review of atomic structure chemical bonding types of chemical bonds what is a chemical bond?

Transcription

1 review of atomic structure atom - basic, indivisible unit of matter that still retains the chemical identity of an element valence shell - the outermost electron shell for an atom valence electron - electron found in the valence shell; involved in forming chemical bonds nucleus - core of an atom; contains protons and neutrons chemical bonding nucleus valence shell magnesium atom (Mg) valence electron what is a chemical bond? types of chemical bonds formed when atoms lose, gain, or share valence electrons in order to become isoelectronic to one of the noble gases bond type definition when is the bond formed isoelectronic - two particles with identical electron configurations formed to achieve a full valence shell (8 electrons) 2 e ionic bond electronic attraction between a cation (positive) and an anion (negative) between a metal cation (positive) and a nonmetal anion (negative); polyatomic cations and anions p lose 2 electrons 12 p 10 p 10 Ne 18 Ar 36 Kr covalent bond metallic bond sharing of electrons between 2 elements communal sharing of electrons between metallic atoms between 2 nonmetallic atoms; metalloids metallic atoms magnesium atom (Mg) magnesium ion (Mg 2+ ) neon atom (Ne) isoelectronic particles 54 Xe 86 Rn coordinate bond donation of a pair of electrons from one particle to another transition metals and covalent molecules or nonmetals

2 chemical bonds - ionic bond the electronic attraction between a positive cation and a negative anion formed between a metal cation and a nonmetal anion polyatomic ions (charged molecules) form ionic bonds ionic compounds are overall neutral; no net charge lose 1 e - (transfers to Cl) 3 p 3 p 9 p 9 p writing neutral formulas for ionic compounds Li 1+ Cl 1- cation charge = anion subscript Li1Cl1 subscripts of 1 are implied LiCl anion charge = cation subscript writing neutral formulas for ionic compounds writing neutral formulas for ionic compounds Ba 2+ Cl 1- cation charge = anion subscript Ba1Cl2 subscripts of 1 are implied anion charge = cation subscript Ba 2+ O 2- cation charge = anion subscript Ba2O2 reduce to simplest form anion charge = cation subscript BaCl2 BaO

3 writing neutral formulas for ionic compounds Ba 2+ PO4 3- cation charge = anion subscript use parenthesis when there is more than one polyatomic ion Ba3(PO4)2 anion charge = cation subscript polyatomic ions covalently bonded molecules that carry either a positive or negative charge formula name BrO3 - bromate acetate ClO3 - chlorate CN - cyanide SCN - thiocyanate CO3 2- carbonate CrO4 2- chromate IO3 - iodate MnO4 - permanganate N4 + ammonium NO3 - nitrate O - hydroxide PO4 3- phosphate S2O3 2- thiosulfate SiO3 2- silicate SO4 2- sulfate C23O2 - Na + + PO4 3- neutral formula Na3PO4 Al 3+ + SO4 2- neutral formula Al2(PO4)3 Ba 2+ + CrO4 2- neutral formula BaCrO4 ( ) to indicate multiple polyatomic ions Al2(PO4)3 versus correct Al2PO43 incorrect naming binary ionic compounds naming compounds with transition metals compound name is broken into two portions: cation (metal) portion - written first; same as the name of the element anion (nonmetal) portion - written second; drop ending, replace with -ide polyatomic ion - name does not change certain transition metals can be multivalent can form several differently charged ions depending on the circumstances roman numerals used to differentiate between charges known as the stock naming system element element symbol ion ion symbol fluorine F fluoride F - chlorine Cl chloride Cl - bromine Br bromide Br - iodine I iodide I - nitrogen N nitride N 3- phosphor P phosphi P 3- NaCl - sodium chloride K2O - potassium bromide Al3(PO4)2 - aluminum phosphate N4O - ammonium hydroxide ion symbol Fe 2+ Fe 3+ Fe 4+ Cr 2+ Cr 3+ Pb 2+ ion name iron (II) iron (III) iron (IV) chromium (II) chromium lead (II) chemical symbol PbSO4 Sn3(PO4)2 FeCl2 FeCl3 CrF2 CrF3 chemical name lead (II) sulfate tin (II) phosphate FeCl2 - iron (II) chloride FeCl3 - iron (III) chloride CrF2 - chromium (II) CrF3 - chromium (III) oxygen O oxide O 2- sulfur S sulfide S 2- (N4)2O - ammonium oxide Pb 4+ Sn 2+ lead (IV) tin (II) Cr(O)2 Cr(O)3 chromium (II) hydroxide chromium (III) hydroxide selenium Se selenide Se 2- Sn 4+ tin (IV) Fe(O)3 iron (III) hydroxide

