatomic ions are a charged group of more than one kind of atom joined together by covalent bonds Oxoanion is a polyatomic anion that contains at least one nonoxygen central atom bonded to one or more oxygen atoms Binary molecular compounds are two nonmetallic elements that combine to form compounds to write these names follow these three rules 1 The rst word is the name of the rst element 2 Change the ending of the second word to ide 3 Use the pre xes to indicate the number of atoms of each type of molecule but do not use mono with the rst element in the name mono 1 di 2 tri 3 tetra 4 penta 5 hexa 6 hepta 7 octa 8 nona 9 d deca 10 Binary acids elements that contain one or more ionizable hydrogen atoms are usually HX where H is hydrogen and X is a group 17 element These rules apply to binary acids 1 Add hydro to name of second element in place of hydrogen 2 Replace last syllable of element with ic followed by acid For oxoacidsoxanions that combine with H ions these rules apply 1 If the oxoanions name ends in ate replace with ic 2 If the oxanion name ends in ite the name ends in ous The pre xes ic and ous also apply to a comparison on elements ic being the smaller of the two and ous being the large in comparison gt 43 Lewis Symbols and Lewis Structures The octet rule states that atoms tend to lose gain or share electrons so that each atom has 8 valence electrons or an octet which is the principle behind Lewis structures A Lewis symbol is the chemical symbol for an element surrounded by one or more dots each representing 1 valence electron also called a Lewis dot This re ects the number of chemical bonds each atom of an element typically forms to complete the octet which is called its bonding capacity The Lewis structure is a 2D representation of the bonds and lone pairs of valence electrons in an ionic or molecular compound A bonding pair is a pair of electrons shared between two atoms A single bond is a bond that results when two atoms share one pair of electrons A lone pair is a pair of electrons that is not shared There are 5 steps to drawing Lewis structures 1 Determine the number of valence electrons 2 Arrange the symbols of the elements in a pattern that shows how their atoms are bonded Note that atoms with highest bonding capacities are toward the inside of the drawing 3 Complete the octets of all the atoms bonded to the central atom by adding lone pairs of electrons 4 Compare the number of valence electrons in the Lewis structure to the number determined in step 1 5 Complete the octet on the central atom Molecules may form double bonds two atoms sharing two pairs of electrons and triple bonds a bond that results when two atoms share three pairs of electrons
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