4 properties of ionic compounds chemical bonds - covalent bond high melting and boiling points the sharing of a pair of electrons between two atoms solid at room temperature highly organized (crystalline) structure brittle soluble in water Na + Cl - formed between nonmetal (or metalloid) atoms since electrons are shared, there are no ions formed and no overall charge sharing of electrons occurs when the valance shells of the two atoms overlap conductors of electricity in molten or dissolved state - ions can move freely insulators in the solid state - ions locked in place + overlap of valance shells 1 p 1 p 1 p 1 p hydrogen atom (1valance e - ) hydrogen atom (1valance e - ) hydrogen molecule (2 valance e - ) covalent bonds - diatomic elements diatomic refers to a 2 atom covalent molecule certain elements do not exist as individual atoms, but as diatomic molecules exist when elements are too reactive to exist as individual atoms naming covalent compounds name of the 1 st element does not change ending of 2 nd element is dropped and replaced with -ide prefixes before each element denote how many of each atom are in the molecule prefix mono- omitted for the first element element name hydrogen nitrogen oxygen chlorine fluorine bromine iodine element symbol 2 N2 O2 Cl2 F2 Br2 I2 1 p hydrogen molecule (1valance e - ) 9 p 1 p 9 p fluorine molecule (8 valance e - ) prefix number mono- 1 di- 2 tri 3 tetra- 4 penta- 5 hexa- 6 hepta- 7 octa- 8 nona- 9 deca- 10 chemical symbol CO2 CO N2O4 PCl3 PCl5 SF6 P2O5 P4O10 S2O3 chemical name carbon dioxide carbon monoxide dinitrogen tetroxide phosphorus trichloride phosphorus sulfur hexafluoride diphosphorus pentoxide tetraphosphorus disulfur trioxide

5 properties of covalent compounds valance shell electron pair repulsion theory lower melting and boiling points many are liquids/gases at room temperature low degree of organization (not crystalline) many will dissolve in water, many will not insulate against the flow of electricity - no ions formed many plastics are covalent compounds (hydrocarbons) abbreviated as VSEPR theory atoms in a molecule will maximize their distance from other atoms in the molecule in order to minimize electron-electron repulsions larger bond angles correspond to lower energy molecular structures that are generally more stable than those with smaller dihedral bond angles central atom is considered the angle s vertex e - e - measured from one surrounding atom, through the central atom, to another surrounding atom o o polyethylene plastic 107 o o o σ π sigma ( ) and pi ( ) covalent bonds AXE method for naming molecular geometries A - central atom in the covalent molecule to which all other atoms are bonded sigma bond exists in-line with atomic nuclei involved in the bond X - all atoms connected to the central atom E - unshared electron pairs present on the central atom stronger type of covalent bond pi bond π exists above and below atomic nuclei involved in the bond weaker type of covalent bond sigma σ pi N.. ammonia, N3 - AB3E 1 - central atom (N) 3 - bonded atoms () 1 - unshared e - pair on N methane, C4 - AB4 1 - central atom (C) 3 - bonded atoms () C

6 linear molecular geometry tetrahedral molecular geometry molecules of the general structure: molecules of the general structure: AB4 (example: C4, CCl4 ) A - A (example: N2, 2) A - B (example: Cl, F) methane chloroform B = A = B (example: CO2, SiO2) molecules exhibit a 180 o bond angle; straight line symmetry found in A - A and B = A = B type molecules molecules exhibit four equivalent o bond angles symmetry found in AB4 type molecules where all B are identical trigonal pyramid molecular geometry molecules of the general structure: AB3E (example: N3, P3) trigonal planar molecular geometry molecules of the general structure: AB3 (example: BF3, B3) ammonia phosphine formaldehyde boron trifluoride molecules exhibit a 107 o bond angle lack of symmetry due to increased e - pair repulsions and decreased bond angle unshared e - pairs push atoms closer together, decreasing the bond angle molecules exhibit a 120 o bond angle symmetry found in AB3 type molecules where all B are identical atoms

7 bent molecular geometry trigonal bipyramidal molecular geometry molecules of the general structure: AB5 (examples: PCl5, AsBr5) molecules of the general structure: AB2E2 (example: 2O, SCl2) sulfur dichloride water arsenic pentafluoride phosphorus pentachloride molecules exhibit a 105 o bond angle lack of symmetry due to e - pair repulsions and decreased bond angle molecules exhibit a 90 o, 180 o, and 120 o bond angles symmetry found in AB5 type molecules where all B are identical see - saw molecular geometry T - shaped molecular geometry molecules of the general structure: AB4E (SF4, TeI4) molecules of the general structure: AB3E2 (example: ClF3) selenium tetrafluoride sulfur tetrafluoride chlorine trifluoride molecules exhibit a 90 o, 180 o, and 120 o bond angles lack of symmetry due to unshared e - pair molecules exhibit a 90 o and 180 o bond angles lack of symmetry due to unshared e - pair

8 linear molecular geometry molecules of the general structure: AB2E3 (example: XeF2) octahedral molecular geometry molecules of the general structure: AB6 (example: SF6) sulfur hexafluoride xenon difluoride molecules exhibit a 180 o bond angles symmetry due to linear nature of molecule molecules exhibit a 90 o and 180 o bond angles symmetry found in AB6 type molecules where all B are identical square pyramid molecular geometry square planar molecular geometry molecules of the general structure: AB5E (BrF5, ClF5) molecules of the general structure: AB4E2 (example: XeF4) bromine pentafluoride xenon tetrafluoride chlorine pentafluoride molecules exhibit a 90 o and 180 o bond angles lack of symmetry due to unshared e - pair molecules exhibit a 90 o and 180 o bond angles symmetry due to unshared e- pairs above and below the molecule

9 other noteworthy molecular geometries pentagonal bipyramidal, IF7 chemical equivalency - axial and equatorial atoms axial - atoms pointing straight up and down in 3D space equatorial - atoms forming the central plane of a molecule axial atoms pentagonal pyramidal, XeOF5 - planar pentagonal, XeF5 - square antiprismatic, XeF8 2- equatorial atoms tricapped trigonal prismatic, Re9 2- surrounding atoms in octahedral molecules are chemically equivalent equatorial atoms are lower energy in trigonal bipyramidal molecules ligands - molecules with coordinate bonds bond and molecule polarity covalent bond - chemical bond where each atom in the bond shares a single electron, forming a two electron bond coordinate bond - a non-covalent bond in which one atom or molecule donates both electrons for the attraction bond polarity refers to how evenly electrons are shared in a chemical bond molecular polarity refers to how evenly electrons are distributed throughout a molecule bond polarity is determined using differences in electronegativity (END) molecule is overall non-polar if all dipoles (polar bonds) cancel out this happens when a covalent molecule has: a symmetrical 3D molecular geometry all atoms bonded to the central atom are identical molybdenum hexacarbonyl, Mo(CO)6 hexamethyl tungsten, W(C3)6

10 chemical bond polarity dipole arrows to show bond polarity measure of how evenly electrons are shared in a chemical bond calculated using electronegativity differences (END) point from the atom of lower EN to the atom of higher EN dipole arrows show the direction of electron flow in a polar bond END bond type non-polar covalent bond moderately polar covalent bond very polar covalent bond > 2.0 ionic bond based on Linus Pauling s electronegativity scale ( ) linus pauling each dipole (polar bond) is identical, and the molecule has symmetry; the dipoles cancel each other out overall, CO2 is a non-polar molecule polar versus non-polar molecules dipole arrows: methane vs. chloroform dipole arrows point from atom of lower EN to atom of higher EN point from atom of lower EN to atom of higher EN CO2 COS each dipole (polar bond) is identical the molecule has symmetry overall, CO2 is a non-polar molecule dipoles are asymmetrical the molecule lacks symmetry overall, COS is a polar molecule non-polar polar

11 dipoles line up in an electric field molecular hybridization atomic orbital (AO) - describes behavior of e- pairs in an atom molecular orbital (MO) - describes behavior of e- pairs in a molecule orbital hybridization - s, p, d, and f atomic orbitals hybridize or mix as covalent bonds are formed the resulting hybrid orbitals appear as a combination of s, p, d, and f orbitals the more EN end of one molecule will line up with the less EN end of another molecule